Exam 2: Vestibular

Question 1

Anatomy of the vestibular labyrinth:

Answer 1

Semicircular canals–head angular acceleration (head rotation)
Saccule & Utricle—head linear acceleration (translational motion) & gravity (head tilts)

Question 2

Hair cell arrangement in the ampullae vs. the utricle and saccule:

Answer 2

Semicircular canals: oriented to detect motion around x, y, and z axes
Utricle and Saccule: striola divides hair cells with opposing polarities

Question 3

What type of information is sensed in the saccule and utricle

Answer 3

The otolith organs sense linear acceleration. Hair cells lie in the macula.
When the head tilts the hair cells are distorted by the shift of the otolithic membrane,
The saccule senses acceleration in the vertical plane: Vertical translational movements, Upward or downward head tilts.
The utricle senses acceleration in the horizontal plane: Horizontal translational movements, Sideways head tilts. Hair cells tonically release transmitter, generating spontaneous activity in vestibular nerve fibers.

Question 4

What type of information is sensed in the semicircular canals

Answer 4

Within each ampulla, hair cells oriented with kinocilia pointing in the same direction, Entire population depolarized or hyperpolarized. Canals work in pairs (hair cells aligned oppositely: Left and right horizontal canals. Hair cells in the canal toward which the head is turning are depolarized while the ones on the other side are hyperpolarized. Signals acceleration, deceleration, and constant velocity

Question 5

What is the caloric test & results

Answer 5

Elevate head to 30°above horizontal àhorizontal canals lie in vertical orientation, Warm or cold water generate convection currents that mimic endolymph movement induced by turning head, Net difference in firing rates generates eye movements
Brainstem intact: eye moves other direction fine
MLF lesion: Only one eye moves
Low brainstem lesion: No eyes move they fucked up