Vestibular Systems Flashcards
Which structures in the body are responsible for angular (rotational) motion of the head?
Semi-circular canals
Which structures in the body sense the acceleration of the headand the strength of gravity?
Otolith organs
What are the two otolith organs?
Saccule
Utricle
What are the main functions of the vestibular system?
Subserve perception of motion in space and tilt (with respect to gravity)
Provide reflex balance reactions to sudden instability of gait/posture (vestibulo-spinal reflexes)
Stabilise the eyes on fixed targets during head movement, preserving acuity (vestibulo-ocular reflexes)
Assist in control of heart rate and blood pressure during rapid up-down tilts
Assist synchronisation of respiration with body reorientations Provokes motion sickness
Define vertigo.
False perception of movement in space
Define vestibular ataxia
Instability of gait or posture
What happens to the ability of the brain to stabilise the eyes in unilateral vestibular lesions?
Vestibular nystagmus
The eyes start moving in the direction of the lesion
What happens to the ability of the brain to stabilise the eyes in bilateral vestibular lesions?
Oscillopsia
Everything appears to be shaking – the ability to stabilise the eyes is lost
What are some other consequences of vestibular loss?
Slight impairment of orthostatic control
Severe nausea and vomiting
Loss of coordination on directional reorientation, motion intolerance, oversensitivity to visual motion in the environment
What type of cell is involved in the detection of movement in the vestibular system?
Hair cells
Describe the cilia of these hair cells.
There is one kinocilium and the rest are stereocilia
What does the hair cell fibre synapse with and where does it project?
It synapses with a primary neurone dendrite (cell body in Scarpa’s ganglion)
They project to the vestibular nuclei in the brainstem
What stimulates hair cells?
In Otoliths: deflection by forces of inertial resistance to acceleration
In Semi-circular Canals: endolymphatic fluid rotation
Describe how the hair cell receptor potential can be changed.
Depolarisation = movement towards the kinocilium Hyperpolarisation = movement away from the kinocilium
Describe how ganglion cell discharge can be changed.
Towards the kinocilium = increased firing frequency
Away from the kinocilium = decreased firing frequency