4. Origin and Functions of Cranial Nerves
- The 12 pairs of cranial nerves primarily serve the head and neck.
- Only one pair (the vagus nerves) extends to the thoracic and abdominal cavities.
- The cranial nerves are numbered in order, and in most cases their names reveal the most important structures they control.
The first letter of each word in the saying (and both letters of “ah”) is the first letter of the cranial nerve to be remembered: “Oh, oh, oh, to touch and feel very good velvet, ah.”
Table 3- Origin and Functions of Cranial Nerves
|I. Olfactory||Fibers arise from olfactory receptors in the nasal mucosa and synapse with the olfactory bulbs (which, in turn, send fibers to the olfactory cortex)||Purely sensory; carries impulses for the sense of smell|
|II. Optic||Fibers arise from the retina of the eye and form the optic nerve. The two optic nerves form the optic chiasma by partial crossover of fibers; the fibers continue to the optic cortex as the optic tracts||Purely sensory; carries impulses for vision|
|III. Oculomotor||Fibers run from the midbrain to the eye||Supplies motor fibers to four of the six muscles (superior, inferior, and medial rectus, and inferior oblique) that direct the eyeball; to the eyelid; and to the internal eye muscles controlling lens shape and pupil size|
|IV. Trochlear||Fibers run from the midbrain to the eye||Supplies motor fibers for one external eye muscle (superior oblique)|
|V. Trigeminal||Fibers emerge from the pons and form three divisions that run to the face||Conducts sensory impulses from the skin of the face and mucosa of the nose and mouth; also contains motor fibers that activate the chewing muscles|
|VI. Abducens||Fibers leave the pons and run to the eye||Supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally|
|VII. Facial||Fibers leave the pons and run to the face||Activates the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste buds of anterior tongue|
|VIII. Vestibulocochlear||Fibers run from the equilibrium and hearing receptors of the inner ear to the brain stem||Purely sensory; vestibular branch transmits impulses for the sense of balance, and cochlear branch transmits impulses|
|IX. Glossopharyngeal||Fibers emerge from the medulla and run to the throat||Supplies motor fibers to the pharynx (throat) that promote pharynx (throat) that promote swallowing and saliva production; carries sensory impulses from taste buds of the posterior tongue and from pressure receptors of the carotid artery|
|X. Vagus||Fibers emerge from the medulla and descend into the thorax and abdominal cavity||Fibers carry sensory impulses from and motor impulses to the pharynx, larynx, and the abdominal and thoracic viscera; most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity|
|XI. Accessory||Fibers arise from the superior spinal cord (C1–C5)* and travel to muscles of the neck and back||Mostly motor fibers that activate the sternocleidomastoid and trapezius muscles|
|XII. Hypoglossal||Fibers run from the medulla to the tongue||Motor fibers control tongue movements; sensory fibers carry impulses from the tongue|
|Explanation is available on
Origin and Functions of Cranial Nerves