Vestibular system Flashcards
1
Q
what contributes to orientation
A
- vision (visual space)
- vestibular system (inertial space)
- proprioception (internal space)
2
Q
what is vision
A
- is ambiguous - depends on expectation - cannot tell us anything in isolation. requires validation by vestibular system
- is very good for detecting motion - optic flow
- problems of detecting motion / self motion / circular / linear / roll vection
- tends to dominate - fairground illusions - cinema versions
3
Q
what are the otolith organs and semicircular canals
A
- detect movements in any direction
- otoliths: linear acceleration / tilt
- canals: angular velocity
4
Q
what are hair cells (cilia)
A
- otoliths and canals contain sensory hair cells
- movement causes deflection of hair
- motion towards stereocilium depolarises receptor and increases firing rate of afferent
5
Q
what is the push-pull action of left-right signals
A
- rotation / acceleration is signalled by difference in firing rate between the two ears
- lose one ear - strong sense of rotation cause vertigo and dizziness
6
Q
what is the structure of utricle and saccule
A
- contains endolymph
- receptors in the macula
- utricle - approx horizontal
- saccule - approx vertical
- respond to acceleration (and gravity)
- systematic variation in direction of polarisation
- slow adaptation
- main role postural stabilisation
7
Q
what are the roles of the otolith organs (utricle and saccule)
A
- with head upright: utricle roughly horizontal, saccule vertical
- detect tilt / linear acceleration. cells orientated in all directions to pick up any movement
8
Q
affects of tilt ambiguity
A
- somato-gravic illusion - produces ‘false climb’ illusion in aircraft
- false climb illusion very dangerous for pilots - intuitive response is to pitch the aircraft downwards causing a crash into the sea / land
- pilots must ignore sensations and rely on instruments
9
Q
what are semicircular canals
A
- canals are perpendicular to each other
- therefore detect rotation in any direction
10
Q
why are the cupula neutrally buoyant
A
- normally the cupula is the same density as the surrounding endolymph fluid i.e. it is neutrally buoyant
- therefore does not respond to changes in orientation (e.g. when lying down)
11
Q
what is positional alcohol nystagmus
A
- normally, the cupula should be neutrally buoyant with respect to surrounding fluid
- after alcohol ingestion, the cupula becomes lighter than the surrounding fluid. therefore rises when lying down
- produces a left-beating nystagmus when lying on left ear
- after heavy water (D^2O) ingestion, the cupula becomes heavier than the surrounding fluid. therefore sinks when lying down
- produces a right-beating nystagmus when lying on left ear
12
Q
what is the vestibular ocular reflex
A
- stabilisation of gaze is achieved via vestibular input from both sides of head
- canals operate in a ‘push - pull’ manner
- head rotation causes excitation on one side, inhibition on the other
- asymmetry of firing rate from both ears is the key signal of rotation
13
Q
what is caloric vestibular stimulation
A
method of modulating the firing rate of the primary vestibular afferents, by irrigation of the ear canal with warm or cold water
14
Q
what effect does the vestibular system have on comatose patients
A
- reflex eye movements evoked by caloric vestibular stimulation indicate integrity of the brainstem and can be used for outcome prediction
- 92% of patients with abolished reflex eye movements died
- 67% of patients with normal response had good recovery
15
Q
what is the site of activation
A
GVS bypasses end organs
