Nerve - wikipedia Nerve This article is about neural pathways of the peripheral nervous system. For other uses, see Nerve ( disambiguation ). Nerve Nerves ( yellow ) in the arm Details Identifiers Latin nervus TA A14. 2.00. 013 FMA 65239 65132, 65239 Anatomical terminology ( edit on Wikidata ) A nerve is an enclosed, cable - like bundle of axons ( nerve fibers, the long and slender projections of neurons ) in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons to peripheral organs. In the central nervous system, the analogous structures are known as tracts. Neurons are sometimes called nerve cells, though this term is potentially misleading since many neurons do not form nerves, and nerves also include non-neuronal Schwann cells that coat the axons in myelin. Each nerve is a cordlike structure containing bundles of axons. 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. Contents 1 Anatomy 2 Physiology 3 Clinical significance 4 Growth and stimulation 5 Regeneration of peripheral nerve fibers 6 Other animals 7 See also 8 References 9 Further reading 10 External links Anatomy Nerves are categorized into three groups based on the direction that signals are conducted : Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the 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. 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 nerves innervate parts of the head, and connect directly to the brain ( especially to the brainstem ). They are typically assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included. In addition, cranial nerves have descriptive names. Cross-section of a nerve Each nerve is covered externally by a dense sheath of connective tissue, the epineurium. Underlying this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Nerves are bundled along with blood vessels, since the neurons of a nerve have fairly high energy requirements. 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. 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. Physiology A nerve conveys information in the form of electrochemical impulses ( as nerve impulses known as action potentials ) carried by the individual neurons that make up the nerve. These impulses are extremely fast, with some myelinated neurons conducting at speeds up to 120 m / s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and then back to electrical. 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. 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. Clinical significance Micrograph demonstrating perineural invasion of prostate cancer. H&E stain. Cancer can spread by invading the spaces around nerves. This is particularly common in head and neck cancer, and prostate and colorectal cancer. Nerves can be damaged by physical injury as well conditions like carpal tunnel syndrome 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 pinched nerve occurs when pressure is placed on a nerve, usually from swelling due to an injury, or pregnancy and can result in pain, weakness, numbness or paralysis. Symptoms may be felt in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain can happen when the damage causes altered signalling to other areas. 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, electromyography ( EMG ), and computed tomography ( CT ). Growth and stimulation Nerve growth normally ends in adolescence, but can be re-stimulated with a molecular mechanism known as `` Notch signaling. '' Regeneration of peripheral nerve fibers It has also been discovered through research that if the axons of a neuron were damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells. This is also referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, and the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud. When one of the growth processes finds the regeneration tube, it begins to grow rapidly towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is very slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. 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. 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. In vertebrates, the best known identified neurons are the gigantic Mauthner cells of fish. 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. 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. In organisms of radial symmetry nerve nets serve for the nervous system. There is no brain or centralised head region, and instead there are interconnected neurons spread out in nerve nets. These are found in Cnidaria, Ctenophora and Echinodermata. See also Connective tissue in the peripheral nervous system Dermatome ( anatomy ) List of nerves of the human body Nerve injury Nervous system Neuropathy Peripheral nerve injury Peripheral nerve injury classification References ^ Jump up to : Purves D, Augustine GJ, Fitzppatrick D, et al. ( 2008 ). Neuroscience ( 4th ed. ). Sinauer Associates. pp. 11 -- 20. ISBN 978 - 0 - 87893 - 697 - 7. ^ Jump up to : Marieb EN, Hoehn K ( 2007 ). Human Anatomy & Physiology ( 7th ed. ). Pearson. pp. 388 -- 602. ISBN 0 - 8053 - 5909 - 5. Jump up ^ Kanda, T ( Feb 2013 ). `` Biology of the blood - nerve barrier and its alteration in immune mediated neuropathies ''. Neurol Neurosurg Psychiatry. 84 ( 2 ) : 208 -- 212. doi : 10.1136 / jnnp - 2012 - 302312. PMID 23243216. Jump up ^ Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony - Samuel LaMantia, James O. McNamara, and Leonard E. White ( 2008 ). Neuroscience. 4th ed. Sinauer Associates. pp. 11 -- 20. ISBN 978 - 0 - 87893 - 697 - 7. CS1 maint : Multiple names : authors list ( link ) Jump up ^ Weinberg. Normal computed tomography of the brain. p. 109. Jump up ^ Yale Study Shows Way To Re-Stimulate Brain Cell Growth ScienceDaily ( Oct. 22, 1999 ) -- Results Could Boost Understanding Of Alzheimer 's, Other Brain Disorders Jump up ^ Kunik, D ( 2011 ). `` Laser - based single - axon transection for high - content axon injury and regeneration studies ''. PLoS ONE. 6 ( 11 ) : e26832. doi : 10.1371 / journal. pone. 0026832. PMC 3206876. PMID 22073205. Jump up ^ Burnett & Zager, Mark & Eric. `` Pathophysiology of Peripheral Nerve Injury : A Brief Review : Nerve Regeneration ''. Medscape Article. Medscape. Retrieved 2011 - 10 - 26. Jump up ^ Hoyle G, Wiersma CA ( 1977 ). Identified neurons and behavior of arthropods. Plenum Press. ISBN 978 - 0 - 306 - 31001 - 0. Jump up ^ `` Wormbook : Specification of the nervous system ''. Jump up ^ Stein PSG ( 1999 ). Neurons, Networks, and Motor Behavior. MIT Press. pp. 38 -- 44. ISBN 978 - 0 - 262 - 69227 - 4. Jump up ^ Stein, p. 112 Jump up ^ Simmons PJ, Young D ( 1999 ). Nerve cells and animal behaviour. Cambridge University Press. p. 43. ISBN 978 - 0 - 521 - 62726 - 9. 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. Kandel, ER ; Schwartz JH ; Jessell TM ( 2012 ). Principles of Neural Science ( 5th ed. ). New York : McGraw - Hill. ISBN 0 - 8385 - 7701 - 6. Squire, L. et al. ( 2012 ). Fundamental Neuroscience, 4th edition. Academic Press ; ISBN 0 - 12 - 660303 - 0 Andreasen, Nancy C. ( March 4, 2004 ). Brave New Brain : Conquering Mental Illness in the Era of the Genome. Oxford University Press. ISBN 978 - 0 - 19 - 514509 - 0. Archived from the original on February 24, 2007. Damasio, A.R. ( 1994 ). Descartes ' Error : Emotion, Reason, and the Human Brain. New York, Avon Books. ISBN 0 - 399 - 13894 - 3 ( Hardcover ) ISBN 0 - 380 - 72647 - 5 ( Paperback ) Gardner, H. ( 1976 ). The Shattered Mind : The Person After Brain Damage. New York, Vintage Books, 1976 ISBN 0 - 394 - 71946 - 8 Goldstein, K. ( 2000 ). The Organism. New York, Zone Books. ISBN 0 - 942299 - 96 - 5 ( Hardcover ) 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 0 - 262 - 12310 - X. External links Wikimedia Commons has media related to Nerves. Library resources about Nerve Resources in your library List of nerves The Nervous System at Wikibooks ( human ) Nervous System at Wikibooks ( non-human ) Human systems and organs Musculoskeletal Skeletal system Bone Carpus Collar bone ( clavicle ) Thigh bone ( femur ) Fibula Humerus Mandible Metacarpus Metatarsus Ossicles Patella Phalanges Radius Skull Tarsus Tibia Ulna Rib Vertebra Pelvis Sternum Cartilage Joints Fibrous joint Cartilaginous joint Synovial joint Muscular system Muscle Tendon Diaphragm Circulatory system Cardiovascular system peripheral Artery Vein Lymphatic vessel Heart Lymphatic system primary Bone marrow Thymus secondary Spleen Lymph node CNS equivalent Glymphatic system Nervous system Brain Spinal cord Nerve Sensory system Ear Eye Integumentary system Skin Subcutaneous tissue Breast Mammary gland Immune system Myeloid Myeloid immune system Lymphoid Lymphoid immune system Respiratory system Upper Nose Nasopharynx Larynx Lower Trachea Bronchus Lung Digestive system Mouth Salivary gland Tongue upper GI Oropharynx Laryngopharynx Esophagus Stomach lower GI Small intestine Appendix Colon Rectum Anus accessory Liver Biliary tract Pancreas Urinary system Genitourinary system Kidney Ureter Bladder Urethra Reproductive system Female Uterus Vagina Vulva Ovary Placenta Male Scrotum Penis Prostate Testicle Seminal vesicle Endocrine system Pituitary Pineal Thyroid Parathyroid Adrenal Islets of Langerhans Spinal nerves Cervical C1 C2 C3 C4 C5 C6 C7 C8 anterior Cervical plexus Brachial plexus posterior Posterior branches of cervical nerves Suboccipital -- C1 Greater occipital -- C2 Third occipital -- C3 Thoracic T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 anterior Intercostal Intercostobrachial -- T2 Thoraco - abdominal nerves -- T7 -- T11 Subcostal -- T12 posterior Posterior branches of thoracic nerves Lumbar L1 L2 L3 L4 L5 anterior Lumbar plexus Lumbosacral trunk posterior Posterior branches of the lumbar nerves Superior cluneal L1 -- L3 Sacral S1 S2 S3 S4 S5 anterior Sacral plexus posterior Posterior branches of sacral nerves Medial cluneal nerves Coccygeal anterior Coccygeal plexus posterior Posterior branch of coccygeal nerve The cranial nerves terminal Nuclei Septal nuclei Course no significant branches olfactory Nuclei Anterior olfactory nucleus Course olfactory bulb olfactory tract optic Nuclei Lateral geniculate nucleus Course optic chiasm optic tract oculomotor Nuclei Oculomotor nucleus Edinger -- Westphal nucleus Branches superior parasympathetic root of ciliary ganglion / ciliary ganglion inferior trochlear Nucleus Branches no significant branches trigeminal Nuclei PSN Spinal trigeminal nucleus MN TMN Course trigeminal ganglion Branches ophthalmic maxillary mandibular abducens Nucleus Branches no significant branches facial near origin intermediate nerve geniculate inside facial canal greater petrosal pterygopalatine ganglion nerve to the stapedius chorda tympani lingual nerve submandibular ganglion at stylomastoid foramen posterior auricular suprahyoid digastric stylohyoid parotid plexus temporal zygomatic buccal mandibular cervical Nuclei Facial motor nucleus Solitary nucleus Superior salivary nucleus vestibulocochlear Nuclei Vestibular nuclei Cochlear nuclei cochlear nerve striae medullares lateral lemniscus vestibular Scarpa 's ganglion glossopharyngeal before jugular fossa ganglia superior inferior after jugular fossa tympanic tympanic plexus lesser petrosal otic ganglion stylopharyngeal branch pharyngeal branches tonsillar branches lingual branches carotid sinus Nuclei Nucleus ambiguus Inferior salivatory nucleus Solitary nucleus vagus before jugular fossa ganglia superior inferior after jugular fossa meningeal branch auricular branch neck pharyngeal branch pharyngeal plexus superior laryngeal external internal recurrent laryngeal ( inferior ) superior cervical cardiac thorax inferior cardiac pulmonary vagal trunks anterior posterior abdomen celiac renal hepatic anterior gastric posterior gastric Nuclei Nucleus ambiguus Dorsal nucleus of vagus nerve Solitary nucleus accessory Nuclei Nucleus ambiguus Spinal accessory nucleus cranial spinal hypoglossal Nucleus Branches lingual Nerves of the cervical plexus Superficial C2 Lesser occipital C2 -- C3 Greater auricular Transverse cervical C3 -- C4 Supraclavicular Deep C1 -- C3 Ansa cervicalis superior root inferior root C3 -- C5 Phrenic Nerves of the brachial plexus Supraclavicular root ( dorsal scapular, long thoracic ) upper trunk ( suprascapular, to the subclavius ) Infraclavicular lateral cord lateral pectoral ansa pectoralis musculocutaneous ( lateral cutaneous of forearm ) median / lateral root : anterior interosseous palmar recurrent common palmar digital ( proper palmar digital ) medial cord medial pectoral ansa pectoralis cutaneous : medial cutaneous of forearm medial cutaneous of arm ulnar : muscular palmar dorsal ( dorsal digital nerves ) superficial ( common palmar digital, proper palmar digital ) deep median / medial root : see above posterior cord subscapular ( upper, lower ) thoracodorsal axillary ( superior lateral cutaneous of arm ) radial : muscular cutaneous ( posterior of arm, inferior lateral of arm, posterior of forearm ) superficial ( dorsal digital nerves ) deep ( posterior interosseous ) Other cutaneous innervation of the upper limbs Anatomy of the autonomic nervous system Head Sympathetic Cervical Chain Ganglion : roots long ciliary Deep Petrosal Parasympathetic Ciliary ganglion : roots Sensory Parasympathetic Short ciliary Pterygopalatine ganglion : deep petrosal nerve of pterygoid canal branches of distribution : greater palatine inferior posterior nasal branches lesser palatine nasopalatine medial superior posterior nasal branches pharyngeal Submandibular ganglion Otic ganglion Neck Sympathetic paravertebral ganglia : Cervical ganglia Superior Middle Inferior Stellate ganglion prevertebral plexus : Cavernous plexus Internal carotid Chest Sympathetic paravertebral ganglia : Thoracic ganglia prevertebral plexus : Cardiac plexus Esophageal plexus Pulmonary plexus Thoracic aortic plexus splanchnic nerves : cardiopulmonary thoracic cardiac nerves : Superior Middle Inferior Abdomen Sympathetic paravertebral ganglia : Lumbar ganglia prevertebral ganglia : Celiac ganglia Aorticorenal Superior mesenteric ganglion Inferior mesenteric ganglion prevertebral plexus : Celiac plexus Hepatic Splenic Pancreatic aorticorenal Abdominal aortic plexus Renal / Suprarenal Superior mesenteric Gastric Inferior mesenteric Spermatic Ovarian Superior hypogastric hypogastric nerve Superior rectal Inferior hypogastric Vesical Prostatic / Cavernous nerves of penis Uterovaginal Middle rectal splanchnic nerves : Lumbar splanchnic nerves Enteric Submucous plexus Myenteric plexus Pelvis Sympathetic paravertebral ganglia : Sacral ganglia Ganglion impar splanchnic nerves : Sacral splanchnic nerves Parasympathetic splanchnic nerves : Pelvic splanchnic nerves Nerves of the lumbosacral plexus Lumbar plexus iliohypogastric lateral cutaneous branch anterior cutaneous branch ilioinguinal anterior scrotal ♂ / labial ♀ genitofemoral femoral branch genital branch Lateral cutaneous patellar obturator anterior cutaneous posterior accessory femoral anterior cutaneous branches saphenous ( infrapatellar medial crural cutaneous sacral plexus sciatic common peroneal lateral sural cutaneous communicating branch deep peroneal lateral terminal branch medial terminal branch dorsal digital superficial peroneal medial dorsal cutaneous intermediate dorsal cutaneous dorsal digital tibial medial sural cutaneous medial calcaneal medial plantar ( common plantar digital nerves proper plantar digital ) lateral plantar ( deep branch superficial branch common plantar digital proper plantar digital ) sural lateral dorsal cutaneous lateral calcaneal other Muscular superior gluteal inferior gluteal lateral rotator group ( to quadratus femoris to obturator internus to the piriformis ) cutaneous : posterior cutaneous of thigh ( inferior cluneal perineal branches ) perforating cutaneous coccygeal plexus pudendal inferior anal perineal deep posterior scrotal ♂ / labial ♀ dorsal of the penis ♂ / clitoris ♀ anococcygeal Related cutaneous innervation of the lower limbs NDL : 00571039 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Nerve&oldid=812400470 '' Categories : Nerves Peripheral nervous system Neuroanatomy Soft tissue Hidden categories : CS1 maint : Multiple names : authors list Talk Contents About Wikipedia Afrikaans Alemannisch Aragonés ܐܪܡܝܐ Asturianu Авар Azərbaycanca বাংলা Bân - lâm - gú Башҡортса Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Català Čeština ChiShona Cymraeg Dansk Deutsch ދިވެހިބަސް Eesti Ελληνικά Español Esperanto فارسی Français Gaelg Gàidhlig Galego 한국어 Հայերեն हिन्दी Ido Bahasa Indonesia Íslenska Italiano עברית ქართული Қазақша Kiswahili Kurdî Кыргызча Лакку Latina Latviešu Lietuvių Lumbaart Македонски മലയാളം Bahasa Melayu မြန်မာဘာသာ 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Question: fascicles within spinal nerves are surrounded by fibers of the
Answer: perineurium