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Encyclopedia > Nerve
Nerves (yellow)

A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the non-axon glial cells that ensheath the axons in myelin. Nerve may refer to more than one thing: Nerves are part of the nervous system. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links Download high resolution version (524x1000, 111 KB) Beskrivelse from Grays Anatomy of the Human body, 1918, Copyright expired Licensing File links The following pages link to this file: Median nerve ... Image File history File links Download high resolution version (524x1000, 111 KB) Beskrivelse from Grays Anatomy of the Human body, 1918, Copyright expired Licensing File links The following pages link to this file: Median nerve ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... This article is about cells in the nervous system. ... Neuroglia cells of the brain shown by Golgis method. ... Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ...

Contents

Anatomy

Nerves are part of the peripheral nervous system. Afferent nerves convey sensory signals to the central nervous system, 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 axons are often arranged together, forming mixed nerves. For example, the median nerve controls motor and sensory function in the hand. The Peripheral nervous system resides or extends outside the CNS central nervous system (the brain and spinal cord) to serve the limbs and organs. ... The mechanism of the reflex arc In the nervous system, afferent neurons--otherwise known as sensory or receptor neurons--carry nerve impulses from receptors or sense organs toward the central nervous system. ... This article is about the senses of living organisms (vision, taste, etc. ... A diagram showing the CNS: 1. ... In the nervous system, efferent nerves otherwise known as motor or effector neuron carry nerve impulses away from the central nervous systemto effectors - either muscles or glands. ... For other uses of Muscles, see Muscles (disambiguation). ... Human submaxillary gland. ...


Billions of long nerve cells, called neurons, make up the body's nervous system. Neurons receive and transmit chemical-electrical messages to and from the brain. Each neuron is long and thin. One end receives messages and the other transmits the message to the next neuron. The messages "jump" across a gap from one neuron cell to another.


Each peripheral nerve is covered externally by a dense sheath of connective tissue, the epineurium. Underlying this is a layer of flat cells forming a complete sleeve, the perineurium. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurial sheath. This forms an unbroken tube which extends from the surface of the spinal cord to the level at which the axon synapses with its muscle fibres or ends in sensory receptors. The endoneurial sheath consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Peripheral nerves are richly supplied with blood. Neurolemma (spelled also neurolema, neurilemma and neurilema, and used interchangeably with epineurium) is the insulating myelin layer that surrounds an individual peripheral nerve fiber. ... In a nerve fiber, the tubular sheath of the funiculi, perineurium, is a fine, smooth, transparent membrane, which may be easily separated, in the form of a tube, from the fibers it encloses; in structure it is made up of connective tissue, which has a distinctly lamellar arrangement. ... The nerve fibers are held together and supported within the funiculus by delicate connective tissue, called the endoneurium. ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... It has been suggested that this article or section be merged with Glycocalix. ...


Most nerves connect to the central nervous system through the spinal cord. The twelve cranial nerves, however, connect directly to parts of the brain. 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 major nerves have descriptive names. Inside the central nervous system, distinguishable bundles of axons are termed tracts rather than nerves. A diagram showing the CNS: 1. ... The Spinal cord nested in the vertebral column. ... Cranial nerves Cranial nerves are nerves that emerge directly from the brain in contrast to spinal nerves which emerge from segments of the spinal cord. ... Human brain In animals, the brain (enkephale) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. ... A diagram of a thoracic vertebra. ... Roman numerals are a numeral system originating in ancient Rome, adapted from Etruscan numerals. ...


The signals that nerves carry, sometimes called nerve impulses, are also known as action potentials. These are rapidly (up to 120 m/s) traveling electrical waves, which typically begin in the cell body of a neuron and propagate down the axon to its tip or "terminus." The signals cross over from the terminus of the axon to the adjacent neurotransmitter receptor through a gap called the synapse. Motor neurons innervate or activate muscles groups. A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Illustration of the major elements in a prototypical synapse. ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ...


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. A pinched nerve occurs 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, signalling is defective from all parts of the area from 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). This article is about the medical condition. ... Guillain-Barré syndrome (GBS) (IPA pronunciation: is an acute, autoimmune, polyradiculoneuropathy affecting the peripheral nervous system, usually triggered by an acute infectious process. ... Inflammation is the first response of the immune system to infection or irritation and may be referred to as the innate cascade. ... This article is about the disease that features high blood sugar. ... Look up Pain in Wiktionary, the free dictionary. ... Paralysed redirects here. ... This article does not cite any references or sources. ... Neurology is a branch of medicine dealing with disorders of the nervous system. ... In medicine, the physical examination or clinical examination is the process by which the physician investigates the body of a patient for signs of disease. ... For other uses, see Reflexive (disambiguation). ... This article does not cite any references or sources. ... For other uses of Muscles, see Muscles (disambiguation). ... // Proprioception (PRO-pree-o-SEP-shun (IPA pronunciation: ); from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ... Somatic sensation consists of the various sensory receptors that trigger the experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), and the sensations of muscle movement and joint position including posture, movement, and facial expression (collectively also called proprioception). ... A nerve conduction study (NCS) is a test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. ... Electromyography (EMG) is a technique for evaluating and recording physiologic properties of muscles at rest and while contracting. ...


See also

The nervous system is a highly specialized network whose principal components are nerves called neurons. ... There is no single classification system that can describe all the many variations of nerve injury. ...

Additional images

The sural nerve (short saphenous nerve), formed by the junction of the medial sural cutaneous with the peroneal anastomotic branch, passes downward near the lateral margin of the tendo calcaneus, lying close to the small saphenous vein, to the interval between the lateral malleolus and the calcaneus. ... The superior gluteal nerve is a nerve that originates in the pelvis which supplies the gluteus medius, the gluteus minimus, and the tensor fasciae latae muscles. ... The Superior Gluteal Nerve () arises from the dorsal divisions of the fourth and fifth lumbar and first sacral nerves: it leaves the pelvis through the greater sciatic foramen above the Piriformis, accompanied by the superior gluteal vessels, and divides into a superior and an inferior branch. ... The Lateral rotator group are a group of muscles of the hip consisting of the externus obturator, the internus obturator, the piriformis, the superior gemellus, the inferior gemellus, and the quadratus femoris. ... The nerve to quadratus femoris is a nerve that provides innervation to the quadratus femoris and gemellus inferior muscles. ... The nerve to obturator internus is a nerve that innervates the obturator internus and gemellus superior muscles. ... The nerve to piriformis is a nerve that innervates the piriformis muscle. ... The posterior cutaneous nerve of the thigh (also called the posterior femoral cutaneous nerve) provides innervation to the skin of the posterior surface of the thigh and leg, as well as to the skin of the perineum. ... The inferior clunial nerves innervate the skin of the lower part of the buttocks. ... The perineal branches of the posterior femoral cutaneous nerve are distributed to the skin at the upper and medial side of the thigh. ... The Perforating Cutaneous Nerve usually arises from the posterior surface of the second and third sacral nerves. ... The coccygeal plexus is a plexus of nerves near the coccyx bone. ... The pudendal nerve is responsible for orgasm, urination, and defecation in both sexes. ... The Inferior rectal nerves (inferior anal nerves, inferior hemorrhoidal nerve) occasionally arises directly from the sacral plexus; it crosses the ischiorectal fossa, with the inferior hemorrhoidal vessels, toward the anal canal and the lower end of the rectum, and is distributed to the Sphincter ani externus and to the integument... The perineal nerve is a nerve arising from the pudendal nerve that supplies the perineum. ... The posterior scrotal (or labial) branches; superficial peroneal nerves) are two in number, medial and lateral. ... The dorsal nerve of the penis is the deepest division of the pudendal nerve; it accompanies the internal pudendal artery along the ramus of the ischium; it then runs forward along the margin of the inferior ramus of the pubis, between the superior and inferior layers of the fascia of... The dorsal nerve of the clitoris is a nerve in females that branches off the pudendal nerve to innervate the clitoris. ... Anococcygeal Nerves: The fifth sacral nerve receives a communicating filament from the fourth, and unites with the coccygeal nerve to form the coccygeal plexus. ... Foot. ...

  Results from FactBites:
 
Nerve - Wikipedia, the free encyclopedia (288 words)
A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin.
These signals, sometimes called nerve impulses, are also known as action potentials: rapidly traveling electrical waves, which begin typically 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.
Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis.
  More results at FactBites »

 
 

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