Vestibular System Flashcards
Labyrinth?
Inner Ear!
Protected by the temporal bone
Organs of the Labyrinth?
- Semi-circular canals
o stimulated by ANGULAR acceleration
o gives signal of approx. angular velocity - Otolith organs
o i.e. Saccule & Utricle
o stimulated by LINEAR acceleration and GRAVITY force
o gives signal of head acceleration & tilt
Ampulle?
Semi-circular canals
3 canals at the end of which you find the ampulla
What are the signals received by the Labyrinth used to do?
- Control BALANCE
o dysfunction leads to ataxia - Provide SPATIAL REFERENCE for other motor actions
o dysfunction leads to ataxia - Provide COMPENSATORY REFLEXES
o total loss dysfunction leads to oscillopsia (objects oscillate)
o unilateral loss dysfunction leads to nystagmus - Provide PROPRIOCEPTION
o dysfuntion leads to dizziness - Tune CVS for RE-ORIENTATIONS
o dysfunction leads to dizziness
Unusual stimulation of the balance organs provokes motion sickness!
What 3 types can vestibular disorders be?
- Structural
o destructive OR irritative disease - Functional
o mis-interpretation of sensory input
o mal-adaptation
o loss of rules of correspondence - Both
o structural disorder provoking chronic dysfunction
Disorders of the vestibular system?
Include:
- Vertigo - false perception of movement in space
- Vestibular ataxia - instability of gait & posture
- Vestibular nystagmus - UNILATERAL vestibular lesion
- Oscillopsia - BILATERAL vestibular lesion
- Motion sickness - loss of co-ordination on directional reorientation, oversensitivity to visual motion in the envrionment
- Acute phase of vestibular loss - slight impairment of orthostatic control = severe nausea and vomiting
Otolith Organs?
2 Otolith Organs
- Utricle - senses movement in the HORIZONTAL plane
- Saccule - senses movement in the VERTICAL plane
Anatomy of the Otolith organs?
o Otoconia
- layer of CaCO3 on top of gelatinous layer
- heavy SO movements of the head DISPLCE the otoconia = pulls the hair cells
There is ONE KINOCILIUM per hair cell
o movements TOWARDS it = stimulate cell
o movements AWAY from it = inhibit cell
These cells are OMNI-DIRECTIONAL
Anatomy of semi-circular canals?
3 semi-circular canals
o each join into an ampulla - contains a CAPULA full on hair bundles
Displacement of endolymph in the canals will MOVE the CAPULA
o = fire off APs from the hair cells
CONSTANT tonic firing @ rest
Linear acceleration in the otolith organs and semi-circular canals?
Organ - MOVE the heavy otoconia layer
S-C Cs - produce EQUAL FORCE from eahc side of the capula SO NO net movement
remember stimulated by angular movement
What happens when the head turns left?
- Head turns left
- Movement towards kinocilium in the horizontal canal in the left ear
o BUT away from kinocilium in right ear - SO DP is left ear
o Hyperpolarisation in the right ear
Vestibular-Ocular Reflex
SUPERIOR & MEDIAL vestibular neurons project to motor nuclei supplying the extraocular muscles!
- Axons ascend in MLF (medial longitduinal fusciculus)
- Excite the ipsilateral oculomotor (CN III) nucleus
- Also excite the contralateral abducens (CN VI) nucleus
VOR?
The vestibulo-ocular reflex (VOR) is a reflex, where activation of the vestibular system of the inner ear causes eye movement.
Head-movements to the left in terms of VOR?
Eyes rotate to the R
and
SACCADE (a rapid movement of the eye between fixation points) to the L
VOR acts to maintain gaze on a selected target
Oscillopsia?
Loss of vestibular function impairs eye stabilisation during rapid head movement
o this is as the VOR is the only mechanism to drive fast compensatory reflex
