Vestibular System - Balance

Question 1

What is the vestibular system?

Answer 1

A sensory system essential for control of posture and balance
Found in inner ear, is series of fluid filled membranous tubes (labyrinths) which are embedded in temporal bone

Question 2

What does the vestibular apparatus consist of?

Answer 2

3 semi-circular canals, the utricle which the semi-circular canals attach to and saccule
Swelling at base of semi-circular canals are the ampulla which contain sensory hair cells
Utricle and saccule contain sensory hair cells

Question 3

What is the function of the semi-circular canals, utricle and saccule?

Answer 3

SC - rotational acceleration
Saccule - vertical acceleration
Utricle - back/front tilt and horizontal acceleration

Question 4

What are the otolith organs?

Answer 4

Utricle and saccule

Question 5

Describe the sensory receptors in the semi-circular canals

Answer 5

Sensory cells are embedded in the ampulla
Inside ampulla are hair cells which act as sensory receptors
Hair cells are embedded in flexible gelatinous structure called cupula which stretches along entire length of ampulla - becomes distorted by endolymph fluid

Question 6

What do the cilia of hair cells synapse with?

Answer 6

Synapse directly with sensory neurons of vestibular nerve (CNVIII)

Question 7

How does semi-circular canals detect rotational acceleration?

Answer 7

If skull rotated left or right from rest then endolymph at first does not move due to inertia
Ampulla moves instantly as it is embedded in skull

Question 8

What does inertia of the endolymph cause?

Answer 8

Produces drag which bends the cupula and the cilia embedded in it, in oppisite direction of movement
If rotation is constant velocity then endolymph catches up and rotates at same speed

Question 9

What does sudden stop after rotation cause for the endolymph?

Answer 9

Endolymph continues to move die to momentum so continuing a sense of movement and dizziness

Question 10

What are the 2 types of cilia of hair cells?

Answer 10

Large kinocilium
Small stereocilia

Question 11

What does distortion of cilia in direction of kinocilium cause?

Answer 11

Depolarisation and increased discharge of APs in vestibular nerve

Question 12

What does distortion of cilia away from kinocilium lead to?

Answer 12

Hyperpolarisation and decreased discharge of APs in vestibular nerve

Question 13

What does kinocilium allow brain to do?

Answer 13

Determine movement in time and space
Brain can use can build 3D image of body position using pattern of firing and inhibition received
Most of the sensory info takes place in cerebellum

Question 14

What is the maculae?

Answer 14

Sensory apparatus of utricle and saccule

Question 15

How are the macula orientated in the utricle and saccule?

Answer 15

Utricle - on the horizontal plane
Saccule - on the vertical plane

Question 16

Describe the structure of the maculae

Answer 16

Have a set of cilia - one kinocilium, a series of stereocilium which protrude into gelatinous mass called otolith membrane
Embedded in otolith membrane is CacO3 crystals called otoliths

Question 17

How is a tilt of head detected in macula in utricle?

Answer 17

In horizontal plane
otoliths have greater density than endolymph so affected more by gravity
Tilting head moves otoliths and membrane
Distorts jelly and moves cilia

Question 18

What does backwards tilt cause?

Answer 18

Moves otolith in direction of the kinocilium causing depolarisation and increased discharge of APs
Oppisite for forward tilt

Question 19

What does vertically orientated macula in saccule respond to?

Answer 19

Vertical forces - elevation in lift and provides info on orientation when lying down

Question 20

What all keeps the brain informed about body’s position in space and direction of movement?

Answer 20

3 ampulla of semi-circular canals and 2 maculae of otolith organs to brain via vestibular nerve

Question 21

How does vestibular nerve help coordinate postural muscles?

Answer 21

Connect vestibular nerve by neural pathways to cerebral centres without synapsing in the medulla

Question 22

What stimulates vestibular nuclei in brainstem?

Answer 22

Afferents from semi-circular canals and otolith organs
Proprioceptors in limbs, trunk, neck and head

Question 23

Where does the vestibular nuclei in brainstem send info?

Answer 23

Descending spinal motor pathways
Cerebral cortex
Extraocular nuclei
Cerebral centres - also afferents can send directly

Question 24

What do the vestibular system reflexes involve?

Answer 24

Vestibulocortical and vestibulospinal tracts
Tonic labyrinthine reflex, vestibulo-ocular reflex and dynamic righting reflexes

Question 25

Explain the tonic labyrinthine reflex

Answer 25

Keeps the axis of head in a constant relationship with rest of body
Uses information from maculae and neck proprioceptors

Question 26

Explain the dynamic righting reflex

Answer 26

Rapid postural adjustments that are made to stop you from falling
Long reflexes involving extension of all limbs

Question 27

Explain the vestibulo-ocular reflex

Answer 27

Strong association is evident between vestibular apparatus, visual apparatus and postural control
In medullary vestibular nuclei - vestibular system synapse with afferent fibres travelling to extraocular nuclei

Question 28

What is the function of vestibular nystagmus?

Answer 28

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

Question 29

Explain the vestibular nystagmus

Answer 29

When eyeball comes to end of range of movement, it rapidly flicks back to starting position
If rotation continues the slow phase starts again, then flicks back
Right rotation then right nystagmus

Question 30

How can nystagmus be used to check vestibular function?

Answer 30

Caloric stimulation - test for horizontal SCC
Temp effects endolymph
Warm fluid - nystagmus towards effected side
Cold fluid - nystagmus away from effected side
COWS

Question 31

How does motion sickness occur?

Answer 31

If visual and vestibular system inputs to cerebellum are in conflict
Cerebellum generates signal to hypothalamus - ANS changes so nausea, vomiting, decrease BP, dizziness, sweating and pallor

Question 32

What is labyrinthitis?

Answer 32

Acute interference with normal vestibular function as result of infection
All ANS symptoms and vertigo

Question 33

What is vertigo?

Answer 33

Perception of movement in absence of movement
Gross impairment of posture and balance

Question 34

Describe Meniere’s disease

Answer 34

Vertigo, nausea, nystagmus, and tinnitus
Associated with overproduction of endolymph causing increase pressure