Neuro 13: Vestibular Systems

Question 1

Which structures in the body are responsible for angular motion of the head?

Answer 1

Semi-circular canals

Question 2

Which structures in the body sense the acceleration of the head and the strength of gravity?

Answer 2

Otolith organs

Question 3

What are the two otolith organs?

Answer 3

Saccule

Utricle

Question 4

What are the main functions of the vestibular system?

Answer 4

Subserve perception of motion in space and tilt

Provide balance reactions to sudden instability of gait/posture

Stabilise the eyes on fixed targets during head movements

Assist in control of heart rate and blood pressure

Provokes motion sickness

Question 5

Define vertigo.

Answer 5

False perception of movement in space

Question 6

Define vestibular ataxia.

Answer 6

Instability of gait or posture

Question 7

What happens to the ability fo the brain to stabilise the eyes in unilateral vestibular lesions?

Answer 7

Vestibular Nystagmus

eyes move in the direction of the lesion

Question 8

What happens to the ability of the brain to stabilise the eyes in bilateral vestibular lesions?

Answer 8

Oscillopsia
everything appears to be shaking
ability to stabilise the eyes is lost

Question 9

What are some other consequences of vestibular loss?

Answer 9

Slight impairment of orthostatic control
nausea and vomiting
loss of coordination on directional orientation

Question 10

What type of cell is involved in the detection of movement in the vestibular system?

Answer 10

Hair cells

Question 11

Describe the cilia of these hair cells.

Answer 11

One kinocilium and rest are stereocilia

Question 12

What does the hair cell fibre synapse with and where does it project?

Answer 12

synapses with a primary neurone dendrite

project into the vestibular nuclei in the brainstem

Question 13

What stimulates hair cells?

Answer 13

in otoliths - deflection of forces by inertial resistance to acceleration

in canals - endolymphatic fluid rotation

Question 14

Describe how the hair cell receptor potential can be changed?

Answer 14

depolarisation = movement towards the kinocilium

hyperpolarisation = movement away from the kinocilium

Question 15

Describe how ganglion cell discharge can be changed.

Answer 15

Towards the kinocilium = increased firing frequency

Away from the kinocilium = decreased firing frequency

Question 16

Describe the orientation and sensitivities of the saccule?

Answer 16

Saccule is oriented vertically with hair cells projecting normal to the plane

sensitive to all combinations of vertical and antero-posterior directions

Question 17

Describe the orientation and sensitivities of the utricle?

Answer 17

Oriented horizontally with hair cells projecting vertically

sensitive in lateral and antero-posterior directions

Question 18

How do the otolith organs give a signal of linear acceleration in all 3 dimensions?

Answer 18

Vector sum of utricular and saccular stimulation

Question 19

Describe the structure and functions of the semi circular canals.

Answer 19

Hair cells project from the ampulla in the wall of the canal and are
uni-directionally oriented so that acceleration to a particular side
stimulates the canals on that side (e.g. rotation of the head to the right
stimulates the right canal, rotation in the other direction inhibits the right
canal activity)
When head rotation decelerates to a stop, the canal on the other side
(left side) is stimulated

Question 20

Describe the firing of the canals when the head is still.

Answer 20

Each canal has a tonic firing rate so that they equal out when the head is still

Question 21

What are the effects of loss of canal function on one side?

Answer 21

Unopposed signal coming from the intact cide meaning partial impairment of sensitivity to rotation

Question 22

Why would a unilateral canal lesion cause vertigo?

Answer 22

Unopposed tonus of the intact canal gives a signal as if the head is rotating to the intact side

Question 23

Why would acute unilateral vestibular disorder cause vestibular nystagmus?

Answer 23

unopposed tonus of intact canal causes the eyes to be driven to the lesioned side

Question 24

Where do superior and medial vestibular neurones project?

Answer 24

motor nuclei supplying extraocular muscles

Question 25

Describe the path of medial vestibular neurones?

Answer 25

The axons of medial vestibular neurones cross the midline and project
to the contralateral abducens (VI) nucleus to abduct the eye on the
opposite side (in the opposite direction to head rotation)
Axons from the abducens nucleus ascend in the MLF to the
contralateral oculomotor nucleus (III) to adduct the other eye (in the
opposite direction to head rotation)

Question 26

Describe the path of superior vestibular neurones?

Answer 26

project ipsilaterally to the oculomotor and trochlear nuclei to generate vertical vestibulo-occular reflexes

Question 27

What is oscillopsia?

Answer 27

everything appears to be oscillating

Question 28

How would you test if a patient has oscillopsia?

Answer 28

Tell the subject to look at a fixed target and then rapidly move their head

if they have bilateral loss of vestibular function then their eyes will be taken off the target by the head swing

Question 29

What are the effects of bilateral vestibular disorder on the gait?

Answer 29

mild gait ataxia

Question 30

What are the effects of unilateral vestibular disorder on the gait?

Answer 30

tendency for the body and head to lean or fall to the lesioned side

Question 31

Describe the path and function of the lateral vestibulo-spinal tract.

Answer 31

Descends ipsilaterally in the ventral funiculus of the spinal cord

axons terminate in the lateral part of the ventral horn

influence motor neurones to limb muscles

Question 32

Describe the path and function of the medial vestibulo-spinal tract?

Answer 32

descend bilaterally to the MLF

Question 33

State the common causes of vestibular vertigo.

Answer 33

a. Seconds
Benign Paroxysmal Positional Vertigo (BPPV) b. Minutes
Vertebrobasilar insufficiency c. Hours
Meniere’s Syndrome d. Days
Vestibular neuritis e. Fluctuating/continuous
Uncompensated vestibular lesion f. Silent
Acoustic neuroma

Question 34

What is BPPV?

Answer 34

Benign paroxysmal positional vertigo

caused by otoconial debris in the canals and is provoked by head movement

debris floating stimulates the ampulla and generated false signals of head rotation

cured by vigorously turning the head in the opposite direction