Vestibular Systems Flashcards

1
Q

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

A

Semi-circular canals

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2
Q

Which structures in the body sense the acceleration of the headand the strength of gravity?

A

Otolith organs

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3
Q

What are the two otolith organs?

A

Saccule

Utricle

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4
Q

What are the main functions of the vestibular system?

A

Subserve perception of motion in space and tilt (with respect to gravity)
Provide reflex balance reactions to sudden instability of gait/posture (vestibulo-spinal reflexes)
Stabilise the eyes on fixed targets during head movement, preserving acuity (vestibulo-ocular reflexes)
Assist in control of heart rate and blood pressure during rapid up-down tilts
Assist synchronisation of respiration with body reorientations Provokes motion sickness

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5
Q

Define vertigo.

A

False perception of movement in space

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6
Q

Define vestibular ataxia

A

Instability of gait or posture

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7
Q

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

A

Vestibular nystagmus

The eyes start moving in the direction of the lesion

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8
Q

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

A

Oscillopsia

Everything appears to be shaking – the ability to stabilise the eyes is lost

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9
Q

What are some other consequences of vestibular loss?

A

Slight impairment of orthostatic control
Severe nausea and vomiting
Loss of coordination on directional reorientation, motion intolerance, oversensitivity to visual motion in the environment

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10
Q

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

A

Hair cells

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11
Q

Describe the cilia of these hair cells.

A

There is one kinocilium and the rest are stereocilia

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12
Q

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

A

It synapses with a primary neurone dendrite (cell body in Scarpa’s ganglion)
They project to the vestibular nuclei in the brainstem

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13
Q

What stimulates hair cells?

A

In Otoliths: deflection by forces of inertial resistance to acceleration
In Semi-circular Canals: endolymphatic fluid rotation

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14
Q

Describe how the hair cell receptor potential can be changed.

A
Depolarisation = movement towards the kinocilium 
Hyperpolarisation = movement away from the kinocilium
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15
Q

Describe how ganglion cell discharge can be changed.

A

Towards the kinocilium = increased firing frequency

Away from the kinocilium = decreased firing frequency

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16
Q

Describe the orientation and sensitivities of the saccule.

A

Saccule is oriented vertically with the hair cells projecting normal to the plane
They are sensitive in all combinations of vertical and antero-posterior directions

17
Q

Describe the orientation and sensitivities of the utricle.

A

Utricle is oriented almost horizontally with the hair cells projecting vertically
Directional sensitivities in all combinations of lateral and antero-posterior directions

18
Q

How do the otolith organs give a signal of linear acceleration in all 3-dimensional directions?

A

Vector sum of utricular and saccular stimulation patterns gives signal of linear acceleration in all 3-dimensional directions

19
Q

Describe the structure and function of the semi-circular canals.

A

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

20
Q

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

A

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

21
Q

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

A

There is unopposed signal coming from the intact side meaning that there is partial impairment of sensitivity to rotation in the ‘on’ direction of the defunct canal

22
Q

Why would a unilateral canal lesion cause vertigo?

A

The unopposed tonus of the intact canal gives a signal as if the head is rotating to the intact side.
Patient may feel like they’re spinning even though they’re not.

23
Q

Why would acute unilateral vestibular disorder cause vestibular nystagmus?

A

Unopposed tonus of the intact canal causes the eyes to be driven to the lesioned side – this is a vestibulo-ocular reflex (because it thinks that your head is rotating towards the intact side)

24
Q

Where do superior and medial vestibular neurones project?

A

They project to the motor nuclei supplying extraocular muscles.

25
Q

Describe the path of medial vestibular neurones.

A

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 theopposite direction to head rotation)

26
Q

Describe the path of superior vestibular neurones.

A

Project ipsilaterally to the oculomotor and trochlear nuclei to generate
VERTICAL vestibulo-occular reflexes

27
Q

What is oscillopsia?

A

Everything appears to be oscillating
This is due to marked loss of vestibular function impairing eye stabilisation during rapid head movements.
The vestibulo-ocular reflex is lost.

28
Q

How would you test if a patient has oscillopsia?

A

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 target by the head swing.

29
Q

What are the effects of bilateral vestibular disorder on gait?

A

Mild gait ataxia

30
Q

What are the effects of unilateral vestibular disorder on gait?

A

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

31
Q

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

A

Descends ipsilaterally in the ventral funiculus of the spinal cord
Axons terminate in lateral part of ventral horn Influence motor neurones to limb muscles

32
Q

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

A

Descend bilaterally in MLF to cervical and upper thoracic spinal cord
Axons terminate in medial part of ventral horn
Influence motor neurones to back and neck muscles

33
Q

State a common cause of vestibular vertigo that lasts:

a. Seconds
b. Minutes
c. Hours
d. Days
e. Fluctuating/continuous
f. Silent

A
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
34
Q

What is BPPV and how is it treated?

A

Benign paroxysmal positional vertigo
It is caused by otoconial debris in the canals and is provoked by head movement
Debris floating in the canal stimulates the ampulla and generates falsesignals of head rotation
Cured by turning the head vigorously in the opposite direction to that which provokes the vertigo, through 360 degrees, flushing out the debris
Treatment name: particle repositioning manoeuvre