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
Q
Describe the arrangement of the labyrinth in the skull
A
- 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
Q
Describe the structure of the utricle and saccule.
A
- 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
Q
What are otoliths?
A
Carbonate cristals on top of the hair cells
28
Q
Describe the vestibular nuclei pathways
A
- 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
Q
Which parts of the cerebellum are involved in the maintenance of balance and control of eye movement?
A
- Vermis
- Flocconodular lobe
30
Q
Describe the activation of the hair cells
A
- 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
Q
Describe the pathway of the vestibuloocular reflex (horizontal)
A
- 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
Q
Which muscles are involved in the vertical vestibuloocular reflex?
A
- Superior rectus muscle and inferior rectus
- Superior oblique and inferior oblique muscle
33
Q
What happens in peripheral unilateral lesions?
A
- 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
Q
Define dizziness
A
The sensation of spinning around and loosing your balance
35
Q
Define vertigo
A
The illusion of movement
36
Q
Define oscillopsia
A
- 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
Q
What is bilateral vestibulopathy?
A
- 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
Q
Describe signalling in the otolith organs
A
- 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
Q
Describe signalling in the semicircular canals
A
- 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
