Lab 9 (ƒ 10) - Cranial Nerve Nuclei and Brain Stem Circulation
Cranial Nerve VIII - Vestibulocochlear Nerve
The auditory (cochlear) nerve fibers of the vestibulocochlear (VIII) nerve end in the cochlear nuclear complex. The auditory nerve fibers innervate the receptor cells in the cochlea. Damage to the auditory nerve results in deafness.
The vestibular nerve fibers of the vestibulocochlear (VIII) nerve end in the vestibular nuclear complex. The vestibular nerve fibers innervate the receptor cells in the semicircular canal cristae and the maculae of the utricle and saccule. Unilateral damage of a vestibular nerve results in severe symptoms of vertigo, nystagmus, and visceromotor responses such as nausea, vomiting, and tachycardia, all of which diminish with time.
Clinical test of Cranial Nerve VIII
- Test gross hearing: Speak softly into one ear canal while blocking the other by pressing inward on the tragus. Hide mouth to prevent lip reading, and whisper words like “park,” or “dark” in the unblocked ear, and ask patient to repeat word. Repeat procedure in opposite ear.
- Caloric test: Irrigate ear with cold or warm water and observe eye movements. Not done routinely in conscious patients because of severe visceromotor responses.