Physiology Lab - Vestibular Function

Question 1

What is the function of the vestibular apparatus in the inner ear?

Answer 1

Maintenance of equilibrium

Provides information about the position of body in space

Question 2

What does the vestibular apparatus consist of?

Answer 2

3 semicircular canals (perpendicular to one another)

Organs - the uricle and saccule

Question 3

What is the function of the vestibular hair cells?

Answer 3

Transduce head movement into vestibular sensation

Question 4

How does the function of vestibular hair cells occur?

Answer 4

Distortion of the stereocilia (hairs) on the cells due to head movement depolarises/hyperpolarises the cells.
This changes neurotransmitter release = alters the rate of firing of the axon associated with each hair cell.

Question 5

What are the otolith organs?

Answer 5

Utricle and saccule

Question 6

What is the function of the utricle and saccule (otolith organs)

Answer 6

Sensitive to gravity - provide information about the position of the head in space
Also respond to other linear accelerations - provide information about movements e.g. running, jumping, falling

Question 7

What is the function of the semi circular canals?

Answer 7

Respond to accelerations due to rotational movements of the head

Question 8

Describe the sensory information involved in the co-ordinated reflex for balance and posture.

Answer 8

1 - signals from muscles, joints and skin
2 - visual inputs
3 - vestibular system inputs provide information about body position and movement

Question 9

What are the efferent outputs of balance and posture?

Answer 9

Alpha motor neurons which project their axons to the muscles

Question 10

Name the simple balance tests.

Answer 10

Sharpened Romberg

One-leg stand

Question 11

Name the uses of the vestibular information.

Answer 11

1 - contributes to our conscious awareness of the position of our head in space, speed and direction of acceleration of our head
2 - provides information allowing the neck muscles to maintain the head in its usual positiion
3 - input to coordinating centres in the brain stem & cerebellum involved in maintaining balance and posture
4 - input to extraocular muscles of the eye - this ensures retinal images are kept stable = ocular counter rolling and vesibulo-ocular reflexes

Question 12

What is ocular-counter rolling?

Answer 12

Eyeball rotates counter to the direction of head movement

Question 13

What mediates the ocular counter rolling? (VOR)

Answer 13

The brainstem with inputs from the vestibular system and outputs via the extra-ocular muscles
= the vestibulo-ocular reflex (VOR)

Question 14

What do the eye movements gathered by the VOR allow?

Answer 14

Allow visual fixation - maintain fixation on an object even if your head is moving

Question 15

What is nystagmus?

Answer 15

If the head movement exceeds a certain amount then the slow compensatory eye rotation is interrupted by a quick movement in the opposite direction (i.e. same direction as head movement).
= alternation of slow and quick movements
INVOLUNTARY CYCLICAL MOVEMENT OF THE EYEBALL

Question 16

With what movements is nystagmus most clearly seen?

Answer 16

Angular movements

Named from the quick phase

Question 17

What combinations cause nystagmus when a subject is rotated in light?

Answer 17

Optokinetic nystagmus and vestibular nystagmus

Question 18

What is a sign of neurological dysfunction?

Answer 18

When nystagmus occurs in the absence of any stimuli

Question 19

What structures need to be in tact in order for reflex eye movements and nystagmus to occur?

Answer 19

Semi-circular apparatus and central connections (brainstem)

Question 20

How can we test the neural pathways (particularly the brainstem)?

Answer 20

Looking at vestibular stimulation and observation of resultant eye movements

Question 21

What is caloric testing used for?

Answer 21

Stimulate the vestibular system

Question 22

Describe what happens in caloric testing?

Answer 22

Cold/warm water in ear of supine patient.
The water thus cools/warms the fluid in the adjacent semi-circular canal (endolymph)
This changes its density and fluid moves within the canal
This displaces the cupula and initiates vestibular outputs
If the brainstem is intact, reflex eye movements should be observed
This can determine brainstem death