week 16: Motor Systems L4 Flashcards
Balance and Posture Vestibulo-ocular reflex
what is the stability of an object based on
centre of mass
support area
where does vestibular apparats sit
inner ear, hair cell
function of vestibular apparatus
detects head motion and position relative to gravity
two main components of vestibular apparatus:
semi-circular canals: detect angular velocity (rotational movement)
otolith organs: detect linear acceleration and angular position relative to gravity
how does vestibular apparatus pick up changes in 3 directions
it has 3 canal rings: anterior, posterior, horizontal
how do hair cells function in the semi-circular canals?
hair cells in the ampulla are embedded in the cupula, displaced by by endolymph movement
what are the two otolith organs and what do they detect
utricle: detects horizontal acceleration
saccule: detects verticle acceleration
how do otolith organs detect acceleration
each contains a macula (pad of hair cells) that detect orientation of head relative to gravity
what are the canals filled with
endolymph
how are signals from semi-circular canals processed?
each has antagonist canal pairs on opposite side of head
allow for comparison between two sides based on differences in nerve firing rate
what happens to the fluid in the semi-circular canal when you move head
fluid within cupula moves in opposite direction of the head movement, causes hair cells to deviate in the opposite direction
how does brain receive info about head movement
hair cells send spike signlas to vestibular nuclei on both sides of the brain allowing brain to determine if balance is being maintained
how does the vestibular sytem function as a binary system
operacts with high activity or low activity
what happens if one side of the vestibular system is lost?
biased system occurs, leading to loss of balance due to asymmetric signalling
what is the eyes not moving despite the head moving a feature of?
vestibulo-ocular reflex
what is the VOR
reflec that tabilises vision by keeping the yes fixed on an object while the head moves
how does the VOR function in head movement?
head moves, vestibular system activated, eyes move in the opposite direction
what structures detect the head movement that triggers VOR
semicircular canals and otolith organs
where does the vestibular info travel to control eye movement?
vestibular nerve sends signals to oculomotor, trochlear and abducens nuclei which controls the extraocular muscles
example of what happens when the head turns right
right vestibular nucleus activated
left vestinular nucleus inhibited
eyes move to the left to compensate
role of VOR when head is at rest?
keeps vision stable, eyes remain steady
what happens if VOR is not working properly
image slips across the retina during head movement causing blurred vision and nystagmus
what happens if one vestibular organ is damaged
only one side sends signals, causing imbalance and nystagmus
brain misinterprets motion leading to dizziness and visual instability
what happens if both vestibular organs are damaged
brain cannot detect movement properly leadin to oscillopsia and severe balance problems
what causes motion sickness
sensory conflict occurs when the vestibular system detects motion but the visual field is stable (or vice versa)
what happens when there is a mismatch between eye movement and head movement?
cerebellum detects error and adjusts the reflex to improve accuracy
what brain structure helps calibrate the VOR
cerebellar flocculus
what inputs does the cerebellar flocculus receive?
mossy fibres
climbing fibres
how does the cerebellum adjust the VOR
Purkinje cells modify their output, sending new signlas to vestibular nuclei
alters the strength of the VOR
what are the two main control elements of postural stability
feedforward control (predicts and prepares for balance disturbances before they happen, based on past learning and experiences)
feedback control
(responds to the unexpected balance disturbances after they occur, uses sensory input for real time adjustements)
