Cranial Nerves CNVIII (Vestibulocochlear Nerve)

CN VIII (Vestibulocochlear Nerve)

  Has two branches
Cochlear – hearing
Vestibular – proprioception, understanding where the head is in relation to gravity, tone to anti-gravity muscles, eye movements
1. Cochlear
This is difficult to assess. A crude method is to make a loud, startling sound (a clap), the patient should respond by turning toward the sound, blinking, and moving the ears. Only bilateral loss can be determined in this way, unilateral loss can be missed. Unilateral dysfunction may be assessed only with the use of a special hearing test, the brain stem evoked auditory response (BAER).
2. Vestibular
Physiological nystagmus, also called oculocephalic reflexes or doll’s eye phenomena, is induced by turning the patient’s head back (in a "yes" head movement) and moving the head laterally and medially (in a "no" head movement). The normal response to the oculocephalic test is a quick movement of the eyeball in the direction of the head travel.
Unilateral lesions usually result in nystagmus, ataxia, and a head tilt toward the lesion.