Special senses III: vestibular system Flashcards
vestibular apparatus: features
- inner ear also has structures for self motion -> vestibular labyrinth
- sensory receptors (hair cells) in labyrinth function as acceleration detectors
vestibular apparatus: 2 structures for different motions
semicircular canals:
- detect rotational acceleration (turning head, nodding)
otolith organs:
- linear (straight line) acceleration, force of gravity
vestibular hair cells: differs from auditory
- possess true cilium (kinocilium) like longer stereocilium
- relative orientation of stereocilia and kinocilium: polarity of hair cells, confers directional sensitivity
hyperpolarisation
vestibular hair cells: - bending stereocilia towards kinocilium causes
- bending stereocilia towards kinocilium causes depolarisation,
vestibular hair cells: - bending stereocilia away from kinocilium causes
hyperpolarisation
dynamic (kinetic) labyrinth: semicircular canals features
- transduce rotational acceleration
- oriented perpendicular to each other, code acceleration in 3 directions
- sensory end organ (crista ampullaris) located in ampulla at bae of each canal
dynamic (kinetic) labyrinth: semicircular canals name canals
- ant
- lateral
- post
dynamic (kinetic) labyrinth: semicircular canals- ant
- up down motion
- yes nod
dynamic (kinetic) labyrinth: semicircular canals- lateral
- side to side motion
- no shake
dynamic (kinetic) labyrinth: semicircular canals- post
- rocking motion
- ear to shoulder
crista ampullaris: features
- each have several hair cells
- hair cell’s stereocilia (40-70/ cell) project into membrane bound gelatinous mass= cupula
- hair bundles polarised in same direction- directionality provided by canal shape
- hair cells synapse onto 1˚ vestibular sensory afferents that travel to brain via CN VIII
semicircular canals: response to rotational motion
- rotation of head rotates canal
- endolymph lag behind and exerts force on cupula
- pressure on cupula bends stereocilia in opposite direction to head
- bending towards kinocilium - depolarisation of hair cell (MET channels, same as auditory system in cochlea)
- increase NT onto 1˚ afferent neuron -> increased spiking
static labyrinth- otolith organs: features
- utricle and saccule are bulges in labyrinth located btw semicircular canals and cochlea
- each have patch of sensory cells= macula
static labyrinth- otolith organs: moving head
- hair cell cilia embedded in gelatinous matrix
- matrix have small crystals of Ca carbonated = otoliths
- otoliths add mass
- head moves -> matrix lags behind and bend stereocilia
static labyrinth- otolith organs: direction sensitivity
- hair cells in different zones of macula of utricle and saccule are oriented in opp directions:
static labyrinth- otolith organs: saccule direction
- kinocilium away from striola
- hair cells detect up and down linear acceleration (going up in lift)
static labyrinth- otolith organs: utricle direction
- kinocilium towards striola
- hair cells detect forward and backwards (walking forwards, nodding head)
neural pathways for vestibular info:
- vestibular (bipolar) neurons supply all 5 vestibular organs
- afferent fibres project via vestibular n (vestibular branch of CN VIII)
- synapse in vestibular nuclei (brainstem), heavily influenced by flocculonodular lobe of cerebellum
functional role of dynamic labyrinth (semicircular canals): VOR
- vestibuloocular reflex (VOR)- fastest reflexes in body
- compensatory movements of eyes, keep visual gaze on target during rotational movements of head, stabilises image on retina (prevents blur)
- doesn’t need visual input
- proprioceptive info (from muscle spindles in deep mm around cervical vertebrae) relayed to cerebellum via spinocerebellar tracts
functional role of dynamic labyrinth (semicircular canals): vestibular nuclei receive input from
- flocculonodular lobe of cerebellum
- semicircular canals
functional role of dynamic labyrinth (semicircular canals): vestibular nuclei neurons
- project into cranial n inn extraocular mm of eye (CN III, IV, VI)
- mm contract to move eyes in opp direction to head movement
- [caloric test for brain function]
functional role of static labyrinth (otolith organs): VSR
- vestibulospinal reflex (VSR) v fast reflex
- controls balance, coordinated head/ neck movements w those of trunk/ limbs (stationary, walking)
functional role of static labyrinth (otolith organs): project into
- vestibular nuclei (receive input from cerebellum, visual system, proprioceptors)
functional role of static labyrinth (otolith organs): neurons in vestibular nuclei project into
- spinal cord
- via lateral vestibulospinal tract
functional role of static labyrinth (otolith organs): features
- increases tone in antigravity (extensor mm) in trunk, limbs on the side which head is tilted
- works in concert w proprioceptors and retina to maintain upright posture, keep head upright
functional role of static labyrinth (otolith organs): absence of vision,
- fall likely if either vestibular/ conscious proprioceptive system has been compromised (Romberg’s sign)
vestibular cortex: features
- parietoinsular vestibular cortex (PIVC) and adjacent region of sup temporal gyrus
- spatial orientation, conscious awareness of self motion and equilibrium
- more multimodal association area than true unimodal 1˚ sensory cortex
- integrates vestibular, visual, somatosensory (proprioceptive) info
- modulate brainstem vestibular function via descending fibres
