semicircular canals
angular/rotational movement
saccule and utricle
linear acceleration - translational motion and gravity
stereocilia and kinocilium
- resting - cells slightly depolarized releasing small NT
- fluid flow can lead to depolarization (more NT) or hyperpolarization (less NT)
- push toward kinocilium –> K+ influx –> more depolarization and AP –> more glutamate/aspartate release and vice versa
- push away from kinocilium –> close K+ channel –> hyperpolarization –> less NT
stimulation of crista ampullaris in semicircular canals
fluid moves cupulla –> move cilia
- move membranous and bony labyrinth –> fluid stagnant –> stimulate cupulla
- stop movement –> fluid keeps going –> stimulate cupulla
semicircular canal muscles
- horizontal - lateral and medial recti
- LARP - left vertical recti, right oblique
- RALP - right vertical recti, left oblique
rotation of head vs. eye movement
- head rotates toward the stimulated vestibular apparatus –> eyes pull in opposite direction to maintain focus
- stimulus from eye is SLOWER than that from vestibule
macula
otolith organ in saccule and utricle - contain otoconia
- cilia in both directions –> depolarization both ways
- utricle –> detect horizontal acceleration
- saccule –> detect vertical acceleration and gravity
vestibulo-ocular reflex
turn head and eyes remain fixed in opposite direction - maintains focus
-ex. read when moving head
vestibulo-collic reflex
head and neck stay on track when body is moving
-ex. chicken
vestibulo-spinal reflex
adjust posture when changing positions
lateral vestibulospinal tract
IPSILATERAL, maintain posture of lower body/limb
- excitatory signals to ventral horn & muscles
- rigidity (hypertonic) if there is lesion of cerebral cortex –> no inhibitory stimulus
medial vestibulospinal tract
mostly ipsilateral, some fibers cross
- keep head posture still in space
- vestibulo-cholic reflex
vestibulo-ocular reflex (VOR)
keep eyes still while head rotates
- brain adjusts to eliminate retinal slip
- virtual reality - brain thinks you are moving, but are not
optokinetic signal
eye stimulus influences vestibular apparatus
- rotate in dark –> response dies sooner
- rotate in light –> longer response bc have eye stimulation
visual vestibular conflict
virtual reality for ex. - brain making you think you have stimulus from vestibular apparatus –> motion sickness
-occurs from vestibular and visual systems being unequal
vertigo and nystagmus
vertigo - out of balance; head motion when head is still
nystagmus - associated with tinnitus
-vision stimulus lead to vomiting
peripheral vestibular dysfunction
- head tilt, functional imbalance, difficult path integration
- causes: benign positional vertigo (dislodged otoconia), viral, alcohol, menier’s (endolymph pressure), toxins
