Vestibular Function

Question 1

what is the vestibular system

Answer 1

Sensory system in control of posture and balance

Question 2

Where is the vestibular system found

Answer 2

The inner ear. Series of fluid-filled membranous tubes (labyrinths) embedded in the temporal bone

Question 3

What does the vestibular apparatus consist of

Answer 3

3 semi-circular canals, ampulla, utricle (semi-lunar canals connect to this), saccule

Question 4

Where are the sensory hairs found

Answer 4

Ampulla
(Utricle and saccule have similar sensory hairs)

Question 5

What movement does the utricle detect

Answer 5

Back/front tile and horizontal acceleration (e.g. in the car)

Question 6

What movement does the saccule detect

Answer 6

Vertical acceleration (e.g. in lift)

Question 7

What movement does the semi-lunar canal detect

Answer 7

Rotational acceleration (e.g. spinning)

Question 8

What are the hair cells embedded into

Answer 8

Cupula (stretches width of the ampulla)

Question 9

What fluid circulates the semi-lunar canals

Answer 9

Endolymph

Question 10

How does movement of endolymph fluid sent signal back to the brain that you are moving

Answer 10

Movement of Endolymph fluid distorts the cupula - by distorting the cupula the hair cells are distorted which sets up action potential in the vestibular nerve sent back to the brain

Question 11

What is the maculae

Answer 11

Combination of the utricle and saccule

Question 12

What are otoliths

Answer 12

CaCO3 crystals which detect the tilting of the head

Question 13

What is the tonic labyrinthine reflex

Answer 13

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

Question 14

What is the dynamic righting reflex

Answer 14

Rapid postural adjustments that are made to stop you falling when you trip.
Long reflexes involving extension of all limbs (profound in cats)

Question 15

Vestibulo-ocular reflexes

Answer 15

Association between vestibular apparatus, visual apparatus and postural control

Eyes are able to compensate to some extent for a loss of input from vestibular system

Question 16

What is vestibular nystagmus

Answer 16

Movements which rotate the eye against the direction of the head and body so that the original direction of gaze is preserved despite head rotation (think about when going round slow roundabout)

Extent of eye movement restricted by eye movement, when eyeball reaches end of range of motion it rapidly flicks back to starting position (i.e. straight ahead)

R rotation —> R nystagmus

(Often get nystagmus when drunk)

Question 17

How can nystagmus be used to test vestibular function

Answer 17

Outer ear washed with cold or warm fluid, temperature difference from core 37 Celsius sets up convection currents affecting endolymph. Cold causes nystagmus away from affected side, warm towards affect side

COWS - Cold Opposite, Warm Same
Cold into R ear —> L Nystagmus, Warm into R ear —> R Nystagmus

Question 18

What causes motion sickness

Answer 18

Visual and vestibular system inputs to cerebellum in conflict (e.g. vestibular system indicates rotation but visual doesn’t)
Cerebellum generates sickness signal to hypothalamus

Question 19

What symptoms are caused by “sickness signal” from cerebellum to hypothalamus in motion sickness (6)

Answer 19

Autonomic neuropathy symptoms (ANS):
nausea, vomiting, decreased BP, dizziness, sweating and pallor

Question 20

What causes labyrinthitis, what are the symptoms

Answer 20

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

Question 21

What is vertigo

Answer 21

Perception (hallucination) of movement in the absence of movement (may also be nystagmus, impairment of posture and balance)

Question 22

What causes symptoms Ménière’s disease

Answer 22

Over production of endolymph (unknown why) causing increased pressure

Question 23

What are the symptoms of Ménière’s disease (what is the distinguishing feature from labyrinthitis)

Answer 23

Vertigo, nausea nystagmus AND tinnitus (distinguishing feature from labyrinthitis)