Canadian Medical Guide > Anatomy > Nervous System > Peripheral Nervous System > Peripheral Nerves > Cranial Nerves Terms and Definitions




Cranial Nerves

Medical Definition: Twelve pairs of nerves that carry general afferent, visceral afferent, special afferent, somatic efferent, and autonomic efferent fibers.
Guide Notes: 1st cranial nerve = OLFACTORY NERVE, 2d = OPTIC NERVE, 3d = OCULOMOTOR NERVE, 4th = TROCHLEAR NERVE, 5th = TRIGEMINAL NERVE, 6th = ABDUCENS NERVE, 7th = FACIAL NERVE, 8th = VESTIBULOCOCHLEAR NERVE, 9th = GLOSSOPHARYNGEAL NERVE, 10th = VAGUS NERVE, 11th =
Cranial Nerves Categories.
Canadian Medical Guide Definition Abducens Nerve - The 6th cranial nerve. The abducens nerve originates in the abducens nucleus of the pons and sends motor fibers to the lateral rectus muscles of the eye. Damage to the nerve or its nucleus disrupts horizontal eye movement control.
Canadian Medical Guide Definition Accessory Nerve - The 11th cranial nerve. The accessory nerve originates from neurons in the medulla and in the cervical spinal cord. It has a cranial root, which joins the vagus (10th cranial) nerve and sends motor fibers to the muscles of the larynx, and a spinal root, which sends motor fibers to the trapezius and the sternocleidomastoid muscles. Damage to the nerve produces weakness in head rotation and shoulder elevation.
Canadian Medical Guide Definition Facial Nerve - The 7th cranial nerve. The facial nerve has two parts, the larger motor root which may be called the facial nerve proper, and the smaller intermediate or sensory root. Together they provide efferent innervation to the muscles of facial expression and to the lacrimal and salivary glands, and convey afferent information for taste from the anterior two-thirds of the tongue and for touch from the external ear.
Canadian Medical Guide Definition Glossopharyngeal Nerve - The 9th cranial nerve. The glossopharyngeal nerve is a mixed motor and sensory nerve; it conveys somatic and autonomic efferents as well as general, special, and visceral afferents. Among the connections are motor fibers to the stylopharyngeus muscle, parasympathetic fibers to the parotid glands, general and taste afferents from the posterior third of the tongue, the nasopharynx, and the palate, and afferents from baroreceptors and chemoreceptors of the carotid sinus.
Canadian Medical Guide Definition Hypoglossal Nerve - The 12th cranial nerve. The hypoglossal nerve originates in the hypoglossal nucleus of the medulla and supplies motor innervation to all of the muscles of the tongue except the palatoglossus (which is supplied by the vagus). This nerve also contains proprioceptive afferents from the tongue muscles.
Canadian Medical Guide Definition Oculomotor Nerve - The 3d cranial nerve. The oculomotor nerve sends motor fibers to the levator muscles of the eyelid and to the superior rectus, inferior rectus, and inferior oblique muscles of the eye. It also sends parasympathetic efferents (via the ciliary ganglion) to the muscles controlling pupillary constriction and accommodation. The motor fibers originate in the oculomotor nuclei of the midbrain.
Canadian Medical Guide Definition Olfactory Nerve - The 1st cranial nerve. The olfactory nerve conveys the sense of smell. It is formed by the axons of OLFACTORY RECEPTOR NEURONS which project from the olfactory epithelium (in the nasal epithelium) to the OLFACTORY BULB.
Canadian Medical Guide Definition Optic Nerve - The 2nd cranial nerve. The optic nerve conveys visual information from the retina to the brain. The nerve carries the axons of the retinal ganglion cells which sort at the optic chiasm and continue via the optic tracts to the brain. The largest projection is to the lateral geniculate nuclei; other important targets include the superior colliculi and the suprachiasmatic nuclei. Though known as the second cranial nerve, it is considered part of the central nervous system.
Canadian Medical Guide Definition Trigeminal Nerve - The 5th and largest cranial nerve. The trigeminal nerve is a mixed motor and sensory nerve. The larger sensory part forms the ophthalmic, mandibular, and maxillary nerves which carry afferents sensitive to external or internal stimuli from the skin, muscles, and joints of the face and mouth and from the teeth. Most of these fibers originate from cells of the trigeminal ganglion and project to the trigeminal nucleus of the brain stem. The smaller motor part arises from the brain stem trigeminal motor nucleus and innervates the muscles of mastication.
Canadian Medical Guide Definition Trochlear Nerve - The 4th cranial nerve. The trochlear nerve carries the motor innervation of the superior oblique muscles of the eye.
Canadian Medical Guide Definition Vestibulocochlear Nerve - The 8th cranial nerve. The vestibulocochlear nerve has a cochlear part (COCHLEAR NERVE) which is concerned with hearing and a vestibular part (VESTIBULAR NERVE) which mediates the sense of balance and head position. The fibers of the cochlear nerve originate from neurons of the SPIRAL GANGLION and project to the cochlear nuclei (COCHLEAR NUCLEUS). The fibers of the vestibular nerve arise from neurons of Scarpa's ganglion and project to the VESTIBULAR NUCLEI.

Cranial Nerves Medical Definitions and Terms

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