Neurology 11 - Vestibular System Flashcards
1
Q
Compare type 1 and type 2 hair cells
A
- More type 1 cells
- Type 1 cells have direct afferents and indirect efferents, with a round shape
- Type 2 cells have direct afferents and efferents. More efferents than afferents
2
Q
What are striola?
A
- Opposing hair bundle polarities/direction - the central part of the maculae
- Movement in any direction stimulates a distinct subset of cells
- Two movements from the same stimuli
3
Q
List the components of the semicircular canals
A
- Ampulla (hair cells in the crista) - one side only
- Gelatinous projection - less dense than in the utricle and saccule (cupula)
- Kinocilia (all in the same direction, as cells are oriented in the opposite direction on each side)
4
Q
Describe the blood supply of the vestibular system
A
- Anterior inferior cerebellar artery from the basilar artery gives rise to the labyrinthine artery
- Labyrinthine artery splits to the anterior vestibular artery and common cochlear artery
- Common cochlear artery splits to vestibulococchlear artery and main cochlear artery
- Vestibulocochlear artery splits to form cochlear ramus (joins the cochlear ramus) and posterior vestibular artery which forms arteries of the canals
5
Q
Describe the nervous supply of the vestibular system
A
- Primary afferents end in the vestibular nuclei and in the cerebellum
- Vestibular nuclei - this is where all vestibular reflexes origionate from (superior, lateral, medial and inferior)
- Organised as static labyrinth (otoliths lateral and inferior) and kinetic labyrinth (semicircular canals superior and medial)
6
Q
List the vestibular nuclei projections
A
- Spinal cord
- Nuclei of the extraocular muscles
- Cerebellum
- Centres for cardiovascular and respiratory control
7
Q
List the functions of the vestibular system
A
- Movement coordination (providing spatial reference for other sensory motor co-ordinations)
- Posture regulation
- Tuning cardiovascular function for reorientations
- Perception of motion in space
- Vestibular ocular reflex modulation (compensatory reflexes)
8
Q
List the projections of the vestibular nucleus involving the thalamus and cortex
A
- Vestibular nuclei: project to thalamus
- Thalamic nuclei: project to the head region of the primary somatosensory cortex
- Also to superior parietal cortex: ‘vestibular cortex’ concerned with spatial orientation.
- Cortical projections may account for feeling of dizziness (vertigo) during certain kinds of vestibular stimulation
9
Q
List the functions of the vestibular system
A
- Detect and inform about head movements
- Keep images fixed in the retina during head movements
- Postural control
10
Q
What are the otolith organs?
A
- Utricule and saccule
- Linear acceleration and tilt (otolith movement)
- Depolarisation or hyperpolarisation
- Utricule is horizontal
- Saccule is vertical
11
Q
How do the semicircular canals work?
A
- Respond to angular acceleration by movement of endolymph moving the hair cells. Constant velocity is not felt (inertia).
- Work in pairs (one side is stimulated while the other side is inhibited)
- Both horizontal (lateral)
- Left anterior to right posterior
- Right anterior to left posterior
12
Q
Describe the vestibulospinal reflex pathways
A
- Lateral vestibulospinal tract (ipsilateral, motor neurones to limb muscles)
- Medial vestibulospinal tract (bilateral, motor neurons to the neck and back muscles)
13
Q
What is the function of the vestibulo-ocular reflex?
A
- Keep images fixed while the head is moving
- Connection between the vestibular nuclei and oculomotor nuclei
- 5-7 msec latency
- Eye movement in opposite direction to head movement
14
Q
How are vestibular diagnoses made?
A
- Medical history
- Cranial nerves
- Balance and gait assessment
- Cerebellum
- Gaze assessment
- Vestibular tests (caloric test, vHIT, VEMP, rotational test)
- Imaging (CT/MRI)
- Subjective assessment (questionnaires, useful in long term disease)
15
Q
List the symptoms of vestibular disease
A
- Vertigo (illusion of movement - rotational or true)
- Nystagmus (eye movement, slow movement and fast compensation)
- Dizziness, giddiness
- Unsteadiness
- Self-motion perception
16
Q
Describe the epidemiology of dizziness
A
- 1/4 of people experienced it
- 80% severe enough to see a doctor
1/2 in 75+ - 1/4 referrals to ENT and neurology clinics
17
Q
Where are peripheral vestibular disorders located?
A
- Labyrinth and VIII nerve (vestibulococclear)
- Vestibular neuritis
- Benign paroxysmal positional vertigo
- Menieres disease
- Bilateral vestibular failure
- Unilateral vestibular failure
18
Q
Where are central vestibular disorders located?
A
- CNS
- Stroke, MS, tumours
19
Q
Describe the evolution of vestibular disorders
A
- Acute (vestibular neuritis and stroke)
- Intermittent (benign paroxysmal positional vertigo)
- Recurrent (Menieres disease, migraine)
- Progressive (aucoustic neurona, degeneration)
20
Q
What else, other than vestibular disease, can cause dizziness?
A
- Heart disorders
- Presyncopal episodes
- Orthostatic hypotension
- Anaemia
- Hypoglycaemia
- Psychological
- Gait disorders
21
Q
What is the vestibular system?
A
- Everything there is to balance
- Inputs are visual, rotation and gravity (inner ear), and pressure (proprioception)
- Output is the ocular reflex and postural control
22
Q
What is the outer ear?
A
- What you see
- Eardrum, bones and ausicles
23
Q
What is the labyrinth?
A
- The inner ear
- It is in the petrous part of the temporal bone (hardest bone of the body)
- Cochlear part and vestibular part
- 5 structures generate the vestibular organ
24
Q
Describe the structure of the vestibular organ
A
- 2 otoliths called the utricle and sacculus
- Sacculus is connected to the cochlea and utricule is connected to the sacculus.
- Posterior, anterior and lateral semicircular canals.
- Each semicircular canal has an ampulla
- Fluid is inside the ear (function is to move the hair cells in response to sound, and also change in movement)
25
Describe the arrangement of the labyrinth in the skull
- Cochlear is anterior
- Semicircular canals are lateral
- Anterior (also called superior) canals are 45 degrees
- Posterior (also called inferior) canals are 45 degrees apart
26
Describe the structure of the utricle and saccule.
- Utricle (inferior - detects movement of the horizontal plane) and saccule (cochlear side - transduce movement of vertical plane)
- The rest of the utricle and saccule contrain onle liquid
- Macule (has the hair cells)
- Gelatinous matrix is on top of the hairs - helps to move the hairs
- Otoliths are on top of the gel matrix
27
What are otoliths?
Carbonate cristals on top of the hair cells
28
Describe the vestibular nuclei pathways
- Hair cells send signals to vestibular nuclei to generate spinal reflexes (vestibulospinal tract - limb and trunk and upper back and neck)
- Also goes to cortex (ventroposterior nucleus to vestibular cortex)
- Vestibulo-ocular reflex (oculomotor, abducens and trochlear)
- Cerebellum (vestibulocerebellar reflexes)
29
Which parts of the cerebellum are involved in the maintenance of balance and control of eye movement?
- Vermis
| - Flocconodular lobe
30
Describe the activation of the hair cells
- Stimulus causes movement of the hair cells
- Influx of potassium
- Depolarisation
- Calcium influx and neurotransmitter release
- Resting discharge
- Inhibition and excitation affect the rate of discharge
31
Describe the pathway of the vestibuloocular reflex (horizontal)
- Information comes from the vestibular nucleus to both sides, telling you which way the head is moving
- The side the head moves towards has an increase in frequency
- 3rd and 6th cranial nerves are stimulated (abducens and oculomotor nerve)
- One muscle is stimulated and the other is inhibited
32
Which muscles are involved in the vertical vestibuloocular reflex?
- Superior rectus muscle and inferior rectus
| - Superior oblique and inferior oblique muscle
33
What happens in peripheral unilateral lesions?
- No resting discharge from one side of the labyrinth
- Therefore, the brain thinks that the head is moving towards the direction of the discharge
- The eyes are therefore moved towards the opposite side
- The eyes say the head is not moving, this results in movement of the eye from one side to the other (slow movement with fast compensation)
34
Define dizziness
The sensation of spinning around and loosing your balance
35
Define vertigo
The illusion of movement
36
Define oscillopsia
- Can be caused by nystigmus
- Jumping vision and trouble focusing
- Inability to hold images steady - objects look like they are moving even when they are stationary
37
What is bilateral vestibulopathy?
- Vestibular system of both inner ears is damaged
- Symptoms include imbalance (which is worse in the dark) and visual disturbance
- Oscillopsia occurs when the head is moving (objects appear to be moving when they are not moving)
38
Describe signalling in the otolith organs
- Macula of the utricle and saccule contain vestibular hair cells (each have a kinocilium, which is a long sterocilia, and sterocilia)
- Stereocilia project to the otolithic membrane (a calcium bicarbonate cristal filled gel layer - otoconia)
- Vestibular hair cells synapse with the vestibular nerve
- When gravity pulls down the otoconia/linear acceleration moves them, this moves the stereocilia and kinocilium projecting into the layer as well
- This opens ion channels and causes depolarization thereby creating an AP (depending)
- Gives an idea of linear acceleration and gravitational head position
39
Describe signalling in the semicircular canals
- Each filled with endolymph
- When you move your head to the left the SCC will move the same direction but the fluid will move to the right
- This moves the cupula, a structure in the ampulla of each SCC containing vestibular hair cells thereby stimulating the vbestibular nerve
- Gives an idea of angular acceleration
