The vestibular system

Question 1

What are the inputs and outputs of the vestibular system?

Answer 1

Input: visual, pressure, proprioception and gravity
Output: occular reflex and postural reflex

Question 2

Describe the gross structure of the vestibular organs?

Answer 2

There are 5 vestibular organs: utricle, saccule and 3 semicircular canals. All semi-circular canals are connected to the utricle. Anterior and posterior canals come together. Saccule connected to and in between utricle and cochlear.

Question 3

How do you classify liquid in this system?

Answer 3

Inside organs it’s called endolymph, and outside called perilymph.

Question 4

What are the two types of hair cells?

Answer 4

Type 1: more numerous, direct afferents and indirect afferents.
Type 2: direct afferents and efferents

Question 5

What is the maculae and describe where its located?

Answer 5

Maculae is where the sensory hair cells are found. Located in lower part of utricle and side of saccule.
Thus Utricles detect movement in horizontal plane and saccule in vertical due to position of maculae.
Striola is in the centre of the maculae

Question 6

How do hair cells (kinocilia) move?

Answer 6

Hair cells are surrounded by gel and on top of gel are otoliths (crystals). When we move our head the gel moves, then otoliths move so hair cells move.

Question 7

Describe orientation of hair cells in otolith organs?

Answer 7

In utricle hair bundles ace each other in the striola so movement towards striola stimulates cell. In saccule hair bundles face away from each other so deflection away from striola stimulates cell.

Question 8

Describe internal structure of semi-circular canals?

Answer 8

The hair cells are in crista and are connected to nerves. An area called the capula contains a thin gel which surrounds hair cells. Hair cells face same direction. In the horizontal canal hair cells face utricle and in to vertical (A and P) face away from utricle

Question 9

Describe the blood supply and nerve supply of vestibular apparatus?

Answer 9

Blood from inner ear comes from anterior an inferior cerebellar arteries.
The superior vestibular nerve goes to utricle and anterior and horizontal canals. Inferior vestibular nerve goes to saccule and posterior canals.

Question 10

How many vestibular nuclei are there?

Answer 10

4- superior inferior, lateral and medial

Otolith organs go to lateral and inferior and SCC go to medial and superior

Question 11

Where is the vestibular cortex?

Answer 11

In the parietal cortex but cant pinpoint a specific structure.

Question 12

What is the vestibulocerebellar pathway

Answer 12

Coordinates movement, regulates posture and modulates vestibulo-occular reflex

Question 13

What is the function of the vestibular system?

Answer 13

Detect and inform head movement, keep images fixed during head movement and controls posture

Question 14

Describe how movement of hair fibres causes nerve firing?

Answer 14

Nerve fibres give a basal firing rate which can increase or decrease. When hair cells move potassium enters the nerve fibre and you get depolarisation and release of neurotransmitter.

Question 15

How is movement in otolith organs corroborated?

Answer 15

When you get forward and backward head tilt hair cells deflect and depending on which side of striola they lie they get depolarised or hyperpolarised. This provides two inputs on the direction of movement per ear.

Question 16

Describe depolarisation in the SCC?

Answer 16

The endolymph moves in opposite direction to head movement, this moves cupula which moves cells. In the 2 vertical canals movement away from utricle depolarises and in horizontal movement towards the utricle depolarises.

Question 17

whats the relationship between SCC and acceleration?

Answer 17

SCCs only detect changes in velocity. At constant velocity endolymph doesn’t move so hair cells don’t fire.

Question 18

How is movement in SCC corroborated?

Answer 18

SCCs work in pairs….i.e. both horizontals left and right, left anterior with right posterior, left posterior with right anterior. When one side generates a response the other side generates the opposite response so information is corroborated.

Question 19

What are the two main vestibular reflexes?

Answer 19

Vestibulo-spinal reflex which keeps you upright

Vestibulo-occular reflex which coordinates head and eye movement.

Question 20

What are the two vestibular tracts?

Answer 20

Lateral vestibulospinal tract: from lateral vestibular nucleus on ipsilateral side and comes off at Lumbar spine to supply limbs
Medial vestibulospinal tract: bilateral (mainly ipsilateral) and supplies neck and back muscles.

Question 21

Describe the VOR?

Answer 21

When head moves horizontally one horizontal canal will be depolarised and the other hyperpolarised. Depending which one gets depolarised the direction of movement is given. Vestibular nucleus then innervates the relevant extrinsic eye muscles to keep eyes fixed.

Question 22

What would be the effect of a unilateral lesion?

Answer 22

A unilateral lesion will decrease firing rate on the affected side whereas the other side will still fire. This gives impression the head is moving so eyes will move in opposite direction as part of VOR. The yes will attempt to put themselves back but will again move due to VOR- nystagmos.

Question 23

What tools can we use in diagnosis of vestibular disorders?

Answer 23

Assess balance and gait, assess eye movements, imaging, vestibular tests e.g. vHIT and VEMP

Question 24

What are symptoms of vestibular disorders?

Answer 24

Vertigo, dizziness, off balance and lack of proprioception.

Question 25

Give one classification of vestibular disorders?

Answer 25

Central (affects CNS): e.g. stroke, tumours

Peripheral (affects labyrinth and VIII): e.g. vestibular neuritis, vestibular failure

Question 26

Give another classification of disorders?

Answer 26

Acute: vestibular neuritis
Intermittent: BPPV
Recurrent: Meniere’s disease
Progressive: acoustic neuroma (affecting VIII)