The Vestibular System

Question 1

What is the basic function of the vestibular system?

Answer 1

Balance

Question 2

Describe the basic structure of the vestibular apparatus.

Answer 2

There are three semicircular ducts arranged at 90º angles to one another. They are connected to the rest of the inner ear via the utricle.

Question 3

Hair cells of the vestibular system are located in the ________.

Answer 3

ampullae (the enlarged area where the semicircular ducts attach to the utricle)

Question 4

What kind of movement stimulates the saccule?

Answer 4

Vertical movement (the saccule is arranged vertically midway between the utricle and the cochlea)

Question 5

What fluid is inside the semicircular ducts?

Answer 5

Endolymph –same as in the inner ear

Question 6

The superior semicircular canal is also called __________.

Answer 6

the anterior canal

Question 7

The saccule and the ampullae are collectively referred to as __________.

Answer 7

the maculae

Question 8

The vestibular system is located in what bone?

Answer 8

The temporal bone

Question 9

The utricle and the saccule respond to __________ accelerations, while the semicircular canals respond to __________ accelerations.

Answer 9

linear; angular

Question 10

The vestibular system is __________ and _________ to the cochlear.

Answer 10

posterior; lateral

Question 11

The hair cells, floating in the endolymph, are on the _________ side of the membrane.

Answer 11

apical

Question 12

Each hair cell has about 60 to 100 stereocilia. The tallest is called the _________, and it gives the bundle __________.

Answer 12

kinocilium; directional sensitivity

Question 13

Each macula has a gelatinous layer of hair cells covered with ____________.

Answer 13

otoconia (calcium carbonate crystals)

Question 14

True or false: the cupula of the semicircular canals sense constant speed.

Answer 14

False. The cupula adapts to the movement of semicircular fluid and thus only senses accelerations and decelerations.

Question 15

Pushing against the kinocilium (tallest-first direction) leads to ______________.

Answer 15

hyperpolarization and consequent decrease in spontaneous action potentials fired

Question 16

Similar to photoreceptor cells in the eyes, hair cells conduct by _____________.

Answer 16

passive electrical gradient – the afferent nerves fire action potentials

Question 17

Ion channels in hair cells are opened by ____________.

Answer 17

pushing the stereocilia in the excitatory direction, thus causing the tip links to pull open the potassium channels

Question 18

What effect drives nystagmus?

Answer 18

When the head is rotated, one vestibular system is stimulated and the other is inhibited. These signals connect to the oculomotor system, thus promoting compensatory eye movements via the lateral rectus.

Question 19

In the ____________, the axis of polarity changes direction in the middle.

Answer 19

utricle

Question 20

Within each ampullae, there is a patch of epithelium that contains the sensory cells called the ____________.

Answer 20

crista

Question 21

What is the cupula?

Answer 21

A gelatinous mass that the hair cells of the cristae projet into

Question 22

The semicircular canals primarily sense changes in movement because the _____________ moves in relation to the head.

Answer 22

endolymph (which then stimulates the cupula)

Question 23

True or false: at rest roughly 10% of the hair cell cation channels are open.

Answer 23

True! They have a resting firing rate

Question 24

Give the inputs for each of the vestibular nuclei.

Answer 24

Superior and medial: semicircular canals (gaze control)
Lateral: semicircular canals and otoliths (postural reflexes)
Descending: otolith input to integrate vestibular and motor input

Question 25

Describe the basis for the vestibular-ocular reflex.

Answer 25

The semicircular canals send efferents (from the vestibular nucleus) to the medial rectus of the ipsilateral eye and the lateral rectus of the contralateral eye; when the head rotates (sensed by the semicircular canals), the eyes rotate opposite the direction of rotation.