Vestibular Function Flashcards
What is the vestibular system?
A sensory system essential in control of posture and balance
Describe the vestibular apparatus
3 Semi-circular canals, the utricle, the saccule
The ampulla, utricle and saccule contain what?
Hair cells
What makes up the otolith organs?
The utricle and saccule
What do otolith organs detect?
Linear accelaration and encode info about position of head in space
What do SCC’s detect?
Rotational acceleration
Where are sensory cells of semi-circular canals embedded?
The ampulla
What responds to movement of endolymph?
The cupula
Where are the cupula found?
Within the cristae which are within the ampulla
What lies within the cupula?
The cilia of hair cells which synapse directly onto CNVIII
What happens when the skull is rotated left or right from rest?
Endolymph does not move at first, due to its inertia yet the ampulla moves instantly. Inertia of endolymph produces drag which bends the cupula and its cilia in the opposite direction.
If the head is rotated at constant direction, what occurs?
Endolymph catches up and rotates at same speed, removing the shearing forces
What occurs if there is a sudden stop in head rotation?
Endolymph will continue to move due to momentum creating a sense of movement and dizziness
Name the two types of cilia within the ear?
Kinocilium and stereocilia
What happens if cillia is distorted towards the kinocillium?
Depolarisation and increased AP’s in vestibular nerve
What happens if cillia is distorted away from the kinocillium?
Hyper-polarisation and decreased discharge of APs in vestibular nerve
Why are all cupula angled differently ?
The pattern of firing and inhibition received to each cupula allows the brain to determine the body’s position in time and space
What is the sensory apparatus of the utricle and saccule ?
Maculae
On which plane do macula lie in the utricle?
Horizontal place
On which plane do macula lie in the saccule?
Vertical plane
How is cilia arranged within the maculae?
One kinocillium and a series of sternocilium which protrude into the otolith membrane
What is embedded within the otolith membrane?
Otoliths, CaCO3 crystals
Where do projections from vestibular nuclei on one side project?
Ipsilaterally, bilatterally and contralaterally to descending motor pathways
Where do vestibular nuclei receive input from?
Proprioceptors signalling limb and body position and from neck/eye muscles
Kinaethesia is achieved by what?
Vestibular nuclei projecting via the thalamus to the cerebral cortex which results in perception of movement and body position
What are tonic labyrinthe reflexes?
A primitive reflex which keeps the axis of the head in a constant relationship with the rest of the body
What are dynamic righting reflexes?
A reflex which corrects the orientation of the body when it is taken out of the normal upright position. Stops you falling when you trip
What is the static reflex?
When you tilt your head, eyes extort/intort to compensate so the image will stay the right way up
Describe dynamic vestibular nystagmus
A series of saccadic eye movements that rotate eye against direction of rotation of head and body so direction is gaze is preserved
When are you most likely to get symptoms of motion sickness?
When visual and vestibular inputs to the cerebellum are in conflict
What happens when there is acute interference with normal vestibular function as a result of infection?
Vertigo
What is menieres disease?
Vertigo, nausea, nystagmus and tinnitus due to over production of endolymph
