vestibular system Flashcards
main functions of vestibular system
which way is up
where you are moving
keep eyes still as you move
maintain upright posture
perception of own movement within space
anatomy of vestibular system - 2 main components and their sub sections
otolith organs:
linear motion
- utricle = left/right and back/forwards
- saccule = up/down
semi-circular canals:
head rotation
- anterior vertical
- posterior vertical
- horizontal = less complex movements, spinning round
all canals contain endolymph
end of each canal is in ampulla - connect to hair cells
types of fluid in vestibular system
endolymph = through centre of canals = high K+
perilymph = surrounds canals = normal body fluid, high Na+, low K+
vestibular hair cells - function
stereocilia
non-selective cation channel opens when hairs are moved due to higher frequency - depolarisation
channels shut as hairs move the other way - hyperpolarisation
0-20Hz - much smaller movements than auditory system
vestibular hair cells arrangement vs cochlear
cochlear IHCs are sensitive to higher frequencies - more spread out, less restricted, in rows
vestibular SHCs - more rigid as a structure in a bundle - more circular shaped bundle
vestibular vs cochlear hair cells (individual cells)
stereocilia aren’t true cilia - not microtubule
vestibular = keep kinocilium (a true cilia cell) throughout life
cochlear = planar cell parity (tall to short cells)
2 types of vestibular hair cell
type 1 = one afferent dendrite surrounds whole base of hair cell - calyx shape
type 2 = vesicles released onto afferent dendrite - normal synapse
head tilt and linear movement mechanism
same hair cells for both of these functions
saccule and utricles are involved
macula = sensory patch where hair cells are found
striola = line running through utricle - hair bundles organised differently either side (mirrored)
— move one way = half of the hair cells are excited and the other half on the other side of striola are inhibited
hair bundles project into otolithic membrane (gelatinous)
otoconia = gives weight to membrane so when head is moved down, gravity pulls the otoconia down and therefore the membrane too - moving the hair bundles with it
ambiguity of vestibular input to CNS
same hair cells moved in same direction with head tilt and sideways movement
CNS only knows action potentials, not how cells are activated
other systems work together to resolve this:
visual = interpret the feeling
muscles = feel your neck muscles tilting or your legs stepping to the side
head rotation mechanism
hair cells in horizontal semi-circular canal stick up into cupula (vertical jelly-like substance)
endolymph moves more slowly than solid bone structures so as head rotates, endolymph pushes the other direction, causing cupula to bend
as cupula bends, hair cells are moved and ion channels open so sensory fibres are depolarised and fire action potential
hair cells are oriented so short hairs face the front and endolymph moves the same direction around the whole circle so when one side is excited, the other is inhibited
vestibular nerve - central pathways to other brain areas (4)
cerebral cortex = perception of what is happening
reticular formation = visceral response e.g. feel sick on a rollercoaster
oculomotor nuclei = input into muscles to control eyes - correct for whatever movement has occurred
cerebellum and spinal cord = maintain posture
vestibulo-ocular reflex
demonstrated by shaking head vs paper - easier when shaking head as vestibular system is fast working, visual system uses G-protein coupled receptors and so is slower
turn head right = eyes are pulled back left
continual spinning round = vestibular nystagmus - resetting of eye position
— slow phase = eyes rotate opposite to head movement
— quick phase = rapid resetting movement back to centre of gaze
