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see nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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the cordlike association of nerve tissues that links the brain and nerve ganglia by innervation to the other organs and tissues of the body.

A nerve primarily consists of nerve fibers. In vertebrates many nerves converge to form a bundle that is surrounded by a connective tissue sheath, the perineurium; the thin interstitial layers of connective tissue that separate the individual fibers deep within the bundle constitute the endoneurium. Finally, the entire nerve trunk, comprising several bundles, is covered by an additional sheath, the epineurium.

Nerves can be sensory (also called afferent or centripetal) or motor (also called efferent or centrifugal). Some nerves, for example, those innervating the skeletal muscles, mainly include myelinated, or medullated, fibers; others, for example, the sympathetic nerves, largely consist of unmyelinated, or unmedullated, fibers.

In reptiles, birds, mammals, and man 12 pairs of cranial nerves branch from the brain: the olfactory (cranial nerve I), the optic (cranial nerve II), the oculomotor (cranial nerve III), the trochlear (cranial nerve IV), the trigeminal (cranial nerve V), the abducent (cranial nerve VI), the facial (cranial nerve VII), the acoustic (cranial nerve VIII), the glossopharyngeal (cranial nerve IX), the vagus (cranial nerve X), the accessory (cranial nerve XI), and the hypoglossal (cranial nerve XII). Only the first ten pairs are present in fish and amphibians.

In man there are 31 pairs of spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal. Each pair innervates the effectors and receptors of a certain part of the body. The spinal nerves branch from the spinal cord into two roots—the posterior, or sensory, and the anterior, or motor. Both roots then combine to form a common trunk that consists of both sensory and motor fibers.

Several adjacent nerves can be combined into nerve plexuses, where an exchange of fibers between different nerves can take place. Three large plexuses are distinguished: the cervical, the brachial, and the lumbosacral. Each nerve plexus is the origin of several pairs of nerves; for example, the sacral portion of the lumbosacral plexus gives rise to the sciatic nerves.

Nerves that originate in the ganglia, trunks, and plexuses of the autonomic nervous system constitute a specific group. The optic nerve is remarkable for its large number of fibers; there are more than 1 million in the human optic nerve. Usually, however, there are 103 -104 fibers in a nerve. In invertebrates certain nerves are known to consist of only a few fibers. The peripheral nervous system in animals and man consists of aggregations of nerves.



A bundle of nerve fibers or processes held together by connective tissue.


Any one of the ribs of a groined vault, but esp. a rib which forms one of the sides of a compartment of the groining.


1. any of the cordlike bundles of fibres that conduct sensory or motor impulses between the brain or spinal cord and another part of the body
2. a large vein in a leaf
3. any of the veins of an insect's wing
References in periodicals archive ?
United's start was so nervy that Smalling visibly called for calm and Mourinho flashed glares from the touchline.
And defending champion Froome said: "It was a nervy day in case the crosswinds kicked off.
Cardiff hit back four minutes from time when substitute Jones headed home a Joe Ralls cross to set up a nervy climax but Boro - beaten just once in 15 games - held on for the three points.
Stevenson reduced the deficit with six minutes remaining to ensure a nervy ending, but Danny Lennon's side held out.
Things did not go to plan for Murray at the start as he was twice broken to lose a nervy opening set, but he turned things around in the second and was rarely troubled in the decider to come through 4-6 6-1 6-4.
Lennon was pleased with the result, but the former Celtic skipper was not fooled by his side's ropey defensive display and pointed the finger at goalkeeper Fraser Forster and centre-back pairing Daniel Majstorovic and Glenn Loovens - all of whom looked particularly nervy before the goals from Joe Ledley and James Forrest eased the tension.
It was a remarkable show of belligerence from the 20-year-old after he had been thrust into a potentially nervy situation with his side 47 for four, but his fearlessness ultimately proved match-winning, with Australia bowled out for 144.
Summary: Inter Milan clinched a fifth consecutive Serie A crown on Sunday after edging to a nervy final-day victory over Siena.
BARCELONA made it seven trophies out of nine in the Per Guardiola era as they overcame a nervy opening to thrash Real Valladolid, relegated as a result, at the Nou Camp last night and sealed a second successive league title on an exciting last day of the Primera Division season.
It [the Bangalore bombings] definitely made me more nervy.
But a deflected free-kick from Andy Thomson late on for the visitors made it a nervy finish for Shotts.
DINARA SAFINA is the 4-9 favourite to beat Svetlana Kuznetsova in tomorrow's women's French Open final after the Russian duo stumbled through nervy semi-finals at Roland Garros yesterday.