WEEK 8 - Topic 18 - Equilibrium (Cristae Ampullares)

Question 1

What is the crista ampullaris and what is its function?

Answer 1

The crista ampullaris is a sensory receptor organ for dynamic equilibrium and it responds to changes in the velocity of rotational movements of the head.

Question 2

What is the gel-like mass that the hairs extend into? (For the crista ampullaris)

Answer 2

Ampullary cupula

Question 3

What cells does the crista ampullaris consist of?

Answer 3

Hair cells and supporting cells

Question 4

What types of hair does the hair cell have?

Answer 4

Stereocilia and one kinocilium

Question 5

What is the ampullary cupula?

Answer 5

The ampullary cupula is a delicate loosely organised network of gelatinous strands that radiate outwards to contact the hairs of each hair cell.

Question 6

What encircles the base of the hair cells of the crista ampullaris?

Answer 6

Dendrites of the vestibular nerve fibres encircle the base of the hair cells.

Question 7

What happens during rotational acceleration?

Answer 7

1. Because of inertia, endolymph in the semicircular ducts moves in the direction opposite the body’s rotation.
2. The ampullary cupula and hairs bend from the flow of endolymph, depolarising the hair cells.
3. Depolarisation causes increased firing rate of APs to the brain.

Question 8

What happens as the body slows down in rotation?

Answer 8

1. As rotational movement slows, endolymph moves in the direction of rotation.
2. The ampullary cupula and hairs bend in the opposite direction from the acceleration (remember: deceleration is negative acceleration) due to the flow of endolymph, hyperpolarising the hair cells.
3. Hyperpolarisation causes decreased firing rate of APs to the brain.

Question 9

What happens to the endolymph and hair cells when the body is rotating at constant rate?

Answer 9

• Endolymph eventually comes to rest - it moves along at the same speed as the body
• Hair cells are no longer stimulated

Question 10

During rotation, when one ear is depolarised, what happens to the other ear?

Answer 10

Depolarisation occurs in one ear

Hyperpolarisation occurs in the other ear

Question 11

Why does one ear depolarise and the other hyperpolarise during rotation?

Answer 11

Because the axis of the hair cells in one ear is opposite that of the other ear.