Vestibular Function

Question 1

Describe both vestibular and auditory hair cell structure

Answer 1

The apical membrane of vestibular hair cells contains one tall kinocilium and several shorter stereocilia arranged from shortest to tallest.

Auditory hair cells lack a kinocilium

Basolateral membrane synapses with one or more afferent fibers that project through CN VIII

Question 2

What happens when cilia are bent towards the tallest cillium?

Answer 2

Additional mechanically gated cation channels are opened, further depolarizing the cell

Question 3

Describe the hair cell at rest.

Answer 3

Some mechanically gate cation channels are open, making the cell somewhat depolarized

Question 4

What happens when cilia are bent away from the tallest cillium?

Answer 4

Mechanically gated cation channels are closed, hyperpolarizing the cell

Question 5

Describe the ion composition of the endolymph (fluid bathing the apical surface of the hair cell) and perilymph (fluid bathing the basolateral membrane).

Answer 5

Endolymph: High in K, Low in Na

Perilymph: Low in K, High in Na

Question 6

What type of current occurs when the mechanically-gated cation channels are opened due to cilia bending?

Answer 6

Inward current carried by K and Ca

Question 7

What occurs when the basolateral membrane is depolarized?

Answer 7

Opening of voltage-gated calcium channels, triggering influx of calcium and subsequent exocytosis of synaptic vesicles containing glutamate

Question 8

How is the rate of afferent fiber firing determined?

Answer 8

By the amount of glutamate released by the hair cells.

There is a tonic level of firing in the unstimulated state, and this firing increases or decreases in response to the degree of bending of the cilia in the hair cells

Question 9

What organs are sensitive to linear acceleration?

Answer 9

Urticle and Saccule

Question 10

What organs are sensitive to rotational acceleration?

Answer 10

Semicircular canals

Question 11

What are otoliths or otoconia?

Answer 11

Calcium carbonate crystals located on the endolymph that generate shearing forces during linear movements of the head

Question 12

What is the macula?

Answer 12

Sensory epithelium within the utricle and saccule

Composed of vestibular hair cells and surrounding support cells

Question 13

What is the striola?

Answer 13

A dividing line on tha maculae where hair cell polarity (orientation of the cilia) abruptly changes

Question 14

What is the significance of the transition of hair cell polarity and the curved surface of the maculae?

Answer 14

Ensures that all possible directions of linear acceleration are represented

Question 15

What direction is the utricle more sensitive to?

Answer 15

Horizontal plane

Front-back, Left-Right

Question 16

What direction is the saccula most sensitive to?

Answer 16

Vertical plane

Up-down, Front-Back

Question 17

What are the ampulla, crista, and cupula of the semicircular canals?

Answer 17

Ampulla: Swelling of the base of the semicircular canal

Crista: Sensory epithelium within the ampulla

Cupula: Gelatinous mass over the crista where hair cell cilia extend into

Question 18

What occurs during the rotation of the head in paired canals?

Answer 18

The cupulas are deformed in opposite directions in paired canals, producing opposite changes in hair cell membrane potential

The hair cells in the canal towards which the head is rotating are depolarized

Question 19

What are the pairs of semicircular canals?

Answer 19

Left horizontal vs right horizontal

Left anterior vs. right posterior

Right anterior vs. left posterior

Question 20

What is vestibular adaptation?

Answer 20

Semicircular canals respond to angular acceleration and therefore, their output adapts during constant velocity rotation