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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 ?
Pain caused by pressure to the Nervus medianus must be clearly distinguished from pain caused by pressure to the lung 10 acupoint at the edge of the Metacarpale I and pain caused by pressure to the large intestine 4 acupoint above the M.
Raymond Mentzer has made the same observation in his study of reformed discipline in Nimes; see "Disciplina nervus ecclesiae," 103-4.
Graham Lee, who enjoyed "the thrill of a lifetime" when finishing third on Amberleigh House in the Grand National, was to be found dancing the night away to the Nervus Rex Band and `Planet 2000' disco on the opposite side of the Pennines on Saturday night.
In addition to the CA, decapitation removes the median neurosecretory cells of the pars intercerebralis (PlC), the corpora cardiaca which serve as paired neurohemal organs for the products of the cerebral neurosecretory cells, intrinsic neurosecretory cells of the corpora cardiaca, and the nervus CA II which contain neurosecretory material.
32) "Uber den Ursprung des Nervus accusticus," Monatsschrift fur Ohrenheilkunde [Journal for Ear Diseases] (1886).
Her argument usefully complements Patricia Parker's essay, "Virile Style," which focuses on the Latin nervus as a keyword in the transmission of the Roman literary tradition that valued a virile, masculine style over a more "effeminate," Ciceronion one.
The cervical plexus consists of the ventral primary divisions of the first four cervical spinal nerves and gives rise to (1) the muscular branches, including the phrenic nerve and nervus descendens cervicalis, as well as (2) the sensory branches, including the lesser occipital, transverse cutaneous, supraclavicular, and great auricular nerves.
Hastamizda bulunan ponsun sol yarisindaki infarkt, muhtemelen trigeminal sinirin traktus spinalis nervus trigeminus cekirdegini etkileyerek sol yuz yarisinda hipoesteziye, traktus kortikobulbaris'i etkileyerek goz bulgularina ve traktus kortikospinalis lateralis'i etkileyerek karsi tarafta motor guc kaybina neden olmustu.