vestibular system Flashcards
- Recognize and name the components of the vestibular system.
3 semicircular canals (superior, inferior and horizontal), utricle and saccule. Perilymph surrounds the semicircular canals, and they are filled with endolymph. Stria vascularis of cochlear duct has air to stabilize pressure
- Describe the hair cell and its physiology.
kinocilium is the tallest stereocilia. Stereocilia are mechanical transducer
Function of vestibular system
motion detection (self and surroundings) and orientation (body vs gravity, limb vs body)
what structure senses gravity
the maculae on the utricle or saccule- macula are covered with otoconia/otoliths (calcium crystals) which are very sticky so they stick. They can fall off and accumulate in lowest part of ear, becoming bigger. Once the clump becomes too big it becomes benign paroxysmal vertigo.
motions sensed by utricle
– Horizontal orientation – Side to side tilt or front to back rocking – Forward acceleration in a car
motions sensed by saccule
– Vertical orientation – Elevator sensations, bouncing – Falling sensations
what happens when you lie down in the maculae
role reversal- utricle detects verticle orientation, saccule detects horizontal
structure of maculae
otoliths on surface, then sensory hair cells and supporting cells, then nerve fibers, then temporal bone
What is the ampulla
a dilation near the semi circular canals that has endolymph inside it, but the crista with the cupula on top blocks that fluid flow and detects movement
motion sensed by cupula
acceleration, deceleration, does not sense continued motion
how do we distinguish right hand from left hand turn
the semicircular canals are positioned at a 45 degree angle and mirror each other btw the two ears (so the ampulla is always at the top. At rest, there is equal firing from the right and left ear. When you turn to the right, the fluid in the canal moves towards the ampulla on the right, and away from the ampulla on the left. so the right semicircular canal “turns on” and increases electrical signals while the left “turns off” and decreases electrical signals
vestibular nerve anatomy
superior branch innervates anterior and horizontal semicircular canals, utricle and small part of saccule. Inferior division innervates posterior semicircular canal and saccule
vestibulo-ocular reflex
neuron from hair cell (with cell body in scarpas ganglion) synapses at vestibular nucleus, secondary neuron synapses with oculomotor nucleus, then goes to the eye to control eye movements. This is a 3 nerve reflex, shortest reflex in body. This keeps eyes steady during head movement.
vestibulo-colic reflex
keeps head stable and level with bodily movement. Controlled by motor neurons in the upper spinal cord. Damage to this pathway causes the head to fall off to one side.
vestibulo spinal refelx
automatic righting reflexes to prevent falls during head and body motion. Keeps person stable and upright when sitting and standing. Controlled by motor neurons in lower spinal cord.
