CEREBRUM
The cerebrum or telencephalon, together with the diencephalon, constitute the forebrain. It is the most anterior or, especially in humans, most superior region of the vertebrate central nervous system. "Telencephalon" refers to the embryonic structure, from which the mature "cerebrum" develops. The dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into symmetric left and right cerebral hemispheres.
Development
During vertebrate embryonic development, the prosencephalon, the most anterior of three vesicles that form from the embryonic neural tube, is further subdivided into the telencephalon and diencephalon. The telencephalon then forms two lateral telencephalic vesicles which develop into the left and right cerebral hemispheres.
Hemispheres
left side controls right side of body
right side controls left side of body
Structure
The cerebrum is composed of the following sub-regions:
Cerebral cortex, or cortices of the cerebral hemispheres
Basal ganglia, or basal nuclei
Limbic System
Composition
The cerebrum comprises what most people think of as the "brain." It lies in front or on top of the brainstem and in humans is the largest and most well-developed of the five major divisions of the brain. The cerebrum is the newest structure in the phylogenetic sense, with mammals having the largest and most well-developed among all species. In larger mammals, the cerebral cortex is folded into many gyri and sulci, which has allowed the cortex to expand in surface area without taking up much greater volume.
In humans, the cerebrum surrounds older parts of the brain. Limbic, olfactory, and motor systems project fibers from the cerebrum to the brainstem and spinal cord. Cognitive and volitive systems project fibers from the cerebrum to the thalamus and to specific regions of the midbrain. The neural networks of the cerebrum facilitate complex behaviors such as social interactions, learning, working memory, and in humans, speech and language.
Functions
Note: As the cerebrum is a gross division with many subdivisions and sub-regions, it is important to state that this section lists the functions that the cerebrum as a whole serves. See main articles on cerebral cortex and basal ganglia for more information.
Movement
The cerebrum directs the conscious or volitional motor functions of the body. These functions originate within the primary motor cortex and other frontal lobe motor areas where actions are planned. Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons, which innervate the muscles. Damage to motor areas of cortex can lead to certain types of motor neuron disease. This kind of damage results in loss of muscular power and precision rather than total paralysis.
Sensory processing
The primary sensory areas of the cerebral cortex receive and process visual, auditory, somatosensory, gustatory, and olfactory information. Together with association cortical areas, these brain regions synthesize sensory information into our perceptions of the world around us.
Olfaction
Main article: Olfaction
The olfactory bulb in most vertebrates is the most anterior portion of the cerebrum, and makes up a relatively large proportion of the telencephalon. However, in humans, this part of the brain is much smaller, and lies underneath the frontal lobe. The olfactory sensory system is unique in the sense that neurons in the olfactory bulb send their axons directly to the olfactory cortex, rather than to the thalamus first. Damage to the olfactory bulb results in a loss of the sense of smell.
Language and communication
Main article: Language
Speech and language are mainly attributed to parts of the cerebral cortex. Motor portions of language are attributed to Broca's area within the frontal lobe. Speech comprehension is attributed to Wernicke's area, at the temporal-parietal lobe junction. These two regions are interconnected by a large white matter tract, the arcuate fasciculus. Damage to the Broca's area results in expressive aphasia (non-fluent aphasia) while damage to Wernicke's area results in receptive aphasia (also called fluent aphasia).
Learning and memory
Main article: Memory
Explicit or declarative (factual) memory formation is attributed to the hippocampus and associated regions of the medial temporal lobe. This association was originally described after a patient known as HM had both his hippocampuses (left and right) surgically removed to treat severe epilepsy. After surgery, HM had anterograde amnesia, or the inability to form new memories.
Implicit or procedural memory, such as complex motor behaviors, involve the basal ganglia.
Cell regeneration in Xenopus laevis
[edit] Larval stage
In a study of the telencephalon conducted in Hokkaido University on African clawed frogs (xenopus laevis)[1], it was discovered that, during larval stages, the telencephalon was able to regenerate around half of the anterior portion (otherwise known as partially truncated), after a reconstruction of a would-be accident, or malformation of features.
The regeneration and active proliferation of cells within the clawed frog is quite remarkable, regenerated cells being almost functionally identical to the ones originally found in the brain after birth, despite the lack of brain matter for a sustained period of time.
This kind of regeneration depends on ependymal layer cells covering the cerebral lateral ventricles, within a short period before, or within the initial stage of wound-healing. This is observed within the stages of healing within larvae of the clawed frog.
[edit] Developed stage
The regeneration within the developed stage of the clawed frog is different from that in the larval stage. Because the cells adhere to one another, they are unable to form an entity that can cover the cerebral lateral ventricles. Thus, the telencephalon remains truncated and the loss of function becomes permanent.
[edit] Effects of abnormality
After removing over half of the telencephalon in the developed stage of the clawed frog, the lack of functions within the animal was apparent, manifesting with obvious difficulties in movement, nonverbal communication between other species, as well as other difficulties thought to be similar to those seen in humans.
This kind of regeneration is still relatively unknown in regard to regeneration within larval stages, similar to the human fetal stage.
[edit] Variation among species
In the most primitive living vertebrates, the hagfishes and lampreys, the cerebrum is a relatively simple structure receiving nerve impulses from the olfactory bulb. In cartilaginous and lobe-finned fishes, and also in amphibians, a more complex structure is present, with the cerebrum being divided into three distinct regions. The lowermost (or ventral) region forms the basal nuclei, and contains fibres connecting the rest of the cerebrum to the thalamus. Above this, and forming the lateral part of the cerebrum, is the paleopallium, while the uppermost (or dorsal) part is referred to as the archipallium. The cerebrum remains largely devoted to olfactory sensation in these animals, despite its much wider range of functions in amniotes.[2]
In ray-finned fishes, the structure is somewhat different. The inner surfaces of the lateral and ventral regions of the cerebrum bulge up into the ventricles; these include both the basal nuclei and the various parts of the pallium, and may be complex in structure, especially in teleosts. The dorsal surface of the cerebrum is membranous, and does not contain any nervous tissue.[3]
In the amniotes, the cerebrum becomes increasingly large and complex. In reptiles, the paleopallium is much larger than in amphibians, and its growth has pushed the basal nuclei into the central regions of the cerebrum. As in the lower vertebrates, the grey matter is generally located beneath the white matter, but in some reptiles, it spreads out to the surface to form a primitive cortex, especially in the anterior part of the brain.[4]
In mammals, this development proceeds further, so that the cortex covers almost the whole of the cerebral hemispheres, especially in more "advanced" species, such as primates. The paleopallium is pushed to the ventral surface of the brain, where it becomes the olfactory lobes, while the archipallium becomes rolled over at the medial dorsal edge to form the hippocampus. In placental mammals, a corpus callosum also develops, further connecting the two hemispheres. The complex convolutions of the cerebral surface are also found only in higher mammals.[5]
The cerebrum of birds has evolved along different lines to that of mammals, although they are similarly enlarged, by comparison with reptiles. However, this enlargement is largely due to the basal ganglia, with the other areas remaining relatively primitive in structure. For example, there is no great expansion of the cerebral cortex, as there is in mammals. Instead, an HVC develops just above the basal ganglia, and this appears to be the area of the bird brain most concerned with learning complex tasks.[6]
Tuesday, February 2, 2010
Respiratory System
Respiratory System
The respiratory system's function is to allow gas exchange to all parts of the body. The space between the alveoli and the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism. In humans and other mammals, for example, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.[1]
Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.
Anatomy in vertebrates
[edit] Mammals
For mammals, including humans, respiration is essential. In these organisms, the respiratory system can be subdivided into an upper respiratory tract and a lower respiratory tract based on anatomical features. The upper respiratory tract includes the nasal passages, pharynx and the larynx, while the lower respiratory tract comprises the trachea, the primary bronchi and lungs. The respiratory system can also be divided into physiological, or functional, zones. These include the conducting zone (the region for gas transport from the outside atmosphere to just above the alveoli), the transitional zone, and the respiratory zone (the alveolar region where gas exchange occurs).[2] (See also respiratory tract.)
[edit] Comparative anatomy and physiology
[edit] Horses
Horses are obligate nasal breathers. That is, they are different from many other mammals in that they do not have the option of breathing through their mouths and must take in air through their nose.[3] (See also Respiratory system of the horse.)
[edit] Elephants
The elephant is the only animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue.[4] This lack of a pleural space, along with an unusually thick diaphragm, are thought to be evolutionary adaptations allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.[5]
[edit] Birds
The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as air sacs. The lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli. See Avian respiratory system for a detailed description of these and other. features.
[edit] Reptiles
The anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli, however. Reptiles do not possess a diaphragm. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration.[6]
See also reptiles for more detailed descriptions of the respiratory system in these animals.
[edit] Amphibians
Both the lungs and the skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.[7]
[edit] Fish
In most fish the respiration takes place through gills. (See also aquatic respiration.) Lungfish, however, do possess one or two lungs. The labyrinth fish have developed a special organ that allows them to take advantage of the oxygen of the air, but is not a true lung.
[edit] Anatomy in invertebrates
[edit] Insects
Air enters the respiratory system of most insects through a series of external openings called spiracles. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely-networked array of tubes called trachea. The tracheal system within an individual is composed of interconnecting transverse and longitudinal tracheae which maintain equivalent pressure throughout the system. These tracheae branch repeatedly, eventually forming tracheoles, which are blind-ended, water-filled compartments only one micrometer in diameter.[8] It is at this level of the tracheoles that oxygen is delivered to the cells for respiration.
Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Others, however, utilize muscular contraction of the abdomen along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns. The most extreme form of these patterns is termed discontinuous gas exchange cycles (DGC).[9]
[edit] Mollusks
Mollusks generally possess gills that allow exchange of oxygen from an aqueous environment into the circulatory system. These animals also possess a heart that pumps blood which contains hemocyanin as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The respiratory system of gastropods can include either gills or a lung.
[edit] Physiology in mammals
For more detailed descriptions see also Respiratory physiology or Respiration.
[edit] Ventilation
Ventilation of the lungs is carried out by the muscles of respiration.
[edit] Control
Ventilation occurs under the control of the autonomic nervous system from parts of the brain stem, the medulla oblongata and the pons. This area of the brain forms the respiration regulatory center, a series of interconnected brain cells within the lower and middle brain stem which coordinate respiratory movements. The sections are the pneumotaxic center, the apneustic center, and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped and/or shaken violently. The result can be death due to "shaken baby syndrome."[10]
[edit] Inhalation
Inhalation is initiated by the diaphragm and supported by the external intercostal muscles. Normal resting respirations are 10 to 18 breaths per minute, with a time period of 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, accessory muscles of respiration are recruited for support. These consist of sternocleidomastoid, platysma, and the scalene muscles of the neck.
Under normal conditions, the diaphragm is the primary driver of inhalation. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume and negative (suction) pressure (with respect to atmospheric pressure) inside the thorax. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
During forced inhalation, as when taking a deep breath, the external intercostal muscles and accessory muscles aid in further expanding the thoracic cavity.
[edit] Exhalation
Exhalation is generally a passive process; however, active or forced exhalation is achieved by the abdominal and the internal intercostal muscles. During this process air is forced or exhaled out.
The lungs have a natural elasticity: as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.[11]
During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.
[edit] Gas exchange
The major function of the respiratory system is gas exchange between the external environment and an organism's circulatory system. In humans and mammals, this exchange facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis. If proper ventilation is not maintained, two opposing conditions could occur: respiratory acidosis, a life threatening condition, and respiratory alkalosis.
Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres). These walls are composed of a single layer of epithelial cells (type I and type II epithelial cells) in close proximity to the pulmonary capillaries which are composed of a single layer of endothelial cells. The close proximity of these two cell types allows permeability to gases and, hence, gas exchange. This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference. When the atmospheric pressure is low outside the air from lungs flow out. When the air pressure is low inside, then the vice versa.
[edit] Non-respiratory functions
[edit] Vocalization
The movement of gas through the larynx, pharynx and mouth allows humans to speak, or phonate. Vocalization, or singing, in birds occurs via the syrinx, an organ located at the base of the trachea. The vibration of air flowing across the larynx (vocal chords), in humans, and the syrinx, in birds, results in sound. Because of this, gas movement is extremely vital for communication purposes.
[edit] Temperature control
Panting in dogs and some other animals provides a means of controlling body temperature. This physiological response is used as a cooling mechanism.
[edit] Coughing and sneezing
Irritation of nerves within the nasal passages or airways, can induce coughing and sneezing. These responses cause air to be expelled forcefully from the trachea or nose, respectively. In this manner, irritants caught in the mucus which lines the respiratory tract are expelled or moved to the mouth where they can be swallowed.
[edit] Development in animals
[edit] Humans and mammals
Further information: Development of human lung
The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system becomes fully functional upon exposure to air, although some lung development and growth continues throughout childhood. Pre-term birth can lead to infants with under-developed lungs. These lungs show incomplete development of the alveolar type II cells, cells that produce surfactant. The lungs of pre-term infants may not function well because the lack of surfactant leads to increased surface tension within the alveoli. Thus, many alveoli collapse such that no gas exchange can occur within some or most regions of an infant's lungs, a condition termed respiratory distress syndrome. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using steroids as a means of furthering development of type II alveolar cells.[12] In fact, once a pre-mature birth is threatened, every effort is made to delay the birth, and a series of steroid shots is frequently administered to the mother during this delay in an effort to promote lung growth.[13]
[edit] Disease
Disorders of the respiratory system can be classified into four general areas:
Obstructive conditions (e.g., emphysema, bronchitis, asthma attacks)
Restrictive conditions (e.g., fibrosis, sarcoidosis, alveolar damage, pleural effusion)
Vascular diseases (e.g., pulmonary edema, pulmonary embolism, pulmonary hypertension)
Infectious, environmental and other "diseases" (e.g., pneumonia, tuberculosis, asbestosis, particulate pollutants): Coughing is of major importance, as it is the body's main method to remove dust, mucus, saliva, and other debris from the lungs. Inability to cough can lead to infection. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.
The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent pathogens from entering the body.
Disorders of the respiratory system are usually treated internally by a pulmonologist.
[edit] Plants
Plants use carbon dioxide gas in the process of photosynthesis, and then exhale oxygen gas, a waste product of photosynthesis. However, plants also sometimes respire as humans do, taking in oxygen and producing carbon dioxide.
Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes on the undersides of their leaves known as stomata (sing:stoma). However, most plants require little air.[citation needed] Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
The respiratory system's function is to allow gas exchange to all parts of the body. The space between the alveoli and the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism. In humans and other mammals, for example, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.[1]
Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.
Anatomy in vertebrates
[edit] Mammals
For mammals, including humans, respiration is essential. In these organisms, the respiratory system can be subdivided into an upper respiratory tract and a lower respiratory tract based on anatomical features. The upper respiratory tract includes the nasal passages, pharynx and the larynx, while the lower respiratory tract comprises the trachea, the primary bronchi and lungs. The respiratory system can also be divided into physiological, or functional, zones. These include the conducting zone (the region for gas transport from the outside atmosphere to just above the alveoli), the transitional zone, and the respiratory zone (the alveolar region where gas exchange occurs).[2] (See also respiratory tract.)
[edit] Comparative anatomy and physiology
[edit] Horses
Horses are obligate nasal breathers. That is, they are different from many other mammals in that they do not have the option of breathing through their mouths and must take in air through their nose.[3] (See also Respiratory system of the horse.)
[edit] Elephants
The elephant is the only animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue.[4] This lack of a pleural space, along with an unusually thick diaphragm, are thought to be evolutionary adaptations allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.[5]
[edit] Birds
The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as air sacs. The lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli. See Avian respiratory system for a detailed description of these and other. features.
[edit] Reptiles
The anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli, however. Reptiles do not possess a diaphragm. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration.[6]
See also reptiles for more detailed descriptions of the respiratory system in these animals.
[edit] Amphibians
Both the lungs and the skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.[7]
[edit] Fish
In most fish the respiration takes place through gills. (See also aquatic respiration.) Lungfish, however, do possess one or two lungs. The labyrinth fish have developed a special organ that allows them to take advantage of the oxygen of the air, but is not a true lung.
[edit] Anatomy in invertebrates
[edit] Insects
Air enters the respiratory system of most insects through a series of external openings called spiracles. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely-networked array of tubes called trachea. The tracheal system within an individual is composed of interconnecting transverse and longitudinal tracheae which maintain equivalent pressure throughout the system. These tracheae branch repeatedly, eventually forming tracheoles, which are blind-ended, water-filled compartments only one micrometer in diameter.[8] It is at this level of the tracheoles that oxygen is delivered to the cells for respiration.
Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Others, however, utilize muscular contraction of the abdomen along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns. The most extreme form of these patterns is termed discontinuous gas exchange cycles (DGC).[9]
[edit] Mollusks
Mollusks generally possess gills that allow exchange of oxygen from an aqueous environment into the circulatory system. These animals also possess a heart that pumps blood which contains hemocyanin as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The respiratory system of gastropods can include either gills or a lung.
[edit] Physiology in mammals
For more detailed descriptions see also Respiratory physiology or Respiration.
[edit] Ventilation
Ventilation of the lungs is carried out by the muscles of respiration.
[edit] Control
Ventilation occurs under the control of the autonomic nervous system from parts of the brain stem, the medulla oblongata and the pons. This area of the brain forms the respiration regulatory center, a series of interconnected brain cells within the lower and middle brain stem which coordinate respiratory movements. The sections are the pneumotaxic center, the apneustic center, and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped and/or shaken violently. The result can be death due to "shaken baby syndrome."[10]
[edit] Inhalation
Inhalation is initiated by the diaphragm and supported by the external intercostal muscles. Normal resting respirations are 10 to 18 breaths per minute, with a time period of 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, accessory muscles of respiration are recruited for support. These consist of sternocleidomastoid, platysma, and the scalene muscles of the neck.
Under normal conditions, the diaphragm is the primary driver of inhalation. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume and negative (suction) pressure (with respect to atmospheric pressure) inside the thorax. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
During forced inhalation, as when taking a deep breath, the external intercostal muscles and accessory muscles aid in further expanding the thoracic cavity.
[edit] Exhalation
Exhalation is generally a passive process; however, active or forced exhalation is achieved by the abdominal and the internal intercostal muscles. During this process air is forced or exhaled out.
The lungs have a natural elasticity: as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.[11]
During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.
[edit] Gas exchange
The major function of the respiratory system is gas exchange between the external environment and an organism's circulatory system. In humans and mammals, this exchange facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis. If proper ventilation is not maintained, two opposing conditions could occur: respiratory acidosis, a life threatening condition, and respiratory alkalosis.
Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres). These walls are composed of a single layer of epithelial cells (type I and type II epithelial cells) in close proximity to the pulmonary capillaries which are composed of a single layer of endothelial cells. The close proximity of these two cell types allows permeability to gases and, hence, gas exchange. This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference. When the atmospheric pressure is low outside the air from lungs flow out. When the air pressure is low inside, then the vice versa.
[edit] Non-respiratory functions
[edit] Vocalization
The movement of gas through the larynx, pharynx and mouth allows humans to speak, or phonate. Vocalization, or singing, in birds occurs via the syrinx, an organ located at the base of the trachea. The vibration of air flowing across the larynx (vocal chords), in humans, and the syrinx, in birds, results in sound. Because of this, gas movement is extremely vital for communication purposes.
[edit] Temperature control
Panting in dogs and some other animals provides a means of controlling body temperature. This physiological response is used as a cooling mechanism.
[edit] Coughing and sneezing
Irritation of nerves within the nasal passages or airways, can induce coughing and sneezing. These responses cause air to be expelled forcefully from the trachea or nose, respectively. In this manner, irritants caught in the mucus which lines the respiratory tract are expelled or moved to the mouth where they can be swallowed.
[edit] Development in animals
[edit] Humans and mammals
Further information: Development of human lung
The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system becomes fully functional upon exposure to air, although some lung development and growth continues throughout childhood. Pre-term birth can lead to infants with under-developed lungs. These lungs show incomplete development of the alveolar type II cells, cells that produce surfactant. The lungs of pre-term infants may not function well because the lack of surfactant leads to increased surface tension within the alveoli. Thus, many alveoli collapse such that no gas exchange can occur within some or most regions of an infant's lungs, a condition termed respiratory distress syndrome. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using steroids as a means of furthering development of type II alveolar cells.[12] In fact, once a pre-mature birth is threatened, every effort is made to delay the birth, and a series of steroid shots is frequently administered to the mother during this delay in an effort to promote lung growth.[13]
[edit] Disease
Disorders of the respiratory system can be classified into four general areas:
Obstructive conditions (e.g., emphysema, bronchitis, asthma attacks)
Restrictive conditions (e.g., fibrosis, sarcoidosis, alveolar damage, pleural effusion)
Vascular diseases (e.g., pulmonary edema, pulmonary embolism, pulmonary hypertension)
Infectious, environmental and other "diseases" (e.g., pneumonia, tuberculosis, asbestosis, particulate pollutants): Coughing is of major importance, as it is the body's main method to remove dust, mucus, saliva, and other debris from the lungs. Inability to cough can lead to infection. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.
The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent pathogens from entering the body.
Disorders of the respiratory system are usually treated internally by a pulmonologist.
[edit] Plants
Plants use carbon dioxide gas in the process of photosynthesis, and then exhale oxygen gas, a waste product of photosynthesis. However, plants also sometimes respire as humans do, taking in oxygen and producing carbon dioxide.
Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes on the undersides of their leaves known as stomata (sing:stoma). However, most plants require little air.[citation needed] Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
Sympathetic Nervous System
Sympathetic nervous system
The sympathetic nervous system (SNS) is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilise the body's resources under stress; to induce the flight-or-fight response. It is, however, constantly active at a basal level in order to maintain homeostasis.[1]
Overview
Alongside the other components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. It is not consciously operated. Generally, it works to mobilise the body's resources for action under stress - as in the flight-or-fight response - and so may be thought to counteract the parasympathetic system, which generally works to promote maintenance of the body at rest. In truth, the functions of both systems are not so straightforward, but this is a useful rule of thumb.[1][2]
There are two groups of neurons involved in the transmission of any signal through the sympathetic system: pre- and post- ganglionic. The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord (levels T1 - L2, specifically) and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body.[3]
At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter which activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus postganglionic neurons - with two important exceptions - release noradrenaline, which activates adrenergic receptors on the peripheral target tissues. It is the activation of target tissue receptors which causes the effects associated with the sympathetic system.[4]
The two exceptions mentioned above are postganglionic neurones innervating sweat glands - which release acetylcholine for the activation of muscarinic receptors - and the adrenal medulla. The adrenal medulla develops in tandem with the sympathetic nervous system, and acts as a modified sympathetic ganglion: synapses occur between pre- and post- ganglionic neurons within it, but the post ganglionic neurons do not leave the medulla; instead they directly release noradrenaline and adrenaline into the blood.[5]
[edit] Function
Organ
Effect
Eye
Dilates pupil
Heart
Increases rate and force of contraction
Lungs
Dilates bronchioles
Digestive tract
Inhibits peristalsis
Kidney
Increases renin secretion
Penis
Promotes ejaculation
Examples of sympathetic system action on various organs.[5]
The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulatory function to things as diverse as pupil diameter, gut motility, and urinary output. It is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the fight-or-flight response. This response is also known as sympatho-adrenal response of the body, as the preganglionic sympathetic fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine, which activates the great secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the cardiovascular system is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines secreted from the adrenal medulla.
Some evolutionary theorists suggest that the sympathetic nervous system operated in early organisms to maintain survival as the sympathetic nervous system is responsible for priming the body for action.[6] One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.
[edit] Organization
Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in the intermediolateral cell column (or lateral horn), beginning at the first thoracic segment of the spinal cord and are thought to extend to the second or third lumbar segments. Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior rootlet/root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) which connect to the either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
In order to reach the target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
Presynaptic nerves' axons terminate in either the paravertebral ganglia or prevertebral ganglia. This can occur through one of four methods:
1. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve, and then ascends to a more superior paravertebral ganglion, where it synapses with the postsynaptic cell.
2. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve and synapses with the postsynaptic cell at that level.
3. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve, and then descends to a more inferior paravertebral ganglion, where it synapses with the postsynaptic cell.
4. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve and then descends to a prevertebral ganglion, where it synapses with the postsynaptic cell.
The postsynaptic cell then goes on to innervate the targeted end effector (ie gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) glands. In this case, presynaptic neurons pass through paraverterbral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the blood stream.
In the SNS and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the SNS are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.
The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which sends sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia (which send sympathetic fibers to the gut).
[edit] Information transmission
Messages travel through the SNS in a bidirectional flow. Efferent messages can trigger changes in different parts of the body simultaneously. For example, the sympathetic nervous system can accelerate heart rate; widen bronchial passages; decrease motility (movement) of the large intestine; constrict blood vessels; increase peristalsis in the esophagus; cause pupil dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure. Afferent messages carry sensations such as heat, cold, or pain.
The first synapse (in the sympathetic chain) is mediated by nicotinic receptors physiologically activated by acetylcholine, and the target synapse is mediated by adrenergic receptors physiologically activated by either noradrenaline (norepinephrine) or adrenaline (epinephrine). An exception is with sweat glands which receive sympathetic innervation but have muscarinic acetylcholine receptors which are normally characteristic of Parasympathetic nervous system. Another exception is with certain deep muscle blood vessels, which dilate (rather than constrict) with an increase in sympathetic tone.This is because of the presence of more beta2 receptors(rather than alpha1 which are frequently found on other vessels).
The sympathetic nervous system (SNS) is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilise the body's resources under stress; to induce the flight-or-fight response. It is, however, constantly active at a basal level in order to maintain homeostasis.[1]
Overview
Alongside the other components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. It is not consciously operated. Generally, it works to mobilise the body's resources for action under stress - as in the flight-or-fight response - and so may be thought to counteract the parasympathetic system, which generally works to promote maintenance of the body at rest. In truth, the functions of both systems are not so straightforward, but this is a useful rule of thumb.[1][2]
There are two groups of neurons involved in the transmission of any signal through the sympathetic system: pre- and post- ganglionic. The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord (levels T1 - L2, specifically) and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body.[3]
At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter which activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus postganglionic neurons - with two important exceptions - release noradrenaline, which activates adrenergic receptors on the peripheral target tissues. It is the activation of target tissue receptors which causes the effects associated with the sympathetic system.[4]
The two exceptions mentioned above are postganglionic neurones innervating sweat glands - which release acetylcholine for the activation of muscarinic receptors - and the adrenal medulla. The adrenal medulla develops in tandem with the sympathetic nervous system, and acts as a modified sympathetic ganglion: synapses occur between pre- and post- ganglionic neurons within it, but the post ganglionic neurons do not leave the medulla; instead they directly release noradrenaline and adrenaline into the blood.[5]
[edit] Function
Organ
Effect
Eye
Dilates pupil
Heart
Increases rate and force of contraction
Lungs
Dilates bronchioles
Digestive tract
Inhibits peristalsis
Kidney
Increases renin secretion
Penis
Promotes ejaculation
Examples of sympathetic system action on various organs.[5]
The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulatory function to things as diverse as pupil diameter, gut motility, and urinary output. It is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the fight-or-flight response. This response is also known as sympatho-adrenal response of the body, as the preganglionic sympathetic fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine, which activates the great secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the cardiovascular system is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines secreted from the adrenal medulla.
Some evolutionary theorists suggest that the sympathetic nervous system operated in early organisms to maintain survival as the sympathetic nervous system is responsible for priming the body for action.[6] One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.
[edit] Organization
Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in the intermediolateral cell column (or lateral horn), beginning at the first thoracic segment of the spinal cord and are thought to extend to the second or third lumbar segments. Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior rootlet/root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) which connect to the either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
In order to reach the target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
Presynaptic nerves' axons terminate in either the paravertebral ganglia or prevertebral ganglia. This can occur through one of four methods:
1. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve, and then ascends to a more superior paravertebral ganglion, where it synapses with the postsynaptic cell.
2. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve and synapses with the postsynaptic cell at that level.
3. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve, and then descends to a more inferior paravertebral ganglion, where it synapses with the postsynaptic cell.
4. The nerve enters the paravertebral ganglion at the level of its originating spinal nerve and then descends to a prevertebral ganglion, where it synapses with the postsynaptic cell.
The postsynaptic cell then goes on to innervate the targeted end effector (ie gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) glands. In this case, presynaptic neurons pass through paraverterbral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the blood stream.
In the SNS and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the SNS are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.
The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which sends sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia (which send sympathetic fibers to the gut).
[edit] Information transmission
Messages travel through the SNS in a bidirectional flow. Efferent messages can trigger changes in different parts of the body simultaneously. For example, the sympathetic nervous system can accelerate heart rate; widen bronchial passages; decrease motility (movement) of the large intestine; constrict blood vessels; increase peristalsis in the esophagus; cause pupil dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure. Afferent messages carry sensations such as heat, cold, or pain.
The first synapse (in the sympathetic chain) is mediated by nicotinic receptors physiologically activated by acetylcholine, and the target synapse is mediated by adrenergic receptors physiologically activated by either noradrenaline (norepinephrine) or adrenaline (epinephrine). An exception is with sweat glands which receive sympathetic innervation but have muscarinic acetylcholine receptors which are normally characteristic of Parasympathetic nervous system. Another exception is with certain deep muscle blood vessels, which dilate (rather than constrict) with an increase in sympathetic tone.This is because of the presence of more beta2 receptors(rather than alpha1 which are frequently found on other vessels).
Parasympathetic Nervous System
Parasympathetic nervous system
The parasympathetic nervous system (PSNS) is a division of the autonomic nervous system (ANS), along with the sympathetic nervous system (SNS) and enteric nervous system (ENS or "bowels NS"). The ANS is a subdivision of the peripheral nervous system (PNS). ANS sends fibers to three tissues: cardiac muscle, smooth muscle, or glandular tissue. This stimulation, sympathetic or parasympathetic, is to control smooth muscle contraction, regulate cardiac muscle, or stimulate or inhibit glandular secretion. The actions of the parasympathetic nervous system can be summarized as "rest, recovery, relaxation", as opposed to the "fight, flight, fright" effects of the sympathetic nervous system.
Relation to sympathetic nervous system
Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better understood as complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. A useful acronym to summarize the functions of the parasympathetic nervous system is SLUDD (salivation, lacrimation, urination, digestion and defecation).
[edit] Physical location
The parasympathetic nerves (PSN) are visceral, autonomic branches of the peripheral nervous system (PNS). The autonomic nervous system (ANS), which includes sympathetic and parasympathetic divisions, regulates the body's visceral organs via the innervation of three kinds of tissues: smooth muscle, cardiac muscle, and glands. The sympathetic and parasympathetic system work in tandem to create a synergistic stimulation that is not merely on or off, but has been described as a continuum depending upon how vigorously each division is attempting to carry out its actions. The regions of the body associated with the parasympathetic division of the ANS are in the cranial and sacral regions of the spinal cord. Because of its location the parasympathetic system is commonly referred to as having craniosacral outflow whereas the sympathetic system is referred to as thoracolumbar outflow (T1-L2 spinal nerves). In the cranium the PSN originate from cranial nerves CN III (oculomotor nerve), CN VII (facial nerve), CN IX (glossopharyngeal nerve) and CN X (vagus n.) In the sacral region of the body the PSN is derived from spinal nerves S2, S3 and S4, commonly referred to as the pelvic splanchnics.
Similar to the SN, the PSN follows a two-neuron efferent (motor signals leaving CNS) system that has both preganglionic and postganglionic neurons. In the cranium, preganglionic PSN (CN III, CN VII, and CN IX) arise from specific nuclei in the Central Nervous System (CNS) and synapse at one of four parasympathetic ganglia: ciliary, pterygopalatine, otic, or submandibular. From these four ganglia the PSN complete their journey to target tissues via CN V (trigeminal) branches (ophthalmic nerve CN V1, maxillary nerve CN V2, mandibular nerve CN V3). The vagus nerve does not participate in these cranial ganglion as most of its PSN fibers are destined for a broad array of ganglia on or near organs including the thoracic viscera (esophagus, trachea, heart, lungs) and abdominal viscera (stomach, pancreas, liver, kidneys) traveling all the way down to the midgut/hindgut junction just before the splenic flexure of the transverse colon. The pelvic splanchnic preganglionic nerve cell bodies arise in the ventral horn of the spinal cord and continue away from the CNS to synapse at an autonomic ganglion. The PSN ganglion, where the preganglionic neurons synapse, will be close to the organ of innervation (unlike the SN where the ganglion is typically farther away from the target organ). The two neuron system is only for efferent innervation. Afferent, unconscious sensations sent from the viscera to the CNS are done so in a one neuron tract.
The afferent parasympathetic sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. Like regular somatic sensory neurons, parasympathetic afferent cell bodies are located in the dorsal root ganglion. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain sensations to the CNS masked as referred pain. If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended your body will interpret the afferent pain stimulus as somatic in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.
[edit] Cranial Nerve Parasympathetic Paths and Control
The oculomotor nerve is responsible for several parasympathetic functions related to the eye. The oculomotor PNS fibers originate in the Edinger-Westphal nucleus in the CNS and travel through the superior orbital fissure to synapse in the ciliary ganglion located just behind the orbit (eye). From the ciliary ganglion the postganglionic PSN fibers leave via short ciliary nerve fibers, a continuation of the nasociliary nerve (a branch of ophthalmic division of the trigeminal nerve, CN V1). The short ciliary nerves innervate the orbit to control the ciliary muscle (responsible for accommodation) and the sphincter pupillae muscle which is responsible for miosis or constriction of the pupil (in response to light or accommodation).
The parasympathetic aspect of the facial nerve controls secretion of the sublingual and submandibular salivary glands, the lacrimal gland, and the glands associated with the nasal cavity. The preganglionic fibers originate within the CNS in the superior salivatory nucleus and leave as the intermediate nerve (which some consider a separate cranial nerve altogether) to connect with the facial nerve just distal (further out) to it surfacing the CNS. Just after the facial nerve geniculate ganglion (general sensory ganglion) in the temporal bone, the facial nerve gives off two separate parasympathetic nerves. The first is the greater petrosal nerve and the second is the chorda tympani. The greater petrosal nerve travels through the middle ear and eventually combines with the deep petrosal nerve (sympathetic fibers) to form the nerve of the pterygoid canal. The PSN fibers of the nerve of the pterygoid canal synapse at the pterygopalatine ganglion, which is closely associated with the maxillary division of the trigeminal nerve (CN V2). The postganglionic PSN fibers leave the pterygopalatine ganglion in several directions. One division leaves on the zygomatic division of CN V2 and travels on a communicating branch to unite with the lacrimal nerve (branch of the ophthalmic nerve of CN V1) before synapsing at the lacrimal gland. These PSN to the lacrimal gland control tear production.
A separate group of PSN leaving from the pterygopalatine ganglion are the descending palatine nerves (CN V2 branch) which include the greater and lesser palatine nerves. The greater palatine PSN synapse on the hard palate and regulate mucus glands located there. The lesser palatine nerve synapses at the soft palate and controls sparse taste receptors and mucus glands. Yet another set of divisions from the pterygopalatine ganglion are the posterior, superior, and inferior lateral nasal nerves; and the nasopalatine nerves (all branches of CN V2, maxillary division of the trigeminal nerve) that bring PSN to glands of the nasal mucosa. The second PSN branch that leaves the facial nerve is the chorda tympani. This nerve carries secretomotor fibers to the submandibular and sublingual glands. The chorda tympani travels through the middle ear and attaches to the lingual nerve (mandibular division of trigeminal, CN V3). After joining the lingual nerve the preganglionic fibers synapse at the submandibular ganglion and send postganglionic fibers to the sublingual and submandibular salivary glands.
The glossopharyngeal nerve, CNIX, has parasympathetic fibers that innervate the parotid salivary gland. The preganglionic fibers depart CNIX as the tympanic nerve and continue to the middle ear where they make up a tympanic plexus on the promontory of the tympanic membrane. The tympanic plexus of nerves rejoin and form the lesser petrosal nerve and exit through the foramen ovale to synapse at the otic ganglion. From the otic ganglion postganglionic parasympathetic fibers travel with the auriculotemporal nerve (mandibular branch of trigeminal, CN V3) to the parotid salivary gland.
The vagus nerve, named from the Latin word vagus means literally "Wandering", since the nerve controls such a broad range of target tissues, has PSN that originate in the dorsal nucleus of the vagus nerve and the nucleus ambiguus in the CNS. The vagus nerve is an unusual cranial PSN in that it doesn't join the trigeminal nerve in order to get to its target tissues. Another peculiarity is that the vagus has an autonomic ganglion associated with it at approximately the level of C1 vertebra. The vagus gives no PSN to the cranium. The vagus nerve is hard to track definitively due to its ubiquitous nature in the thorax and abdomen so the major contributions will be discussed. Several PSN nerves come off the vagus nerve as it enters the thorax. One nerve is the recurrent laryngeal nerve, which becomes the inferior laryngeal nerve. From the left vagus nerve the recurrent laryngeal nerve hooks around the aorta to travel back up to the larynx and proximal esophagus while, from the right vagus nerve, the recurrent laryngeal nerve hooks around the right subclavian artery to travel back up to the same location as its counterpart. These different paths are a direct result of embryological development of the circulatory system. Each recurrent laryngeal nerve supplies the trachea and the esophagus with parasympathetic secretomotor innervation for glands associated with them (and other fibers that are not PSN).
Another nerve that comes off the vagal nerves approximately at the level of entering the thorax are the cardiac nerves. These cardiac nerves go on to form cardiac and pulmonary plexuses around the heart and lungs. As the main vagus nerves continue into the thorax they become intimately linked with the esophagus and sympathetic nerves from the sympathetic trunks to form the esophageal plexus. This is very efficient as the major function of the vagus nerve from there on will be control of the gut smooth muscles and glands. As the esophageal plexus enter the abdomen through the esophageal hiatus anterior and posterior vagal trunks form. The vagal trunks then join with preaortic sympathetic ganglion around the aorta to disperse with the blood vessels and sympathetic nerves throughout the abdomen. The extent of the PSN in the abdomen include the pancreas, kidneys, liver, gall bladder, stomach and gut tube. The vagal contribution of PSN continues down the gut tube until the end of the midgut. The midgut ends 2/3 of the way across the transverse colon near the splenic flexure.[1]
[edit] Pelvic Splanchnic Control
The pelvic splanchnic nerves, S2-4, work in tandem to innervate the pelvic viscera. Unlike in the cranium, where one PSN was in charge of one particular tissue or region, for the most part the pelvic splanchnics each contribute fibers to pelvic viscera by first traveling to one or more plexuses before being dispersed to the target tissue. These plexuses are composed of mixed autonomic nerve fibers (PSN and SN) and include the vesical, prostatic, rectal, uterovaginal and inferior hypogastric plexus. The preganglionic neurons in the neurons do not synapse in named ganglion as in the cranium but rather in the walls of the tissues or organs that they innervate. The fiber paths are variable and each individual's autonomic nervous system in the pelvis is unique. The visceral tissues in the pelvis that the PSN control include: urinary bladder, ureters, urinary sphincter, anal sphincter, uterus, prostate, glands, vagina and penis. Unconsciously, the PSN will cause peristaltic movements of the ureters helping to move urine from the kidneys into the bladder and move feces down the intestinal tract and upon necessity, the PSN will help you excrete urine from the bladder or defaecate. Stimulation of the PSN will cause the detruser muscle (urinary bladder wall) to contract and simultaneously relax the internal sphincter urethrae muscle to relax allowing void of urine. Also, PSN stimulation to the internal anal sphincter will relax this muscle and allow you to have a bowel movement. There are other skeletal muscles involved with these processes but the PSN play a huge role in continence.
Another role that the PSN play in the pelvis is in sexual activity. In males, the cavernous nerves from the prostatic plexus stimulate smooth muscle in the fibrous trabeculae of the coiled helicene arteries to relax and allow blood to fill the corpora cavernosum and the corpus spongiosum of the penis, making it rigid to prepare for sexual activity. Upon emission of ejaculate, the sympathetics participate and cause peristalsis of the ductus deferens and closure of the internal urethral sphincter to prevent semen from entering the bladder. At the same time, parasympathetics cause peristalsis of the urethral muscle, and the pudendal nerve causes contraction of the bulbospongiosus (skeletal muscle is not via PSN), to forcibly emit the semen. During remission the penis becomes flaccid again. In the female, there is erectile tissue analogous to the male yet less substantial that plays a large role in sexual stimulation. The PSN cause release of secretions in the female that decrease friction. Also in the female, the parasympathetics innervate the fallopian tubes which helps peristaltic contractions and movement of the oocyte to the uterus for implantation. The secretions from the female genital tract aids in semen migration. The PSN (and SN to a lesser extent) play a huge role in reproduction.[2]
[edit] Clinical Significance
The parasympathetic nervous system promotes digestion and the synthesis of glycogen, and allows for normal function and behavior.
[edit] Receptors
The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter, although other peptides (such as cholecystokinin) may act on the PSNS as a neurotransmitter.[3][4] The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors. Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of postganglionic neurons. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.
[edit] Types of muscarinic receptors
The three main types of muscarinic receptors that are well characterised are:
The M1 muscarinic receptors (CHRM1) are located in the neural system.
The M2 muscarinic receptors (CHRM2) are located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the sinoatrial node (SA node) and atrioventricular node (AV node). Note, they have a minimal effect on the contractile forces of the ventricular muscle due to sparse innervation of the ventricles from the parasympathetic nervous system.
The M3 muscarinic receptors (CHRM3) are located at many places in the body, such as the smooth muscles of the blood vessels causing vasoconstriction, as well as the lungs causing bronchoconstriction. However, its net effect on blood vessels is vasodilation, as acetylcholine causes endothelial cells to produce nitric oxide, which diffuses to smooth muscle and results in vasodilation. They are also in the smooth muscles of the gastrointestinal tract (GIT), which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body.
The M4 muscarinic receptors: Postganglionic cholinergic nerves, possible CNS effects
The M5 muscarinic receptors: Possible effects on the CNS
The parasympathetic nervous system (PSNS) is a division of the autonomic nervous system (ANS), along with the sympathetic nervous system (SNS) and enteric nervous system (ENS or "bowels NS"). The ANS is a subdivision of the peripheral nervous system (PNS). ANS sends fibers to three tissues: cardiac muscle, smooth muscle, or glandular tissue. This stimulation, sympathetic or parasympathetic, is to control smooth muscle contraction, regulate cardiac muscle, or stimulate or inhibit glandular secretion. The actions of the parasympathetic nervous system can be summarized as "rest, recovery, relaxation", as opposed to the "fight, flight, fright" effects of the sympathetic nervous system.
Relation to sympathetic nervous system
Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better understood as complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. A useful acronym to summarize the functions of the parasympathetic nervous system is SLUDD (salivation, lacrimation, urination, digestion and defecation).
[edit] Physical location
The parasympathetic nerves (PSN) are visceral, autonomic branches of the peripheral nervous system (PNS). The autonomic nervous system (ANS), which includes sympathetic and parasympathetic divisions, regulates the body's visceral organs via the innervation of three kinds of tissues: smooth muscle, cardiac muscle, and glands. The sympathetic and parasympathetic system work in tandem to create a synergistic stimulation that is not merely on or off, but has been described as a continuum depending upon how vigorously each division is attempting to carry out its actions. The regions of the body associated with the parasympathetic division of the ANS are in the cranial and sacral regions of the spinal cord. Because of its location the parasympathetic system is commonly referred to as having craniosacral outflow whereas the sympathetic system is referred to as thoracolumbar outflow (T1-L2 spinal nerves). In the cranium the PSN originate from cranial nerves CN III (oculomotor nerve), CN VII (facial nerve), CN IX (glossopharyngeal nerve) and CN X (vagus n.) In the sacral region of the body the PSN is derived from spinal nerves S2, S3 and S4, commonly referred to as the pelvic splanchnics.
Similar to the SN, the PSN follows a two-neuron efferent (motor signals leaving CNS) system that has both preganglionic and postganglionic neurons. In the cranium, preganglionic PSN (CN III, CN VII, and CN IX) arise from specific nuclei in the Central Nervous System (CNS) and synapse at one of four parasympathetic ganglia: ciliary, pterygopalatine, otic, or submandibular. From these four ganglia the PSN complete their journey to target tissues via CN V (trigeminal) branches (ophthalmic nerve CN V1, maxillary nerve CN V2, mandibular nerve CN V3). The vagus nerve does not participate in these cranial ganglion as most of its PSN fibers are destined for a broad array of ganglia on or near organs including the thoracic viscera (esophagus, trachea, heart, lungs) and abdominal viscera (stomach, pancreas, liver, kidneys) traveling all the way down to the midgut/hindgut junction just before the splenic flexure of the transverse colon. The pelvic splanchnic preganglionic nerve cell bodies arise in the ventral horn of the spinal cord and continue away from the CNS to synapse at an autonomic ganglion. The PSN ganglion, where the preganglionic neurons synapse, will be close to the organ of innervation (unlike the SN where the ganglion is typically farther away from the target organ). The two neuron system is only for efferent innervation. Afferent, unconscious sensations sent from the viscera to the CNS are done so in a one neuron tract.
The afferent parasympathetic sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. Like regular somatic sensory neurons, parasympathetic afferent cell bodies are located in the dorsal root ganglion. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain sensations to the CNS masked as referred pain. If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended your body will interpret the afferent pain stimulus as somatic in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.
[edit] Cranial Nerve Parasympathetic Paths and Control
The oculomotor nerve is responsible for several parasympathetic functions related to the eye. The oculomotor PNS fibers originate in the Edinger-Westphal nucleus in the CNS and travel through the superior orbital fissure to synapse in the ciliary ganglion located just behind the orbit (eye). From the ciliary ganglion the postganglionic PSN fibers leave via short ciliary nerve fibers, a continuation of the nasociliary nerve (a branch of ophthalmic division of the trigeminal nerve, CN V1). The short ciliary nerves innervate the orbit to control the ciliary muscle (responsible for accommodation) and the sphincter pupillae muscle which is responsible for miosis or constriction of the pupil (in response to light or accommodation).
The parasympathetic aspect of the facial nerve controls secretion of the sublingual and submandibular salivary glands, the lacrimal gland, and the glands associated with the nasal cavity. The preganglionic fibers originate within the CNS in the superior salivatory nucleus and leave as the intermediate nerve (which some consider a separate cranial nerve altogether) to connect with the facial nerve just distal (further out) to it surfacing the CNS. Just after the facial nerve geniculate ganglion (general sensory ganglion) in the temporal bone, the facial nerve gives off two separate parasympathetic nerves. The first is the greater petrosal nerve and the second is the chorda tympani. The greater petrosal nerve travels through the middle ear and eventually combines with the deep petrosal nerve (sympathetic fibers) to form the nerve of the pterygoid canal. The PSN fibers of the nerve of the pterygoid canal synapse at the pterygopalatine ganglion, which is closely associated with the maxillary division of the trigeminal nerve (CN V2). The postganglionic PSN fibers leave the pterygopalatine ganglion in several directions. One division leaves on the zygomatic division of CN V2 and travels on a communicating branch to unite with the lacrimal nerve (branch of the ophthalmic nerve of CN V1) before synapsing at the lacrimal gland. These PSN to the lacrimal gland control tear production.
A separate group of PSN leaving from the pterygopalatine ganglion are the descending palatine nerves (CN V2 branch) which include the greater and lesser palatine nerves. The greater palatine PSN synapse on the hard palate and regulate mucus glands located there. The lesser palatine nerve synapses at the soft palate and controls sparse taste receptors and mucus glands. Yet another set of divisions from the pterygopalatine ganglion are the posterior, superior, and inferior lateral nasal nerves; and the nasopalatine nerves (all branches of CN V2, maxillary division of the trigeminal nerve) that bring PSN to glands of the nasal mucosa. The second PSN branch that leaves the facial nerve is the chorda tympani. This nerve carries secretomotor fibers to the submandibular and sublingual glands. The chorda tympani travels through the middle ear and attaches to the lingual nerve (mandibular division of trigeminal, CN V3). After joining the lingual nerve the preganglionic fibers synapse at the submandibular ganglion and send postganglionic fibers to the sublingual and submandibular salivary glands.
The glossopharyngeal nerve, CNIX, has parasympathetic fibers that innervate the parotid salivary gland. The preganglionic fibers depart CNIX as the tympanic nerve and continue to the middle ear where they make up a tympanic plexus on the promontory of the tympanic membrane. The tympanic plexus of nerves rejoin and form the lesser petrosal nerve and exit through the foramen ovale to synapse at the otic ganglion. From the otic ganglion postganglionic parasympathetic fibers travel with the auriculotemporal nerve (mandibular branch of trigeminal, CN V3) to the parotid salivary gland.
The vagus nerve, named from the Latin word vagus means literally "Wandering", since the nerve controls such a broad range of target tissues, has PSN that originate in the dorsal nucleus of the vagus nerve and the nucleus ambiguus in the CNS. The vagus nerve is an unusual cranial PSN in that it doesn't join the trigeminal nerve in order to get to its target tissues. Another peculiarity is that the vagus has an autonomic ganglion associated with it at approximately the level of C1 vertebra. The vagus gives no PSN to the cranium. The vagus nerve is hard to track definitively due to its ubiquitous nature in the thorax and abdomen so the major contributions will be discussed. Several PSN nerves come off the vagus nerve as it enters the thorax. One nerve is the recurrent laryngeal nerve, which becomes the inferior laryngeal nerve. From the left vagus nerve the recurrent laryngeal nerve hooks around the aorta to travel back up to the larynx and proximal esophagus while, from the right vagus nerve, the recurrent laryngeal nerve hooks around the right subclavian artery to travel back up to the same location as its counterpart. These different paths are a direct result of embryological development of the circulatory system. Each recurrent laryngeal nerve supplies the trachea and the esophagus with parasympathetic secretomotor innervation for glands associated with them (and other fibers that are not PSN).
Another nerve that comes off the vagal nerves approximately at the level of entering the thorax are the cardiac nerves. These cardiac nerves go on to form cardiac and pulmonary plexuses around the heart and lungs. As the main vagus nerves continue into the thorax they become intimately linked with the esophagus and sympathetic nerves from the sympathetic trunks to form the esophageal plexus. This is very efficient as the major function of the vagus nerve from there on will be control of the gut smooth muscles and glands. As the esophageal plexus enter the abdomen through the esophageal hiatus anterior and posterior vagal trunks form. The vagal trunks then join with preaortic sympathetic ganglion around the aorta to disperse with the blood vessels and sympathetic nerves throughout the abdomen. The extent of the PSN in the abdomen include the pancreas, kidneys, liver, gall bladder, stomach and gut tube. The vagal contribution of PSN continues down the gut tube until the end of the midgut. The midgut ends 2/3 of the way across the transverse colon near the splenic flexure.[1]
[edit] Pelvic Splanchnic Control
The pelvic splanchnic nerves, S2-4, work in tandem to innervate the pelvic viscera. Unlike in the cranium, where one PSN was in charge of one particular tissue or region, for the most part the pelvic splanchnics each contribute fibers to pelvic viscera by first traveling to one or more plexuses before being dispersed to the target tissue. These plexuses are composed of mixed autonomic nerve fibers (PSN and SN) and include the vesical, prostatic, rectal, uterovaginal and inferior hypogastric plexus. The preganglionic neurons in the neurons do not synapse in named ganglion as in the cranium but rather in the walls of the tissues or organs that they innervate. The fiber paths are variable and each individual's autonomic nervous system in the pelvis is unique. The visceral tissues in the pelvis that the PSN control include: urinary bladder, ureters, urinary sphincter, anal sphincter, uterus, prostate, glands, vagina and penis. Unconsciously, the PSN will cause peristaltic movements of the ureters helping to move urine from the kidneys into the bladder and move feces down the intestinal tract and upon necessity, the PSN will help you excrete urine from the bladder or defaecate. Stimulation of the PSN will cause the detruser muscle (urinary bladder wall) to contract and simultaneously relax the internal sphincter urethrae muscle to relax allowing void of urine. Also, PSN stimulation to the internal anal sphincter will relax this muscle and allow you to have a bowel movement. There are other skeletal muscles involved with these processes but the PSN play a huge role in continence.
Another role that the PSN play in the pelvis is in sexual activity. In males, the cavernous nerves from the prostatic plexus stimulate smooth muscle in the fibrous trabeculae of the coiled helicene arteries to relax and allow blood to fill the corpora cavernosum and the corpus spongiosum of the penis, making it rigid to prepare for sexual activity. Upon emission of ejaculate, the sympathetics participate and cause peristalsis of the ductus deferens and closure of the internal urethral sphincter to prevent semen from entering the bladder. At the same time, parasympathetics cause peristalsis of the urethral muscle, and the pudendal nerve causes contraction of the bulbospongiosus (skeletal muscle is not via PSN), to forcibly emit the semen. During remission the penis becomes flaccid again. In the female, there is erectile tissue analogous to the male yet less substantial that plays a large role in sexual stimulation. The PSN cause release of secretions in the female that decrease friction. Also in the female, the parasympathetics innervate the fallopian tubes which helps peristaltic contractions and movement of the oocyte to the uterus for implantation. The secretions from the female genital tract aids in semen migration. The PSN (and SN to a lesser extent) play a huge role in reproduction.[2]
[edit] Clinical Significance
The parasympathetic nervous system promotes digestion and the synthesis of glycogen, and allows for normal function and behavior.
[edit] Receptors
The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter, although other peptides (such as cholecystokinin) may act on the PSNS as a neurotransmitter.[3][4] The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors. Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of postganglionic neurons. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.
[edit] Types of muscarinic receptors
The three main types of muscarinic receptors that are well characterised are:
The M1 muscarinic receptors (CHRM1) are located in the neural system.
The M2 muscarinic receptors (CHRM2) are located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the sinoatrial node (SA node) and atrioventricular node (AV node). Note, they have a minimal effect on the contractile forces of the ventricular muscle due to sparse innervation of the ventricles from the parasympathetic nervous system.
The M3 muscarinic receptors (CHRM3) are located at many places in the body, such as the smooth muscles of the blood vessels causing vasoconstriction, as well as the lungs causing bronchoconstriction. However, its net effect on blood vessels is vasodilation, as acetylcholine causes endothelial cells to produce nitric oxide, which diffuses to smooth muscle and results in vasodilation. They are also in the smooth muscles of the gastrointestinal tract (GIT), which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body.
The M4 muscarinic receptors: Postganglionic cholinergic nerves, possible CNS effects
The M5 muscarinic receptors: Possible effects on the CNS
Bryophyte
Bryophyte
Bryophytes are all embryophytes ('land plants') that are non-vascular:[1] they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids.[2] They neither have flowers nor produce seeds, reproducing via spores. The term bryophyte comes from Greek βρύον - bryon, "tree-moss, oyster-green" + φυτόν - fyton "plant".
Bryophyte classification
Mosses are one group of bryophytes.
The bryophytes (or non-tracheophytes) do not form a monophyletic group[3] but consist of three groups, the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses).[4] Originally the three groups were brought together as the three classes of division Bryophyta. However, since the three groups of bryophytes form a paraphyletic group, they now are placed in three separate divisions.
Two hypotheses on the phylogeny of land plants (embryophyta).
Modern studies of the land plants generally show one of two patterns.
In one of these patterns, the liverworts were the first to diverge, followed by the hornworts, while the mosses are the closest living relatives of the polysporangiates (which include the vascular plants).[5]
In the other pattern, the hornworts were the first to diverge, followed by the vascular plants, while the mosses are the closest living relatives of the liverworts.[citation needed]
[edit] Bryophyte sexuality
These plants are generally gametophyte-oriented; that is, the normal plant is the haploid gametophyte,[6] with the only diploid structure being the sporangium in season. As a result, bryophyte sexuality is very different from that of other plants. There are two basic categories of sexuality in bryophytes:
Dioicous bryophytes produce only antheridia (male organs) or archegonia (female organs) on a single plant body.
Monoicous bryophytes produce both antheridia and archegonia on the same plant body.
Some bryophyte species may be either monoicous or dioicous depending on environmental conditions. Other species grow exclusively with one type of sexuality.
Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte plant bears one or both kinds of gametophyte. Those terms apply only to seed plants.
[edit] Bryophyte life cycle
Dispersal in bryophytes is via spores; they neither have flowers nor produce seeds. Bryophytes do produce gametes that fuse to form a zygote, which in turn develops into an embryo, but this is not contained in a seed as in gymnosperms and angiosperms.
Moss
Mosses are small, soft plants that are typically 1–10 cm (0.4-4 in) tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems. At certain times mosses produce spore capsules which may appear as beak-like capsules borne aloft on thin stalks.
There are approximately 12,000 species of moss classified in the Bryophyta.[2] The division Bryophyta formerly included not only mosses, but also liverworts and hornworts. These other two groups of bryophytes now are often placed in their own divisions.
Physical characteristics
Description
Botanically, mosses are bryophytes, or non-vascular plants. They can be distinguished from the apparently similar liverworts (Marchantiophyta or Hepaticae) by their multi-cellular rhizoids. Other differences are not universal for all mosses and all liverworts, but the presence of clearly differentiated "stem" and "leaves", the lack of deeply lobed or segmented leaves, and the absence of leaves arranged in three ranks, all point to the plant being a moss.
In addition to lacking a vascular system, mosses have a gametophyte-dominant life cycle, i.e. the plant's cells are haploid for most of its life cycle. Sporophytes (i.e. the diploid body) are short-lived and dependent on the gametophyte. This is in contrast to the pattern exhibited by most "higher" plants and by most animals. In seed plants, for example, the haploid generation is represented by the pollen and the ovule, whilst the diploid generation is the familiar flowering plant.
Life cycle
Most kinds of plants have two sets of chromosomes in their vegetative cells and are said to be diploid, i.e. each chromosome has a partner that contains the same, or similar, genetic information. By contrast, mosses and other bryophytes have only a single set of chromosomes and so are haploid (i.e. each chromosome exists in a unique copy within the cell). There are periods in the moss life cycle when they do have a double set of paired chromosomes, but this happens only during the sporophyte stage.
Life cycle of a typical moss (Polytrichum commune)
The life of a moss starts from a haploid spore. The spore germinates to produce a protonema (pl. protonemata), which is either a mass of thread-like filaments or thalloid (flat and thallus-like). Moss protonemata typically look like a thin green felt, and may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable surface. This is a transitory stage in the life of a moss, but from the protonema grows the gametophore ("gamete-bearer") that is structurally differentiated into stems and leaves. A single mat of protonemata may develop several gametophore shoots, resulting in a clump of moss.
From the tips of the gametophore stems or branches develop the sex organs of the mosses. The female organs are known as archegonia (sing. archegonium) and are protected by a group of modified leaves known as the perichaetum (plural, perichaeta). The archegonia are small flask-shaped clumps of cells with an open neck (venter) down which the male sperm swim. The male organs are known as antheridia (sing. antheridium) and are enclosed by modified leaves called the perigonium (pl. perigonia). The surrounding leaves in some mosses form a splash cup, allowing the sperm contained in the cup to be splashed to neighboring stalks by falling water droplets.
Mosses can be either dioicous (compare dioecious in seed plants) or monoicous (compare monoecious). In dioicous mosses, male and female sex organs are borne on different gametophyte plants. In monoicous (also called autoicous) mosses, both are borne on the same plant. In the presence of water, sperm from the antheridia swim to the archegonia and fertilisation occurs, leading to the production of a diploid sporophyte. The sperm of mosses is biflagellate, i.e. they have two flagellae that aid in propulsion. Since the sperm must swim to the archegonium, fertilisation cannot occur without water. After fertilisation, the immature sporophyte pushes its way out of the archegonial venter. It takes about a quarter to half a year for the sporophyte to mature. The sporophyte body comprises a long stalk, called a seta, and a capsule capped by a cap called the operculum. The capsule and operculum are in turn sheathed by a haploid calyptra which is the remains of the archegonial venter. The calyptra usually falls off when the capsule is mature. Within the capsule, spore-producing cells undergo meiosis to form haploid spores, upon which the cycle can start again. The mouth of the capsule is usually ringed by a set of teeth called peristome. This may be absent in some mosses.
In some mosses, e.g. Ulota phyllantha, green vegetative structures called gemmae are produced on leaves or branches, which can break off and form new plants without the need to go through the cycle of fertilization. This is a means of asexual reproduction, and the genetically identical units can lead to the formation of clonal populations.
Classification
Traditionally, mosses were grouped with the liverworts and hornworts in the Division Bryophyta (bryophytes), within which the mosses made up the class Musci. This definition of Bryophyta, however, is paraphyletic and now tends to be split up into three divisions. In such a system, the Division Bryophyta contains exclusively mosses.
The mosses are grouped as a single division, now named Bryophyta, and divided into eight classes:
division Bryophyta
class Takakiopsida
class Sphagnopsida
class Andreaeopsida
class Andreaeobryopsida
class Oedipodiopsida
class Polytrichopsida
class Tetraphidopsida
class Bryopsida
liverworts
hornworts
vascular plants
Bryophyta
Takakiopsida
Sphagnopsida
Andreaeopsida
Andreaeobryopsida
Oedipodiopsida
Tetraphidopsida
Polytrichopsida
Bryopsida
The current phylogeny and composition of the Bryophyta.[2][3]
Moss in the Allegheny National Forest, Pennsylvania, USA.
Six of the eight classes contain only one or two genera each. Polytrichopsida includes 23 genera, and Bryopsida includes the majority of moss diversity with over 95% of moss species belonging to this class.
The Sphagnopsida, the peat-mosses, comprise the two living genera Ambuchanania and Sphagnum, as well as fossil taxa. However, the genus Sphagnum is a diverse, widespread, and economically important one. These large mosses form extensive acidic bogs in peat swamps. The leaves of Sphagnum have large dead cells alternating with living photosynthetic cells. The dead cells help to store water. Aside from this character, the unique branching, thallose (flat and expanded) protonema, and explosively rupturing sporangium place it apart from other mosses.
Andreaeopsida and Andreaeobryopsida are distinguished by the biseriate (two rows of cells) rhizoids, multiseriate (many rows of cells) protonema, and sporangium that splits along longitudinal lines. Most mosses have capsules that open at the top.
Polytrichopsida have leaves with sets of parallel lamellae, flaps of chloroplast-containing cells that look like the fins on a heat sink. These carry out photosynthesis and may help to conserve moisture by partially enclosing the gas exchange surfaces. The Polytrichopsida differ from other mosses in other details of their development and anatomy too, and can also become larger than most other mosses, with e.g. Polytrichum commune forming cushions up to 40 cm (16 in) high. The tallest land moss, a member of the Polytrichidae is probably Dawsonia superba, a native to New Zealand and other parts of Australasia.
They appear to be the closest living relatives of the vascular plants.
Red moss capsules, a winter native of the Yorkshire Dales moorland.
Geological history
The fossil record of moss is sparse, due to their soft-walled and fragile nature. Unambiguous moss fossils have been recovered from as early as the Permian of Antarctica and Russia, and a case is put forwards for Carboniferous mosses.[4] It has further been claimed that tube-like fossils from the Silurian are the macerated remains of moss calyptræ.[5]
Habitat
Dense moss colonies in a cool coastal forest
A closeup of moss on a rock
Young sporophytes of the common moss Tortula muralis (wall screw-moss)
A small clump of moss.
Mosses are found chiefly in areas of dampness and low light. Mosses are common in wooded areas and at the edges of streams. Mosses are also found in cracks between paving stones in damp city streets. Some types have adapted to urban conditions and are found only in cities. A few species are wholly aquatic, such as Fontinalis antipyretica, and others such as Sphagnum inhabit bogs, marshes and very slow-moving waterways. Such aquatic or semi-aquatic mosses can greatly exceed the normal range of lengths seen in terrestrial mosses. Individual plants 20–30 cm (8-12 in) or more long are common in Sphagnum species for example.
Wherever they occur, mosses require moisture to survive because of the small size and thinness of tissues, lack of cuticle (waxy covering to prevent water loss), and the need for liquid water to complete fertilisation. Some mosses can survive desiccation, returning to life within a few hours of rehydration.
In northern latitudes, the north side of trees and rocks will generally have more moss on average than other sides (though south-side outcroppings are not unknown). This is assumed to be because of the lack of sufficient water for reproduction on the sun-facing side of trees. South of the equator the reverse is true. In deep forests where sunlight does not penetrate, mosses grow equally well on all sides of the tree trunk.[citation needed]
Cultivation
Moss is considered a weed in grass lawns, but is deliberately encouraged to grow under aesthetic principles exemplified by Japanese gardening. In old temple gardens, moss can carpet a forest scene. Moss is thought to add a sense of calm, age, and stillness to a garden scene. Rules of cultivation are not widely established. Moss collections are quite often begun using samples transplanted from the wild in a water-retaining bag. However, specific species of moss can be extremely difficult to maintain away from their natural sites with their unique combinations of light, humidity, shelter from wind, etc.
Growing moss from spores is even less controlled. Moss spores fall in a constant rain on exposed surfaces; those surfaces which are hospitable to a certain species of moss will typically be colonised by that moss within a few years of exposure to wind and rain. Materials which are porous and moisture retentive, such as brick, wood, and certain coarse concrete mixtures are hospitable to moss. Surfaces can also be prepared with acidic substances, including buttermilk, yogurt, urine, and gently puréed mixtures of moss samples, water and ericaceous compost.
Inhibiting moss growth
Moss growth can be inhibited by a number of methods:
Decreasing availability of water through drainage or direct application changes.
Increasing direct sunlight.
Increasing number and resources available for competitive plants like grasses.
Increasing the soil pH with the application of lime.
Heavy traffic or manually disturbing the moss bed with a rake will also inhibit moss growth.
The application of products containing ferrous sulfate or ferrous ammonium sulfate will kill moss, these ingredients are typically in commercial moss control products and fertilizers. Sulfur and Iron are essential nutrients for some competing plants like grasses. Killing moss will not prevent regrowth unless conditions favorable to their growth are changed.[6]
Mossery
A passing fad for moss-collecting in the late 19th century led to the establishment of mosseries in many British and American gardens. The mossery is typically constructed out of slatted wood, with a flat roof, open to the north side (maintaining shade). Samples of moss were installed in the cracks between wood slats. The whole mossery would then be regularly moistened to maintain growth.
Commercial use
There is a substantial market in mosses gathered from the wild. The uses for intact moss are principally in the florist trade and for home decoration. Decaying moss in the genus Sphagnum is also the major component of peat, which is "mined" for use as a fuel, as a horticultural soil additive, and in smoking malt in the production of Scotch whisky.
Sphagnum moss, generally the species cristatum and subnitens, is harvested while still growing and is dried out to be used in nurseries and horticulture as a plant growing medium. The practice of harvesting peat moss should not be confused with the harvesting of moss peat.
Peat moss can be harvested on a sustainable basis and managed so that regrowth is allowed, whereas the harvesting of moss peat is generally considered to cause significant environmental damage as the peat is stripped with little or no chance of recovery.
In World War II, Sphagnum mosses were used as first-aid dressings on soldiers' wounds, as these mosses are highly absorbent and have mild antibacterial properties. Some early people used it as a diaper due to its high absorbency.[citation needed]
In rural UK, Fontinalis antipyretica was traditionally used to extinguish fires as it could be found in substantial quantities in slow-moving rivers and the moss retained large volumes of water which helped extinguish the flames. This historical use is reflected in its specific Latin/Greek name, the approximate meaning of which is "against fire".
In Finland, peat mosses have been used to make bread during famines.[citation needed]
In Mexico, Moss is used as a Christmas decoration.
Moss photobioreactor with Physcomitrella patens
Physcomitrella patens is increasingly used in biotechnology. Prominent examples are the identification of moss genes with implications for crop improvement or human health [7] and the safe production of complex biopharmaceuticals in the moss bioreactor, developed by Ralf Reski and his co-workers [8].
Bryophytes are all embryophytes ('land plants') that are non-vascular:[1] they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids.[2] They neither have flowers nor produce seeds, reproducing via spores. The term bryophyte comes from Greek βρύον - bryon, "tree-moss, oyster-green" + φυτόν - fyton "plant".
Bryophyte classification
Mosses are one group of bryophytes.
The bryophytes (or non-tracheophytes) do not form a monophyletic group[3] but consist of three groups, the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses).[4] Originally the three groups were brought together as the three classes of division Bryophyta. However, since the three groups of bryophytes form a paraphyletic group, they now are placed in three separate divisions.
Two hypotheses on the phylogeny of land plants (embryophyta).
Modern studies of the land plants generally show one of two patterns.
In one of these patterns, the liverworts were the first to diverge, followed by the hornworts, while the mosses are the closest living relatives of the polysporangiates (which include the vascular plants).[5]
In the other pattern, the hornworts were the first to diverge, followed by the vascular plants, while the mosses are the closest living relatives of the liverworts.[citation needed]
[edit] Bryophyte sexuality
These plants are generally gametophyte-oriented; that is, the normal plant is the haploid gametophyte,[6] with the only diploid structure being the sporangium in season. As a result, bryophyte sexuality is very different from that of other plants. There are two basic categories of sexuality in bryophytes:
Dioicous bryophytes produce only antheridia (male organs) or archegonia (female organs) on a single plant body.
Monoicous bryophytes produce both antheridia and archegonia on the same plant body.
Some bryophyte species may be either monoicous or dioicous depending on environmental conditions. Other species grow exclusively with one type of sexuality.
Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte plant bears one or both kinds of gametophyte. Those terms apply only to seed plants.
[edit] Bryophyte life cycle
Dispersal in bryophytes is via spores; they neither have flowers nor produce seeds. Bryophytes do produce gametes that fuse to form a zygote, which in turn develops into an embryo, but this is not contained in a seed as in gymnosperms and angiosperms.
Moss
Mosses are small, soft plants that are typically 1–10 cm (0.4-4 in) tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems. At certain times mosses produce spore capsules which may appear as beak-like capsules borne aloft on thin stalks.
There are approximately 12,000 species of moss classified in the Bryophyta.[2] The division Bryophyta formerly included not only mosses, but also liverworts and hornworts. These other two groups of bryophytes now are often placed in their own divisions.
Physical characteristics
Description
Botanically, mosses are bryophytes, or non-vascular plants. They can be distinguished from the apparently similar liverworts (Marchantiophyta or Hepaticae) by their multi-cellular rhizoids. Other differences are not universal for all mosses and all liverworts, but the presence of clearly differentiated "stem" and "leaves", the lack of deeply lobed or segmented leaves, and the absence of leaves arranged in three ranks, all point to the plant being a moss.
In addition to lacking a vascular system, mosses have a gametophyte-dominant life cycle, i.e. the plant's cells are haploid for most of its life cycle. Sporophytes (i.e. the diploid body) are short-lived and dependent on the gametophyte. This is in contrast to the pattern exhibited by most "higher" plants and by most animals. In seed plants, for example, the haploid generation is represented by the pollen and the ovule, whilst the diploid generation is the familiar flowering plant.
Life cycle
Most kinds of plants have two sets of chromosomes in their vegetative cells and are said to be diploid, i.e. each chromosome has a partner that contains the same, or similar, genetic information. By contrast, mosses and other bryophytes have only a single set of chromosomes and so are haploid (i.e. each chromosome exists in a unique copy within the cell). There are periods in the moss life cycle when they do have a double set of paired chromosomes, but this happens only during the sporophyte stage.
Life cycle of a typical moss (Polytrichum commune)
The life of a moss starts from a haploid spore. The spore germinates to produce a protonema (pl. protonemata), which is either a mass of thread-like filaments or thalloid (flat and thallus-like). Moss protonemata typically look like a thin green felt, and may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable surface. This is a transitory stage in the life of a moss, but from the protonema grows the gametophore ("gamete-bearer") that is structurally differentiated into stems and leaves. A single mat of protonemata may develop several gametophore shoots, resulting in a clump of moss.
From the tips of the gametophore stems or branches develop the sex organs of the mosses. The female organs are known as archegonia (sing. archegonium) and are protected by a group of modified leaves known as the perichaetum (plural, perichaeta). The archegonia are small flask-shaped clumps of cells with an open neck (venter) down which the male sperm swim. The male organs are known as antheridia (sing. antheridium) and are enclosed by modified leaves called the perigonium (pl. perigonia). The surrounding leaves in some mosses form a splash cup, allowing the sperm contained in the cup to be splashed to neighboring stalks by falling water droplets.
Mosses can be either dioicous (compare dioecious in seed plants) or monoicous (compare monoecious). In dioicous mosses, male and female sex organs are borne on different gametophyte plants. In monoicous (also called autoicous) mosses, both are borne on the same plant. In the presence of water, sperm from the antheridia swim to the archegonia and fertilisation occurs, leading to the production of a diploid sporophyte. The sperm of mosses is biflagellate, i.e. they have two flagellae that aid in propulsion. Since the sperm must swim to the archegonium, fertilisation cannot occur without water. After fertilisation, the immature sporophyte pushes its way out of the archegonial venter. It takes about a quarter to half a year for the sporophyte to mature. The sporophyte body comprises a long stalk, called a seta, and a capsule capped by a cap called the operculum. The capsule and operculum are in turn sheathed by a haploid calyptra which is the remains of the archegonial venter. The calyptra usually falls off when the capsule is mature. Within the capsule, spore-producing cells undergo meiosis to form haploid spores, upon which the cycle can start again. The mouth of the capsule is usually ringed by a set of teeth called peristome. This may be absent in some mosses.
In some mosses, e.g. Ulota phyllantha, green vegetative structures called gemmae are produced on leaves or branches, which can break off and form new plants without the need to go through the cycle of fertilization. This is a means of asexual reproduction, and the genetically identical units can lead to the formation of clonal populations.
Classification
Traditionally, mosses were grouped with the liverworts and hornworts in the Division Bryophyta (bryophytes), within which the mosses made up the class Musci. This definition of Bryophyta, however, is paraphyletic and now tends to be split up into three divisions. In such a system, the Division Bryophyta contains exclusively mosses.
The mosses are grouped as a single division, now named Bryophyta, and divided into eight classes:
division Bryophyta
class Takakiopsida
class Sphagnopsida
class Andreaeopsida
class Andreaeobryopsida
class Oedipodiopsida
class Polytrichopsida
class Tetraphidopsida
class Bryopsida
liverworts
hornworts
vascular plants
Bryophyta
Takakiopsida
Sphagnopsida
Andreaeopsida
Andreaeobryopsida
Oedipodiopsida
Tetraphidopsida
Polytrichopsida
Bryopsida
The current phylogeny and composition of the Bryophyta.[2][3]
Moss in the Allegheny National Forest, Pennsylvania, USA.
Six of the eight classes contain only one or two genera each. Polytrichopsida includes 23 genera, and Bryopsida includes the majority of moss diversity with over 95% of moss species belonging to this class.
The Sphagnopsida, the peat-mosses, comprise the two living genera Ambuchanania and Sphagnum, as well as fossil taxa. However, the genus Sphagnum is a diverse, widespread, and economically important one. These large mosses form extensive acidic bogs in peat swamps. The leaves of Sphagnum have large dead cells alternating with living photosynthetic cells. The dead cells help to store water. Aside from this character, the unique branching, thallose (flat and expanded) protonema, and explosively rupturing sporangium place it apart from other mosses.
Andreaeopsida and Andreaeobryopsida are distinguished by the biseriate (two rows of cells) rhizoids, multiseriate (many rows of cells) protonema, and sporangium that splits along longitudinal lines. Most mosses have capsules that open at the top.
Polytrichopsida have leaves with sets of parallel lamellae, flaps of chloroplast-containing cells that look like the fins on a heat sink. These carry out photosynthesis and may help to conserve moisture by partially enclosing the gas exchange surfaces. The Polytrichopsida differ from other mosses in other details of their development and anatomy too, and can also become larger than most other mosses, with e.g. Polytrichum commune forming cushions up to 40 cm (16 in) high. The tallest land moss, a member of the Polytrichidae is probably Dawsonia superba, a native to New Zealand and other parts of Australasia.
They appear to be the closest living relatives of the vascular plants.
Red moss capsules, a winter native of the Yorkshire Dales moorland.
Geological history
The fossil record of moss is sparse, due to their soft-walled and fragile nature. Unambiguous moss fossils have been recovered from as early as the Permian of Antarctica and Russia, and a case is put forwards for Carboniferous mosses.[4] It has further been claimed that tube-like fossils from the Silurian are the macerated remains of moss calyptræ.[5]
Habitat
Dense moss colonies in a cool coastal forest
A closeup of moss on a rock
Young sporophytes of the common moss Tortula muralis (wall screw-moss)
A small clump of moss.
Mosses are found chiefly in areas of dampness and low light. Mosses are common in wooded areas and at the edges of streams. Mosses are also found in cracks between paving stones in damp city streets. Some types have adapted to urban conditions and are found only in cities. A few species are wholly aquatic, such as Fontinalis antipyretica, and others such as Sphagnum inhabit bogs, marshes and very slow-moving waterways. Such aquatic or semi-aquatic mosses can greatly exceed the normal range of lengths seen in terrestrial mosses. Individual plants 20–30 cm (8-12 in) or more long are common in Sphagnum species for example.
Wherever they occur, mosses require moisture to survive because of the small size and thinness of tissues, lack of cuticle (waxy covering to prevent water loss), and the need for liquid water to complete fertilisation. Some mosses can survive desiccation, returning to life within a few hours of rehydration.
In northern latitudes, the north side of trees and rocks will generally have more moss on average than other sides (though south-side outcroppings are not unknown). This is assumed to be because of the lack of sufficient water for reproduction on the sun-facing side of trees. South of the equator the reverse is true. In deep forests where sunlight does not penetrate, mosses grow equally well on all sides of the tree trunk.[citation needed]
Cultivation
Moss is considered a weed in grass lawns, but is deliberately encouraged to grow under aesthetic principles exemplified by Japanese gardening. In old temple gardens, moss can carpet a forest scene. Moss is thought to add a sense of calm, age, and stillness to a garden scene. Rules of cultivation are not widely established. Moss collections are quite often begun using samples transplanted from the wild in a water-retaining bag. However, specific species of moss can be extremely difficult to maintain away from their natural sites with their unique combinations of light, humidity, shelter from wind, etc.
Growing moss from spores is even less controlled. Moss spores fall in a constant rain on exposed surfaces; those surfaces which are hospitable to a certain species of moss will typically be colonised by that moss within a few years of exposure to wind and rain. Materials which are porous and moisture retentive, such as brick, wood, and certain coarse concrete mixtures are hospitable to moss. Surfaces can also be prepared with acidic substances, including buttermilk, yogurt, urine, and gently puréed mixtures of moss samples, water and ericaceous compost.
Inhibiting moss growth
Moss growth can be inhibited by a number of methods:
Decreasing availability of water through drainage or direct application changes.
Increasing direct sunlight.
Increasing number and resources available for competitive plants like grasses.
Increasing the soil pH with the application of lime.
Heavy traffic or manually disturbing the moss bed with a rake will also inhibit moss growth.
The application of products containing ferrous sulfate or ferrous ammonium sulfate will kill moss, these ingredients are typically in commercial moss control products and fertilizers. Sulfur and Iron are essential nutrients for some competing plants like grasses. Killing moss will not prevent regrowth unless conditions favorable to their growth are changed.[6]
Mossery
A passing fad for moss-collecting in the late 19th century led to the establishment of mosseries in many British and American gardens. The mossery is typically constructed out of slatted wood, with a flat roof, open to the north side (maintaining shade). Samples of moss were installed in the cracks between wood slats. The whole mossery would then be regularly moistened to maintain growth.
Commercial use
There is a substantial market in mosses gathered from the wild. The uses for intact moss are principally in the florist trade and for home decoration. Decaying moss in the genus Sphagnum is also the major component of peat, which is "mined" for use as a fuel, as a horticultural soil additive, and in smoking malt in the production of Scotch whisky.
Sphagnum moss, generally the species cristatum and subnitens, is harvested while still growing and is dried out to be used in nurseries and horticulture as a plant growing medium. The practice of harvesting peat moss should not be confused with the harvesting of moss peat.
Peat moss can be harvested on a sustainable basis and managed so that regrowth is allowed, whereas the harvesting of moss peat is generally considered to cause significant environmental damage as the peat is stripped with little or no chance of recovery.
In World War II, Sphagnum mosses were used as first-aid dressings on soldiers' wounds, as these mosses are highly absorbent and have mild antibacterial properties. Some early people used it as a diaper due to its high absorbency.[citation needed]
In rural UK, Fontinalis antipyretica was traditionally used to extinguish fires as it could be found in substantial quantities in slow-moving rivers and the moss retained large volumes of water which helped extinguish the flames. This historical use is reflected in its specific Latin/Greek name, the approximate meaning of which is "against fire".
In Finland, peat mosses have been used to make bread during famines.[citation needed]
In Mexico, Moss is used as a Christmas decoration.
Moss photobioreactor with Physcomitrella patens
Physcomitrella patens is increasingly used in biotechnology. Prominent examples are the identification of moss genes with implications for crop improvement or human health [7] and the safe production of complex biopharmaceuticals in the moss bioreactor, developed by Ralf Reski and his co-workers [8].
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