Vestibular System

Question 1

What is the vestibular system comprised off?

Answer 1

3 Semi-circular canals, Utricle, Maccula.

Question 2

Semi-circular Canal features?

Answer 2

All 90 degrees to each other (3 dimesions)
Ampulla: swelling at base of canal, contains sensory hair cells.

Question 3

What are the Otolith organs?

Answer 3

Utricle and Saccula: collective known as the macculae.
Contian otoliths: CaCO3 crystals on otolith membrane.

Question 4

What motion is sensed by each part of the vestibular system

Answer 4

Utricle = front/back tilt + horizontal acceleration
Saccule = vertical acceleration
Semi-circular canals = rotational acceleration

Question 5

Ampulla Structures?

Answer 5

Cupula: gelatinous structure
Hair cells: cilia of the hair cells embedded in cupula. (receptor cells)
Receptor cells directly synapse with the vestibular nerve.
Endolymph: fluid which fills the semicircular canal.

Question 6

Rotational movement detection steps

Answer 6

1. skull rotated, endolymph doenst move due to inertia. Ampulla does move due to being attached to bone
2. inertia causes drag, bending cupula in the opposite direction
   3a. if constant velocity cupula will catch up and rotate at the same speed: takes several seconds
   3b. Sudden stop will cause endolymph to continue to move due to momentum –> dizziness, continued sense of movement.

Question 7

Structures of the hair cells

Answer 7

Kinocillium: very large hair cell
stereocillia: set of gradually smaller hair cells

Question 8

Movement of hair cells and APs

Answer 8

Distortion of cilia towards Kinocillium –> depolarisation, Increased APs discharged
Distortion of cilia away from Kinocillium –> hyperpolarization, decreased discharge of APs

Brain able to determine movement as the orientation of cuppula are different, therefore can make a 3D image from pattern of firing and inhibition.
integreation of this sensory information taken place in the cerebellum.

Question 9

Orientation of utricle and saccule

Answer 9

utricle: horizontal plane
saccule vertical plane

Question 10

Structure of Macculae

Answer 10

Cilia: kinocillium, stereocilium
Gelatinous membrane: otolith membrane
Otoliths: CaCO3 crystals embeded into the otolith membrane.

Question 11

What do the utricle detect?

Answer 11

Head tilt
Backward: depolarisation + increased APs (towards kinocillium)
Forward: hyperpolarisation + decreased APs (away from kinocilium

Question 12

What does the saccule detect?

Answer 12

Vertical forces: elevation in lift, orientation of head when lying down

Question 13

Otolith function

Answer 13

They have a greater density than the endolymph, thus affected more by gravity
head tilt moves otoliths, moves otolith membrane, moves cilia.

Question 14

Where does the sensory information go

Answer 14

Cerebellar centres
Vestibular nuclei in brainstem:
1.descending spinal motor pathways
2.cerebral cortex- awarness of body position
3.extraocular nuclei

Question 15

3 Vestibular System Reflexes

Answer 15

Tonic Labyrinthine reflexes
Dynamic Righting reflexes
Vestibulo-ocular reflexes

Question 16

Tonic Labyrinthine reflex

Answer 16

Keeps the axis of head constant with the body.
Uses information from Maculae and neck Proprioceptors

Question 17

Dynamic righting reflex function

Answer 17

rapid postural adjustments
made to stop you falling when you trip
Long reflexes: involves extension to limbs

Question 18

Vestibulo-ocular reflex function

Answer 18

Vestibular Nystagmus: series of saccadic eye movements that rotate eye against the direction of passive rotation

Question 19

What Nystagmus is caused in right rotation

Answer 19

Right Nystagmus
Right rotation causes eye to drift towards bony orbit on left
leads to Right flick back.

Question 20

Horizontal semi-circular canal test

Answer 20

Caloric Stimulation
Ear washed out with warm or cold fluid: temp difference affects endolymph causing Nystagmus
COWS (Cold opposite, Warm Same)

Question 21

Nystagmus caused by warm water

Answer 21

R ear –> R Nystagmus

Question 22

Nystagmus caused by cold water

Answer 22

R ear –> L Nystagmus

Question 23

Causes of Nystagmus

Answer 23

Lesions to peripheral or central vestibular pathways

Question 24

What is motion Sickness (kinetosis)

Answer 24

When Visual and vestibular system are in conflict
vestibular indicates rotation, visual does not

Question 25

Symptoms of Motion sickness

Answer 25

Cerebellum generates ‘sickness signal’ to hypothalmus causing these.
Autonomic nervous System changes: Nausea, vomiting, decreased BP, Dizziness, sweating and pallor

Question 26

What are the Autonomic nervous system symptoms

Answer 26

Nausea, Vomiting, Blood pressure change (decrease), sweating, pallor, dizziness

Question 27

what is Labyrinthitis

Answer 27

Acute interference with normal vestibular function, Due to infection.
All ANS symptoms + vertigo

Question 28

What is Vertigo

Answer 28

perception (hallucination) of movement in the absence of movement.
There may be Nystagmus, Gross Impairment of Posture and Balance.
Very disabling

Question 29

What is Menieres Disease?

Answer 29

Associated with overproduction of endolymph
Unknown Cause.

Question 30

Presentation of Menieres Disease

Answer 30

Vertigo, Nausea, Nystagmus and Tinnitus=subjective noise (hearing noise that isnt there)

Question 31

How is balance compensated with chronic vestibular impairment

Answer 31

The visual system compensates
Learning circuits set up within the cerebellum, problems occur when patients cannot use visual information