Vestibular System

Question 1

When are vestibular responses elicited?

Answer 1

Vestibular responses are only elicited when a change in motion occurs. No movement and constant motion are not effective in producing vestibular responses

Question 2

Common vestibular disorders

Answer 2

Meniere’s disease, stationary nystagmus, motion sickness

Question 3

VOR pathways explanation

Answer 3

1. The head turns in one direction (angular change in motion)
2. Receptors of one canal are excited
3. Receptors of the contralateral canal are inhibited
4. Central processing of the sensory inputs from the pair of left & right canals determines direction (which canals are producing information) & velocity (how great is the difference in firing rates)
5. The oculomotor nuclei receive outputs from the vestibular nuclei, and cause the lateral rectus of one eye and the matching medial rectus of the other eye to contract. The antagonists (medial rectus of first eye and lateral rectus of the second eye) relax. The eyes move together to maintain a steady image.

Question 4

The four nuclei making up the vestibular brainstem nuclei are:

Answer 4

1. The lateral vestibular nucleus (a.k.a. Dieter’s nucleus); provides outputs to the cerebellum (feedback) & to lateral vestibulospinal tract to facilitate extensors (posture; muscles of trunk & legs).
2. The inferior vestibular nucleus; outputs to the cerebellum (feedback), to the reticular formation (arousal & ANS; this is an important & often overlooked aspect of vestibular system activity) & to the oculomotor nuclei (c.n. III, IV & VI; VOR).
3. The medial vestibular nucleus; provides descending output to muscles of head & neck via medial longitudinal fasciculus (MLF; head position).
4. The superior vestibular nucleus; provides ascending output (via MLF) to oculomotor nuclei (c.n. III, IV & VI; VOR).

Question 5

Dizziness

Answer 5

a disturbed sense of relationship to space; a sense of unsteadiness, with a feeling of movement within the head

Question 6

Vertigo

Answer 6

illusion of angular or linear movement

Question 7

Ataxia

Answer 7

the failure of gross muscular coordination

Question 8

Disequilibrium

Answer 8

general term describing any form of impaired balance (may require more testing)