Vestibular Function

Question 1

What is the vestibular system?

Answer 1

A sensory system essential in control of posture and balance

Question 2

Describe the vestibular apparatus

Answer 2

3 Semi-circular canals, the utricle, the saccule

Question 3

The ampulla, utricle and saccule contain what?

Answer 3

Hair cells

Question 4

What makes up the otolith organs?

Answer 4

The utricle and saccule

Question 5

What do otolith organs detect?

Answer 5

Linear accelaration and encode info about position of head in space

Question 6

What do SCC’s detect?

Answer 6

Rotational acceleration

Question 7

Where are sensory cells of semi-circular canals embedded?

Answer 7

The ampulla

Question 8

What responds to movement of endolymph?

Answer 8

The cupula

Question 9

Where are the cupula found?

Answer 9

Within the cristae which are within the ampulla

Question 10

What lies within the cupula?

Answer 10

The cilia of hair cells which synapse directly onto CNVIII

Question 11

What happens when the skull is rotated left or right from rest?

Answer 11

Endolymph does not move at first, due to its inertia yet the ampulla moves instantly. Inertia of endolymph produces drag which bends the cupula and its cilia in the opposite direction.

Question 12

If the head is rotated at constant direction, what occurs?

Answer 12

Endolymph catches up and rotates at same speed, removing the shearing forces

Question 13

What occurs if there is a sudden stop in head rotation?

Answer 13

Endolymph will continue to move due to momentum creating a sense of movement and dizziness

Question 14

Name the two types of cilia within the ear?

Answer 14

Kinocilium and stereocilia

Question 15

What happens if cillia is distorted towards the kinocillium?

Answer 15

Depolarisation and increased AP’s in vestibular nerve

Question 16

What happens if cillia is distorted away from the kinocillium?

Answer 16

Hyper-polarisation and decreased discharge of APs in vestibular nerve

Question 17

Why are all cupula angled differently ?

Answer 17

The pattern of firing and inhibition received to each cupula allows the brain to determine the body’s position in time and space

Question 18

What is the sensory apparatus of the utricle and saccule ?

Answer 18

Maculae

Question 19

On which plane do macula lie in the utricle?

Answer 19

Horizontal place

Question 20

On which plane do macula lie in the saccule?

Answer 20

Vertical plane

Question 21

How is cilia arranged within the maculae?

Answer 21

One kinocillium and a series of sternocilium which protrude into the otolith membrane

Question 22

What is embedded within the otolith membrane?

Answer 22

Otoliths, CaCO3 crystals

Question 23

Where do projections from vestibular nuclei on one side project?

Answer 23

Ipsilaterally, bilatterally and contralaterally to descending motor pathways

Question 24

Where do vestibular nuclei receive input from?

Answer 24

Proprioceptors signalling limb and body position and from neck/eye muscles

Question 25

Kinaethesia is achieved by what?

Answer 25

Vestibular nuclei projecting via the thalamus to the cerebral cortex which results in perception of movement and body position

Question 26

What are tonic labyrinthe reflexes?

Answer 26

A primitive reflex which keeps the axis of the head in a constant relationship with the rest of the body

Question 27

What are dynamic righting reflexes?

Answer 27

A reflex which corrects the orientation of the body when it is taken out of the normal upright position. Stops you falling when you trip

Question 28

What is the static reflex?

Answer 28

When you tilt your head, eyes extort/intort to compensate so the image will stay the right way up

Question 29

Describe dynamic vestibular nystagmus

Answer 29

A series of saccadic eye movements that rotate eye against direction of rotation of head and body so direction is gaze is preserved

Question 30

When are you most likely to get symptoms of motion sickness?

Answer 30

When visual and vestibular inputs to the cerebellum are in conflict

Question 31

What happens when there is acute interference with normal vestibular function as a result of infection?

Answer 31

Vertigo

Question 32

What is menieres disease?

Answer 32

Vertigo, nausea, nystagmus and tinnitus due to over production of endolymph