cranial nerve

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cranial nerve

Any of several nerves that arise in pairs from the brainstem and reach the periphery through openings in the skull. There are 12 such pairs in mammals, birds, and reptiles and usually 10 pairs in amphibians and fish.
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cranial nerve

Abbreviation: CN
Any of the twelve pairs of nerves that leave the cranial cavity through foramina in the skull and innervate the head. The cranial nerves are numbered in the order they contact the brain; from anterior to posterior, they are the olfactory (CN I), optic (CN II), oculomotor (CN III), trochlear (CN IV), trigeminal (CN V), abducens (CN VI), facial (CN VII), vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), spinal accessory (CN XI), and hypoglossal (CN XII) nerves. The central nuclei for all the cranial nerves, except the olfactory nerve, are in the brainstem. See: illustration


Lesions of the cranial nerves give rise to the following alteration(s): First (CN I; olfactory): Loss of the sense of smell. Second (CN II; optic): Blindness in all or part of a visual field. Third (CN III; oculomotor): Ptosis (drooping) of the eyelid, deviation of the eyeball outward, immobility of the pupil, double vision. Fourth (CN IV; trochlear): Rotation of the eyeball upward and outward, double vision. Fifth (CN V; trigeminal):


Pain or loss of sensation in the face


Weakness of the jaw, difficulty chewing. Sixth (CN VI; abducens): Deviation of the eye outward, double vision. Seventh (CN VII; facial): Paralysis of muscles of facial expression. Eighth (CN VIII; vestibulocochlear): Deafness; ringing in the ears; dizziness; nausea and vomiting; reeling. Ninth (CN IX; glossopharyngeal): Disturbance of taste; difficulty in swallowing; loss of gag reflex. Tenth (CN X; vagus): hoarseness; difficulty swallowing; autonomic disturbances of the viscera.Eleventh (CN XI; spinal accessory): Drooping of the shoulder; inability to rotate the head. Twelfth (CN XII; hypoglossal): Paralysis of the tongue, deviation of the tongue toward one side; thick speech.

See also: nerve

cranial nerve

one of 10 (in ANAMNIOTES) or 12 (in AMNIOTES) peripheral nerves that emerge from the vertebrate brain as distinct from the spinal cord, passing through holes in the skull to innervate structures in the head, neck and upper body.
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