Cranial Nerves

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Cranial Nerves


the 12 pairs of nerves that branch off from the anterior (lower) surface of the brain stem in succession from front to back through special openings in the skull. The cranial nerves innervate the organs and tissues of the head and neck, with the exception of the vagus nerve, which descends into the thoracic and abdominal cavities. Cyclostomes, fish, and amphibians normally have only the first ten pairs of cranial nerves.

The first and second pairs of the cranial nerves are the olfactory and optic nerves, which, unlike the other cranial nerves, originate in the brain and serve as conducting pathways for the olfactory and visual analyzers. The third, fourth, and sixth pairs are the oculomotor, trochlear, and abducens nerves; they develop in association with cephalic myotomes and innervate the muscles of the eye. The fifth pair, the trigeminal nerves, is associated with the region of the mandibular arch; the nerves are the chief sensory nerves of the face and serve as the motor nerves of the muscles of mastication. The seventh pair, the facial nerves, innervates the organs of the lateral line and the musculature of the hyoid arch in fish, the superficial musculature of the neck and the muscle that lowers the lower jaw in terrestrial vertebrates, and the facial muscles in humans and simians. The facial nerves also contain secretory fibers to the lacrimal and salivary glands and sensory fibers to the mucous membrane of the tongue. The eighth pair, the vestibulocochlear nerves, evolved from the facial nerves. These nerves are purely sensory: They are responsible for linking the organs of hearing and equilibrium with the brain. The related ninth, tenth, and 11th pairs—the glossopharyngeal, vagus, and accessory nerves—are unequal in fiber composition and extent of spread. The ninth and tenth pairs have motor, sensory, and autonomic components. In mammals the 11th pair arises from the vagus nerve. The accessory nerve is motor to the sternocleidomastoid and trapezius muscles. The 12th pair, the hypoglossal nerves, is unusual in that it arose in amniotes as a result of fusion of the muscular branches of the spinal nerves.

The cranial nerves, unlike the spinal nerves, are not segmented and are highly specialized. Every muscle or group of functionally combined muscles (for example, the masseter muscle) and every organ is supplied only by a single source. Hence, disturbance of nerve conduction, as in paralysis of the facial nerve, cannot be compensated by adjacent nerves. The cranial nerves are nerves of highly specialized sense organs and are regulators of respiration, blood circulation, and digestion.


References in periodicals archive ?
This edition includes head muscles and glands, cervical vertebrae, a resizable interface that conforms to screen size, and extended vessels and cranial nerve content.
Glossopharyngeal neuralgia (GPN) is a rare disorder of the ninth cranial nerve characterized by severe, paroxysmal episodes of pain localized to the posterior tongue, tonsil, throat, or external ear canal (1, 2).
Cranial nerve III (CN III) innervates the superior, inferior, medial recti and the inferior oblique muscles.
The human head has 12 pairs of cranial nerves, which connect the brain with different senses, muscles, glands and organs throughout the body.
This book facilitates understanding of nervous system function with specific sections dealing with sensory and motor functions, functions mediated by the cranial nerves and so-called higher cortical functions.
The mechanisms that account for termination of botulinum toxin action and elimination of toxin from cranial nerves remain unidentified, and the possibility of toxin-induced demyelination cannot be excluded in the patient reported here.
Patients reported to have Garcin's syndrome do not always have unilateral palsies of all cranial nerves; thus, this syndrome was redefined as the presence of at least seven ipsilateral cranial nerve palsies.
It was in course of treating a patient for the cranial nerve disease trigeminal neuralgia who also suffered from Parkinson's Disease that Dr.
Symptoms are generally worse in bilateral cases whilst large neuromas can also involve other cranial nerves, leading to meningiomas and ependymomas.
So to find that cranial nerves - such as those supplying the eye - were degenerating as well was a surprise, Efron says.
It is fairly common practice to report that a patient's cranial nerves are intact, without having examined the first cranial nerve.
For students and professionals in health sciences studying or reviewing the neuroanatomy and gross anatomy of the 12 cranial nerves, Wilson-Pauwels (biomedical communications, U.