Auditory System III (Vestibular System)

Question 1

What is the vestibular apparatus and what is its function?

Answer 1

Series of membranous fluid-filled tubes that detect changes in motion and position of the head (including acceleration and deceleration)

Question 2

What is the function of the three semicircular canals?

Answer 2

Detection of angular acceleration

Question 3

What is the function of the otolith organs?

Answer 3

Utricle, saccule

Linear acceleration

Question 4

What is the information from the vestibular system used for?

Answer 4

Control of eye movements, maintenance of posture, perception of body position and movement

Question 5

How do the semicircular canals work?

Answer 5

• Each canal contains hair cells in a thickened segment of the canal called the ampulla
• The cupula is a gelatinous mass that encases the stereocilia of hair cells, with the base and tip being attached to the wall of the ampulla
• Rotation of the head causes rotation of the canal but the fluid in the canal does not move - the force imposed on this stationary fluid distorts the cupula and bends the stereocilia

Question 6

How do the stereocilia in the semicircular canals transmit information?

Answer 6

• Hair cells synapse with afferents that form the vestibular nerve
• Larger accelerations cause more bending of stereocilia (due to more movement of canal)
• The hair cells at the centre of the cupula are most sensitive to acceleration (greater acceleration recruits more hair cells towards periphery)
• Direction of acceleration (bend towards longest = depolarization = stimulation; bend away from longest = hyperpolarization = inhibition)
• More depolarization (or hyperpolarization) of hair cells depending on direction of acceleration (deceleration = negative acceleration)

Question 7

Difference between the saccule and utricle in the Otolith organ

Answer 7

Saccule detects the vertical plane of linear acceleration; utricle detects the horizontal plane of linear acceleration

Question 8

What are the otoliths?

Answer 8

• Calcium carbonate crystals embedded in a gelatinous mass
• Otoliths add weight to the gelatinous mass
• Otoliths bend the stereocilia
• During acceleration, otoliths are left behind and bend the stereocilia
• At a constant speed, otoliths catch up and stereocilia are no longer bent
• During deceleration, otoliths keep moving due to their inertia and bend stereocilia in opposite direction

Question 9

What is the purpose of the vestibulo-ocular reflex?

Answer 9

Stabilization of the visual image on the retina of the eye when the head rotates (eyes rotate at the same speed, but in the opposite direction)

Question 10

What is the vestibulo-ocular reflex mediated by?

Answer 10

Brainstem nuclei (input from vestibular system, output to muscles of the eye)

Question 11

What is Meniere’s disease?

Answer 11

Condition that affects the inner ear, causing tinnitus, vertigo, and complete/partial hearing loss
Caused by increased pressure in the inner ear due to problems with either the production or reabsorption of endolymph affecting both the auditory and vestibular systems