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CRANIAL NERVES
| Question | Answer |
|---|---|
| ORIGIN: Fibers arise from olfactory receptors in the nasal mucosa and synapse with the olfactory bulbs | I. Olfactory |
| FUNCTION: Purely sensory; carries impulses for the sense of smell | I. Olfactory |
| TEST: Subject is asked to sniff and identify aromatic substances, such as oil of cloves or vanilla | I. Olfactory |
| ORIGIN: 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 thalamus as the optic tracts; thalamic fibers connect to visual cortex | II. Optic |
| FUNCTION: Purely sensory; carries impulses for vision | II. Optic |
| TEST: Vision and visual field are tested with an eye chart and by testing the point at which the subject first sees an object (finger) moving into the visual field; eye interior is viewed with an ophthalmoscope | II. Optic |
| ORIGIN: Fibers run from the midbrain to the eye | III. Oculomotor |
| FUNCTION: Purely motor; 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 | III. Oculomotor |
| TEST: Pupils are examined for size, shape, and size equality; pupillary reflex is tested with a penlight (pupils should constrict when illuminated); eye convergence is tested, as is the ability to follow moving objects | III. Oculomotor |
| ORIGIN: Fibers run from the midbrain to the eye* | IV. Trochlear |
| FUNCTION: Purely motor; supplies motor fibers for one external eye muscle (superior oblique) | IV. Trochlear |
| TEST: Tested in common with cranial nerve III for the ability to follow moving objects | IV. Trochlear |
| ORIGIN: Fibers emerge from the pons and form three divisions that run to the face | V. Trigeminal |
| FUNCTION: Mixed nerve; conducts sensory impulses from the skin of the face and mucosa of the nose, mouth, and corneas; also contains motor fibers that activate the chewing muscles | V. Trigeminal |
| TEST: Sensations of pain, touch, and temperature are tested with a safety pin and hot and cold objects; corneal reflex tested with a wisp of cotton; motor branch tested by asking the subject to open mouth against resistance and move jaw from side to side | V. Trigeminal |
| ORIGIN: Fibers leave the pons and run to the eye | VI. Abducens |
| FUNCTION: Purely motor; supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally | VI. Abducens |
| TEST: Tested in common with cranial nerve III for the ability to move each eye laterally | VI. Abducens |
| ORIGIN: Fibers leave the pons and run to the face | VII. Facial |
| FUNCTION: Mixed nerve; activates the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste buds of anterior tongue | VII. Facial |
| TEST: Anterior two-thirds of tongue is tested for ability to taste sweet, salty, sour, and bitter substances; subject is asked to close eyes, smile, whistle, etc.; tearing of eyes is tested with ammonia fumes | VII. Facial |
| ORIGIN: Fibers run from the equilibrium and hearing receptors of the inner ear to the brain stem | VIII. Vestibulocochlear |
| FUNCTION: Mixed nerve; vestibular branch transmits impulses for the sense of balance, and cochlear branch transmits impulses for the sense of hearing; small motor component adjusts sensitivity of sensory receptors | VIII. Vestibulocochlear |
| TEST: Hearing is checked by air and bone conduction, using a tuning fork | VIII. Vestibulocochlear |
| ORIGIN: Fibers emerge from the medulla and run to the throat | IX. Glossopharyngeal |
| FUNCTION: Mixed nerve; supplies motor fibers to the pharynx (throat) that promote swallowing and saliva production; carries sensory impulses from taste buds of the posterior tongue and from chemical and pressure receptors of the carotid artery | IX. Glossopharyngeal |
| TEST: Gag and swallowing reflexes are checked; subject is asked to speak and cough; posterior tongue may be tested for taste | IX. Glossopharyngeal |
| ORIGIN: Fibers emerge from the medulla and descend into the thorax and abdominal cavity | X. Vagus |
| FUNCTION: Mixed nerve; 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 | X. Vagus |
| TEST: Tested in common with cranial nerve IX because they both serve muscles of the throat | X. Vagus |
| ORIGIN: Fibers arise from the superior spinal cord (C1–C5)* and travel to muscles of the neck and back | XI. Accessory |
| FUNCTION: Purely motor fibers activate the sternocleidomastoid and trapezius muscles | XI. Accessory |
| TEST: Sternocleidomastoid and trapezius muscles are checked for strength by asking the subject to rotate head and shrug shoulders against resistance | XI. Accessory |
| ORIGIN: Fibers run from the medulla to the tongue | XII. Hypoglossal |
| FUNCTION: Purely motor fibers control tongue movements | XII. Hypoglossal |
| TEST: Subject is asked to stick out tongue, and any position abnormalities are noted | XII. Hypoglossal |
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olympustudies