Nerve
Nerve | |
---|---|
Details | |
System | Nervous system |
Identifiers | |
Latin | nervus |
TA98 | A14.2.00.013 |
TA2 | 6154 |
FMA | 65132 |
Anatomical terms of neuroanatomy |
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon, within the nerve, is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium. Nerve cells (often called neurons) are further classified as sensory, motor, or mixed nerves.
In the central nervous system, the analogous structures are known as nerve tracts.[1][2]
Structure
Each nerve is covered on the outside by a dense sheath of
Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood–brain barrier.[3] Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.
Categories
Nerves are categorized into three groups based on the direction that signals are conducted:
- mechanoreceptors in skin.
- Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands.
- Mixed nerves contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. All spinal nerves are mixed nerves, and some of the cranial nerves are also mixed nerves.
Nerves can be categorized into two groups based on where they connect to the central nervous system:
- Spinal nerves innervate (distribute to/stimulate) much of the body, and connect through the vertebral column to the spinal cord and thus to the central nervous system. They are given letter-number designations according to the vertebra through which they connect to the spinal column.
- cranial nerve zerois sometimes included. In addition, cranial nerves have descriptive names.
Terminology
Specific terms are used to describe nerves and their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to innervate that section of the body or organ. Other terms relate to whether the nerve affects the same side ("ipsilateral") or opposite side ("contralateral") of the body, to the part of the brain that supplies it.
Development
Nerve growth normally ends in adolescence, but can be re-stimulated with a molecular mechanism known as "
Regeneration
If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons can regenerate and remake the synaptic connections with neurons with the help of guidepost cells. This is also referred to as neuroregeneration.[5]
The nerve begins the process by destroying the nerve
Function
A nerve conveys information in the form of electrochemical impulses (as nerve impulses known as
Nerves can be categorized into two groups based on function:
- An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is then processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, and bundles of afferent fibers are known as sensory nerves.[1][2]
- An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves.
Nervous system
The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body.[7] In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain, brainstem and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to all remaining body parts.
Nerves that transmit signals from the CNS are called
The autonomic nervous system is further subdivided into the
Clinical significance
Cancer can spread by invading the spaces around nerves. This is particularly common in head and neck cancer, prostate cancer and colorectal cancer.
Nerves can be damaged by physical injury as well as conditions like carpal tunnel syndrome (CTS) and repetitive strain injury. Autoimmune diseases such as Guillain–Barré syndrome, neurodegenerative diseases, polyneuropathy, infection, neuritis, diabetes, or failure of the blood vessels surrounding the nerve all cause nerve damage, which can vary in severity.
Multiple sclerosis is a disease associated with extensive nerve damage. It occurs when the macrophages of an individual's own immune system damage the myelin sheaths that insulate the axon of the nerve.
A
Other animals
A neuron is called identified if it has properties that distinguish it from every other neuron in the same animal—properties such as location, neurotransmitter, gene expression pattern, and connectivity—and if every individual organism belonging to the same species has exactly one neuron with the same set of properties.[9] In vertebrate nervous systems, very few neurons are "identified" in this sense. Researchers believe humans have none—but in simpler nervous systems, some or all neurons may be thus unique.[10]
In vertebrates, the best known identified neurons are the gigantic Mauthner cells of fish.[11]: 38–44 Every fish has two Mauthner cells, located in the bottom part of the brainstem, one on the left side and one on the right. Each Mauthner cell has an axon that crosses over, innervating (stimulating) neurons at the same brain level and then travelling down through the spinal cord, making numerous connections as it goes. The synapses generated by a Mauthner cell are so powerful that a single action potential gives rise to a major behavioral response: within milliseconds the fish curves its body into a C-shape, then straightens, thereby propelling itself rapidly forward. Functionally this is a fast escape response, triggered most easily by a strong sound wave or pressure wave impinging on the lateral line organ of the fish. Mauthner cells are not the only identified neurons in fish—there are about 20 more types, including pairs of "Mauthner cell analogs" in each spinal segmental nucleus. Although a Mauthner cell is capable of bringing about an escape response all by itself, in the context of ordinary behavior other types of cells usually contribute to shaping the amplitude and direction of the response.
Mauthner cells have been described as command neurons. A command neuron is a special type of identified neuron, defined as a neuron that is capable of driving a specific behavior all by itself.[11]: 112 Such neurons appear most commonly in the fast escape systems of various species—the squid giant axon and squid giant synapse, used for pioneering experiments in neurophysiology because of their enormous size, both participate in the fast escape circuit of the squid. The concept of a command neuron has, however, become controversial, because of studies showing that some neurons that initially appeared to fit the description were really only capable of evoking a response in a limited set of circumstances.[12]
In organisms of
History
Modern research has not confirmed
See also
- Connective tissue in the peripheral nervous system
- Dermatome (anatomy)
- List of nerves of the human body
- Nerve injury
- Neuropathy
- Nerve injury classification
References
- ^ ISBN 978-0-87893-697-7.
- ^ ISBN 978-0-8053-5909-1.
- S2CID 207005110.
- ^ Yale Study Shows Way To Re-Stimulate Brain Cell Growth ScienceDaily Archived 2017-07-07 at the Wayback Machine (Oct. 22, 1999) — Results Could Boost Understanding Of Alzheimer's, Other Brain Disorders
- PMID 22073205.
- ^ Burnett, Mark; Zager, Eric. "Pathophysiology of Peripheral Nerve Injury: A Brief Review: Nerve Regeneration". Medscape Article. Medscape. Archived from the original on 2011-10-31. Retrieved 2011-10-26.
- ISBN 978-1-119-34373-8.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ Weinberg. Normal computed tomography of the brain. p. 109.[full citation needed]
- ISBN 978-0-306-31001-0.
- ^ "Wormbook: Specification of the nervous system". Archived from the original on 2011-07-17.
- ^ ISBN 978-0-262-69227-4.
- ISBN 978-0-521-62726-9.
- ^
Pickering, Neil (2006). The Metaphor of Mental Illness. International perspectives in philosophy and psychiatry. Oxford University Press. p. 99. ISBN 9780198530879. Retrieved 27 May 2023.
[...] William Cullen [...] as early as 1785 [...] postulated that certain mental disorders were the result of some unknown physical change in the nerves, for which he coined the term neurosis. This term has since quite altered its meaning, as it now refers not to a state of the nerves but to a nervous state.
- ^
For example:
ISBN 9780674049161. Retrieved 27 May 2023.
'Mr. Bennet, how can you abuse your own children in such a way? You take delight in vexing me. You have no compassion on my poor nerves.' [...] 'You mistake me, my dear. I have a high respect for your nerves. They are my old friends. I have heard you mention them with consideration these twenty years at least.'
- ^
Pickering, Neil (2006). The Metaphor of Mental Illness. International perspectives in philosophy and psychiatry. Oxford University Press. p. 1. ISBN 9780198530879. Retrieved 27 May 2023.
[...] in everyday English we find [...] lay terms such as 'nervous breakdown' that relate to mental illness as a whole [...]
Further reading
- Nervous system William E. Skaggs, Scholarpedia
- Bear, M. F.; B. W. Connors; M. A. Paradiso (2006). Neuroscience: Exploring the Brain (3rd ed.). Philadelphia: Lippincott. ISBN 0-7817-6003-8.
- Binder, Marc D.; Hirokawa, Nobutaka; Windhorst, Uwe, eds. (2009). Encyclopedia of Neuroscience. Springer. ISBN 978-3-540-23735-8.
- ISBN 978-0-8385-7701-1.
- Squire, L. et al. (2012). Fundamental Neuroscience, 4th edition. ISBN 0-12-660303-0
- ISBN 978-0-19-514509-0.
- Damasio, A. R. (1994). Descartes' Error: Emotion, Reason, and the Human Brain. New York, ISBN 0-380-72647-5(Paperback)
- Gardner, H. (1976). The Shattered Mind: The Person After Brain Damage. New York, ISBN 0-394-71946-8
- Goldstein, K. (2000). The Organism. New York, Zone Books. ISBN 0-942299-97-3(Paperback)
- Lauwereyns, Jan (February 2010). The Anatomy of Bias: How Neural Circuits Weigh the Options. Cambridge, Massachusetts: The MIT Press. ISBN 978-0-262-12310-5.
External links
- List of nerves
- The Nervous System at Wikibooks (human)
- Nervous System at Wikibooks (non-human)
- Parsons, Frederick Gymer (1911). Encyclopædia Britannica. Vol. 19 (11th ed.). pp. 394–400. .