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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 Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A bundle of nerve fibers or processes held together by connective tissue.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


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.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Surgical procedure, presence of the malleus handle and chorda tympani nerve, and middle ear mucosal status were also not significant predictors of successful hearing in our study.
The chorda tympani nerve courses through the middle ear and is thus susceptible to damage during ear surgeries, such as stapedectomy [sup][1] and cochlear implantation.
Sectioning or stretching of chorda tympani nerve caused transient disturbance of taste which recovered in 3-4 months.
In our case, sacrifice of the chorda tympani nerve or repeated stimulation of the dehiscent bifid facial nerve might have provided the stimuli for viral reactivation.
* However, if your patient already has a damaged or cut chorda tympani nerve in the other ear, or if you don't know the status of the nerve in the other ear, it is better to terminate the procedure than to take a chance of damaging the chorda tympani in the ear currently being operated on.
A second plaque of tympanosclerosis was seen medial to the neck of the malleus, bridging the gap between it and the cochleariform process and extending to the chorda tympani nerve. Once the ossicular chain mobilized, a round window reflex could be elicited.
In the 98 cases in which scutum-lowering was performed, no damage to the ossicular chain or chorda tympani nerve occurred.
The chorda tympani nerve comes off rostrally, courses ventrally to the first pharyngeal pouch, and enters the mandibular arch.
The nervus intermedius is a clear-cut anatomic structure of approximately the same diameter as the chorda tympani nerve. It crosses over as a separate nerve from the superior vestibular nerve to the facial nerve.
The position of the chorda tympani nerve is abnormally inferior.
The obvious abnormality is the short, thick, vertically placed manubrium of the malleus and the inferiorly placed chorda tympani nerve. The chorda tympani nerve is seen through the tympanic membrane crossing the tympanum at the widest diameter of the tympanic ring.
To elucidate the neural mechanisms of such age-related changes in taste preference and sensitivity, electrophysiological experiments examined taste response characteristics of chorda tympani nerves.