Equilibrium + Posture 1 (Vestibular System) Flashcards
What are the 3 main contributors to orientation??
Vision (visual space) Vestibular system (inertial space) Proprioception (internal space)
On a basic level, what is the vestibular system good at in terms of vision?
Very good at detecting motion (optic flow).
Prevalent with fairground illusions
What is the inner ear considered as?
The organ of balance
What are otoliths concerned with??
Concerned with linear acceleration/tilt
What are semicircular canals concerned with?
Concerned with angular velocity
How does movement affect sensory hair cells (exist on both otoliths and canals)
Causes a deflection of the hairs
What do the stereocilia on hair cells do??
Motion towards the stereocilium depolarises the receptor and hence increasing firing rate of the afferent
Discuss the push-pull action of left-right signals.
Rotation or acceleration is signalled by the difference in firing rate between the 2 ears.
Loss of one ear results in a strong sense of rotation causing vertigo and dizziness
Provide a broad description of the utricle and succule structure?
Contain endolymph Receptors in the macula Respond to acceleration and gravity Systematic variation in direction of polarisation Slow adaptation Main role is postural stabilisation
Utricle is approx horizontal when head is upright
Succule is approx vertical when head is upright
The semicircular canals are perpendicular to each other, therefore can what?
Detect rotation in any direction
The cupula is neutrally buoyant, what does this mean??
Typically the cupula is the same density as the surrounding endolmyph fluid, and therefore does not respond to changes in orientation (e.g., when lying down)
What is positional alcohol nystagmus??
Upon alcohol ingestion, the cupula becomes lighter than the surrounding fluid. Therefore rises when laying down - which produces a left-beating nystagmus when lying on left ear
What occurs after heavy water ingestion?? (D20)
The cupula becomes heavier than the surrounding fluid, therefore sinks when lying down -> produces a right beating nystagmus when lying on left ear
How is stabilisation of gaze achieved??
Via vestibular input from both sides of the head
How do the canals operate in unison?
In a push-pull manner, where head rotation causes excitation of one side, inhibition of the other
What is the key signal for rotation of the head??
Asymmetry of the firing rate from both ears
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
What occurs with warm H2o irrigation?
Increased firing mimics head turn towards the irrigated ear
What occurs with cold H2o irrigation??
Decreased firing means mimics head turn away from the irrigated ear
Galvanic vestibular stimulation?
A non-invasive method for altering vestibular nerve activity
Typically bipolar binaural and generally well tolerated, motion sickness is unusual
What is the site of activation of GVS?
GVS bypasses end organs
Wha is the Virtual Signal?
The firing rate of all vestibular afferents is modulated.
The resultant signal of roll about an axis in the Sagital plane directed approx 18. upward from Reid’s plane is predicted
How does GVS evoke torsional eye movements?
Modulated firing rate causes torsional eye movements by activating the VOR
Does the GVS evoke a balance response?
Yes, the direction of the turn is sensitive to the orientation of the head
