Vestibular function Flashcards
what is the vestibular system
sensory system essential in the control of posture and balance
what is the vestibular system and where is it found
inner ear - series of fluid filled membraneous tubes (labyrinths) that are embedded in the temporal bone
what are the components of the vestibular apparatus
3 semi-circualr canals - at right angles to each other
utricle
saccule
all contain sensory hair cells
what are the otolith organs
the utricle and saccule collectively
what do the otolith organs detect
Both:
linear accelleration
encode info about the position of the head in space
utricle - back/front head tilt
saccule - vertical movement
what do the semicircular canals (SSC)
detect rotational acceleration
what is the structure of the SSC
filled with endolymph fluid - contain sensory cells in swellings (cristae) at the base (ampulla) of the bony canals
what is contained in the cristae
flexible gelatinous structure called the cupula - stretches across entrire width of the ampulla
what does the cupula respond to
movement of endolymph fluid within the canals
what are found in the base of the cupula
cilia of hair cells that synapse with the sensory neurones of the vestibular nerve
how do the SSC canals detect rotational acceleration
- skull rotated right or left
- ampulla moves as it is embedded in the skull
- BUT endolymph does not move at first (inertia)
- inertia produces drag which bends the cupula and and ciliary in it in the opposite direction
- constant velocity - endolymph catches up and rotates at same speed - cupula and ciliary no longer bending
sudden stop:
- causes endolymph to carry on moving in same direction
- drag of cupula in opposite direction
- creates continuing sense of movement and dizziness
what are the two types of cilia of the hair cells
single large kinocilium
progressively smaller stereocilia
how does movement of the cilia allow the brain to determine its position in time and scape
movement of the cilia in different directions causes depolarisation or hyperpolarisation of the vestibular nerve
all cupula orientated slightly differently so the brain can build up a 3D image of body position form pattern of firing and inhibition
what happens when the cilia distort TOWARDS the kinocilium
DEPOLARISATION
increases discharge of APs in the vestibular nerve
what happens when the cilia distort AWAY from the kinocilium
HYPERPOLARISATION
decreased discharge of APs in the vestibular nerve
where does integration of this sensory information from the cilia and vestibular nerve take place
cerebellum
what are the sensory apparatus of the saccule and utricle known as
maculae
how are macula orientated
utricle - horizontal plane
saccule - vertical plane
what is the structure of the maculae
set of cilia (single kinocilium, series of stereo cilium) protrude into otolith membrane
crystals called otoliths are embedded on other side of the membrane
what detects tilting of the head
macula in the utricle (horizontal plane)
otoliths have greater density than endolymph - more affected by gravity - otoliths moving move membrane - membrane moving moves cilia
how is a backwards tilt detected
moves otoliths TOWARDS kinocilium
depolarisation and increased APs in vestibular nerve
how is a forward tilt detected
moves otoliths AWAY from kinocilium
hyperpolarisation and decreased APs in vestibular nerve
what detects vertical forces (e.g. movement in a lift)
macula in saccule
also provide info on orientation of the head when lying down
where do projections from the vestibular nuclei project
ipsilaterally, bilaterally and contra-laterally to descending motor pathways
also extraocular nuclei (extraocular muscles)
