Difference between revisions of "Nerve" - New World Encyclopedia
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| − | [[Image:Gray816.png|thumb|250px| | + | [[Image:Gray816.png|thumb|250px|In the anatomical drawing above, nerve fibers are highlighted in yellow.]] |
| − | A '''nerve''' is an enclosed, cable-like bundle of [[axon]]s (the long, slender projection of a neuron) | + | A '''nerve''' is an enclosed, cable-like bundle of [[axon]]s (the long, slender projection of a neuron) (what is the nerve enclosed by?). second sentence should be about the nervous system - signaling network of interconnected nerves. |
| − | + | [[Neuron]]s are sometimes called '''nerve cells''', though this term is technically imprecise since many neurons do not form nerves, and nerves also include the [[glial cells]] that form a [[myelin]] sheath around the axons. | |
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| − | + | Nerves are part of the [[peripheral nervous system]] of vertebrates? animals? (in contrast to CNS - brain and spinal cord; explain – actually, in intro, situate w/in nervous system). [[Afferent nerve]]s convey [[sense|sensory]] signals ''to'' the [[central nervous system]] (explain), for example from skin or organs, while [[efferent nerve]]s conduct stimulatory signals ''from'' the central nervous system to the [[muscle]]s and [[gland]]s. Afferent and efferent nerves are often arranged together, forming mixed nerves (or, it’s more that aff and eff neurons are together in a single nerve?). | |
| − | + | ==The components of nerves== | |
| + | neurons | ||
| + | schwann cells (explain why myelination [sp?] important) | ||
| + | connective tissue (made of interneurons? or schwann cells?) | ||
| + | peripheral nerves are richly supplied with blood. - are blood vessels considered part of a nerve? | ||
| − | The signals that nerves carry, sometimes called nerve impulses, are also known as [[action potential]]s: rapidly (up to 120 m/s) traveling electrical waves, which begin | + | ==Situating nerves within the vertebrate anatomy== |
| + | [[Image:Peripheral nerve, cross section.jpg|thumb|150px|left|Cross section of a peripheral nerve.]] | ||
| + | Each peripheral nerve is covered externally by a dense sheath of connective tissue called the epineurium. Underlying this is a layer of flat cells forming a complete sleeve, the perineurium. Perineurial septa extend into the nerve and subdivide it into several bundles of fibers. Surrounding each such fiber is the endoneurial sheath. This is a tube which extends, unbroken, from the surface of the spinal cord to the level at which the axon synapses with its muscle fibers or ends in sensory endings. The endoneurial sheath consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibers. | ||
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| + | Most nerves connect to the [[central nervous system]] through the [[spinal cord]]. The twelve [[cranial nerves]], however, connect directly to parts of the [[brain]]. | ||
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| + | Inside the central nervous system, bundles of axons are termed [[tract (anatomy)|tracts]] rather than nerves (why?). | ||
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| + | ==How nerves relay signals== | ||
| + | The signals that nerves carry, sometimes called nerve impulses, are also known as [[action potential]]s: rapidly (up to 120 m/s) traveling electrical waves, which typically begin in the cell body of a neuron and propagate rapidly down the axon to its tip or "terminus." The signals cross over from the terminus to the adjacent neurotransmitter receptor through a gap called the [[synapse]]. | ||
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| + | [[Motor neurons]] '''innervate''' or activate muscles groups. | ||
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| + | The nerve system runs through the spinal cord. | ||
== Clinical importance == | == Clinical importance == | ||
| − | Damage to nerves can be caused by physical injury, swelling (e.g. [[carpal tunnel syndrome]]), autoimmune diseases (e.g. [[Guillain-Barré syndrome]]), infection ([[neuritis]]), [[diabetes]], or failure of the blood vessels surrounding the nerve. Pinched nerves occur when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by [[Pain and nociception|pain]], numbness, weakness, or [[paralysis]]. Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called '''referred pain'''. Referred pain occurs because when a nerve is damaged, signaling is defective from all parts of the area which the nerve receives input, not just the site of the damage. | + | weird/out of place? Damage to nerves can be caused by physical injury, swelling (e.g. [[carpal tunnel syndrome]]), autoimmune diseases (e.g. [[Guillain-Barré syndrome]]), infection ([[neuritis]]), [[diabetes]], or failure of the blood vessels surrounding the nerve. Pinched nerves occur when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by [[Pain and nociception|pain]], numbness, weakness, or [[paralysis]]. Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called '''referred pain'''. Referred pain occurs because when a nerve is damaged, signaling is defective from all parts of the area which the nerve receives input, not just the site of the damage. |
[[Neurology|Neurologists]] usually diagnose disorders of the nerves by a [[physical examination]], including the testing of [[reflex]]es, [[walking]] and other directed movements, [[muscle]] weakness, [[proprioception]], and the sense of [[Somatosensory system|touch]]. This initial exam can be followed with tests such as [[nerve conduction study]] and [[electromyography]] (EMG). | [[Neurology|Neurologists]] usually diagnose disorders of the nerves by a [[physical examination]], including the testing of [[reflex]]es, [[walking]] and other directed movements, [[muscle]] weakness, [[proprioception]], and the sense of [[Somatosensory system|touch]]. This initial exam can be followed with tests such as [[nerve conduction study]] and [[electromyography]] (EMG). | ||
| − | == | + | ==Nomenclature?== |
| − | + | [[Spinal nerve]]s are given letter-number combinations according to the [[vertebra]] through which they connect to the spinal column. Cranial nerves are assigned numbers, usually expressed as [[Roman numeral]]s from I to XII. In addition, most nerves and major branches of nerves have descriptive names. | |
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{{Nerves}} | {{Nerves}} | ||
{{credit|Nerve|136477866}} | {{credit|Nerve|136477866}} | ||
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 16:43, 15 July 2007
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Please help improve this article or section by expanding it. Further information might be found on the talk page or at requests for expansion. This article has been tagged since April 2007. |
A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron) (what is the nerve enclosed by?). second sentence should be about the nervous system - signaling network of interconnected nerves.
Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the glial cells that form a myelin sheath around the axons.
Nerves are part of the peripheral nervous system of vertebrates? animals? (in contrast to CNS - brain and spinal cord; explain – actually, in intro, situate w/in nervous system). Afferent nerves convey sensory signals to the central nervous system (explain), for example from skin or organs, while efferent nerves conduct stimulatory signals from the central nervous system to the muscles and glands. Afferent and efferent nerves are often arranged together, forming mixed nerves (or, it’s more that aff and eff neurons are together in a single nerve?).
The components of nerves
neurons schwann cells (explain why myelination [sp?] important) connective tissue (made of interneurons? or schwann cells?) peripheral nerves are richly supplied with blood. - are blood vessels considered part of a nerve?
Situating nerves within the vertebrate anatomy
Each peripheral nerve is covered externally by a dense sheath of connective tissue called the epineurium. Underlying this is a layer of flat cells forming a complete sleeve, the perineurium. Perineurial septa extend into the nerve and subdivide it into several bundles of fibers. Surrounding each such fiber is the endoneurial sheath. This is a tube which extends, unbroken, from the surface of the spinal cord to the level at which the axon synapses with its muscle fibers or ends in sensory endings. The endoneurial sheath consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibers.
Most nerves connect to the central nervous system through the spinal cord. The twelve cranial nerves, however, connect directly to parts of the brain.
Inside the central nervous system, bundles of axons are termed tracts rather than nerves (why?).
How nerves relay signals
The signals that nerves carry, sometimes called nerve impulses, are also known as action potentials: rapidly (up to 120 m/s) traveling electrical waves, which typically begin in the cell body of a neuron and propagate rapidly down the axon to its tip or "terminus." The signals cross over from the terminus to the adjacent neurotransmitter receptor through a gap called the synapse.
Motor neurons innervate or activate muscles groups.
The nerve system runs through the spinal cord.
Clinical importance
weird/out of place? Damage to nerves can be caused by physical injury, swelling (e.g. carpal tunnel syndrome), autoimmune diseases (e.g. Guillain-Barré syndrome), infection (neuritis), diabetes, or failure of the blood vessels surrounding the nerve. Pinched nerves occur when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis. Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain occurs because when a nerve is damaged, signaling is defective from all parts of the area which the nerve receives input, not just the site of the damage.
Neurologists usually diagnose disorders of the nerves by a physical examination, including the testing of reflexes, walking and other directed movements, muscle weakness, proprioception, and the sense of touch. This initial exam can be followed with tests such as nerve conduction study and electromyography (EMG).
Nomenclature?
Spinal nerves are given letter-number combinations according to the vertebra through which they connect to the spinal column. Cranial nerves are assigned numbers, usually expressed as Roman numerals from I to XII. In addition, most nerves and major branches of nerves have descriptive names.
Template:Nerves
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