Vestibular Function Flashcards
The vestibular system is in control of
posture and balance
What is the vestibular system?
A sensory system
Series of fluid filled membranous labyrinths which are embedded in the temporal bone
Components of the vestibular system
3 semi-circular canals
Utricle
Saccule
Sensory hair cells are contained within what parts of the vestibular system
Utricle
Saccule
Ampulla
How do the otolith organs (utricle and saccule) work?
They detect linear acceleration and encode information about the position of the head in space
Back/front tilt of the head is detected by
the utricle
Vertical movement of the head is detected by
the saccule
The semi-circular canals detect
rotational acceleration
The cupula respond to
movement of the endolymph fluid within the canals
The cilia in the gelatinous cupula detect
rotational acceleration
What are the types of cilia in the gelatinous cupula?
Single large kinocilium
Progressively smaller stereocilia
Distortion of the cilia in the direction of the kinocilium causes
depolarisation and increased discharge off the action potentials in the vestibular nerve
Distortion of the cilia away from the kinocilium causes
hyperpolarisation and decreased discharge of action potentials in the vestibular nerve
Distortion of the kinocilium allows
the brain to determine movement in time and space
The sensory apparatus of the utricle and saccule are collectively known as
the maculae
The macula in the utricle are oriented on what plane?
Horizontal
The macula in the saccule are orientated on what plan?
Vertical
Tilt of the head is detected by
the macula in the utricle
Do otoliths or endolymph have a greater density?
Otoliths - so are subject to a greater force of gravity
What part of the brain co-ordinates the postural muscles required to maintain balance?
Cerebellar centres
Projections from the vestibular nuclei on one side project
ipsilaterally, bilaterally and contralaterally to descending motor pathways
Vestibular nuclei receive input from
proprioceptors signalling limb and body position, and from neck and eye muscles
Vestibular nuclei project via
the thalamus to the cerebral cortex to give perception of movement and body position
What is kinaesthesia?
Conscious awareness of where the body is and its movements
What tracts are involved in the vestibular system reflexes?
Vestibulocortical
Vestibulospinal
Function of tonic labyrinthine reflexes
keep the axis of the head in a constant relationship with the rest of the body using information from maculae and neck proprioceptors
How do dynamic righting reflexes work?
Rapid postural adjustments made to stop you falling when you trip
Long reflexes involving extension of all limbs
How do vestibulo-ocular reflexes work?
Afferents from semicircular canals project and connect to extra ocular nuclei and have strong input to influencing eye movement
Visual system sends powerful descending projections which control posture
How does static reflex work?
When the head is tilted, eyes intort/extort to compensate so that (over a certain range) the image stays the right way up
How does dynamic vestibular nystagmus work?
Series of saccadic eye movements that rotate the eye against the direction of the head and body so that the original direction of gaze is preserved despite head rotating
What is vestibular nystagmus?
Rapid, involuntary eye movements related to a damaged vestibular system
What can be done to test the horizontal semicircular canal?
Caloric stimulation - outer ear washed with cold or warm fluid
Warm fluid causes nystagmus towards
the affected side
Powerful maintained stimulation of the vestibular system can give rise to
kinetosis (motion sickness)
Kinetosis iis most likely to occur if
visual and vestibular inputs to the cerebellum are in conflict
