Auditory and Vestibular Systems Flashcards
what is responsible for receiving afferent info for both auditory and vestibular systems?
CN VIII
bony labyrinth (parts and location)
cochlea, vestibule, semicircular canals
located in petrous part of temporal bone
membraneous labyrinth
cochlear duct, utricle and saccule (vestibule), semicircular ducts
perilymph
fills perilymphatic space (between bony and mem labyrinths), similar to extracellular fluid, continuous with subarachnoid space
endolymph
fills mem labyrinth, continuous, closed system, similar to intracellular fluid, cells in walls of mom labyrinth are connected with tight jnctns allowing diffusion
- secreted by cells in cochlea called stria vascularis
- reasorbed in endolymphatic sac
hair cells
- auditory and vestibular receptors
- within mem labyrinth, sit on basilar mem
- stereocilia project into endolymph (apical projectinos)
- basal projections synapse with CN VIII
- sterreocilia arranged in rows (tallest = kinocilium, ONLY IN VESTIBULAR PORTIONS)
what are the barriers btwn endolymph and perilymph
tight junctions btwn hair cells
what type of channels do hair cells make
mechanosensitive transduction channels
- rigid bc actin, bend at base
- deflect toward tallest stereocilia=depolarize cell
- deflect away from stereocilia=hyperpolarize cell
- arrangement is key to type of signal getting transduced (sound, head movement, head position)
cochlear division
- convey info about sound
- organ of corti (auditory receptor organ)
- outer and middle ear (air filled)
- inner ear (liquid filled)
cochlea
membrane suspended in perilymph and filled with endolymph
-bone, forms 2 3/4 turns, modiolus with osseous spiral lamina
sound travel path in cochlear division
vestibule->oval window->scala vestibule->helicotrema->scala tympani->round window membrane
fnctn of cochlear system
-traveling waves in the basilar mem stim hair cells in the organ of corti, in locations that depend on sound frequency
- intensity: (loud), rate and number of nerve firings
- frequency: (pitch), basilar membrane and organ of corti
- location: compare stim btwn ears within CNS
organ of corti
- hair cells sit on basilar mem, outer hair cells in tectorial mem
- basilar mem: stiff at base (responds to high frequency), floppy at apex (low freq)
when can cochlear implants be used
when hair cells are damaged but CN VIII endings are intact
ascending auditory information
- primary afferents stimulated by hair cells have cell bodies in spiral gang and synapse at 1. dorsal cochlear nuc, and 2. ventral cochlear nuc (both project bilaterally)
- lat lemniscus terminates at inf colliculus, then sends fibers thru inf brachium to med geniculate nuc (MGN( of thalamus, which projects to transverse temporal gyri (primary auditory cortex) on sup aspect of temp lobe
where do 2nd order fibers from dorsal cochlear nuc ascend
in lateral lemniscus
where do 2nd order fibers from ventral cochlear nuc synapse
superior olivary gang (involved in sound localization) by crossing thru trapezoid body, then ascend thru lat lemniscus
vestibular divisions fnctns
regulate posture, coordinate eye and head movement
components of vestibular divisions
bony part: vestibule, 3 semicirc canala
mem part: otolithic organs (saccule and utricle), 3 semicirc ducts
dilated part of semicirc duct
ampulla, contains
- crista: supporting and hair cells
- cupula (gelatinous mass): responds to angular acceleration
otolithic organs
- have tuft of hair cells called macula
- stereocilia project into gelatinous mass (otolithic mem)
- utricle sensitive to: forward/back, side/side
- saccule sensitive to: forward/back, up/down
- contain otoconia (calcium carbonate crystals)
primary afferents of vestibular division
- hair cells stim the peripheral process of vestib division of CN VIII
- vestib gang projects directly to cerebellum and vestib nuclei (1. inf, 2. med, 3. lat, 4. sup)
projections into vestib nuclei
- cerebellum: directly from flocculonodular lobe
- SC: directly from spinovestibular fibers
- visual info: indirect from various nuclei in BS (to distinguish btwn movement across retina and just movement)
- contralat vestib nuc: extensively interconnected
projections out of vestib nuclei
- cerebellum: coordinated head movements
- SC: regulate posture (via lateral vestibulospinal tract)
- nuc of CN III, IV, VI: coordinate eye movements (via vestibuloocular reflex)
- thalamus->cerebral cortex: conscious awareness
- visc nuc: autonomic effects
lateral vestibulospinal tract
- stabilize posture
- lat vestib nuc->runs to STT->antigravity mm at all spinal levels
- stays ipsilateral
med vestbulospinal tract
- stabilize head
- med vest nuc->MLF->cerv spinal cord
- bilateral
vestibuloocular reflex
- generate eye movements that compensate for head movements
- afferent limb: CN VIII
- efferent limb: nuc that control exraocular mm
- interneuronal connections: MLF and RF
nystagmus
eye shakes back and forth
-physiological and pathological
position sense
- vestibular sense
- proprioceptive sense
- visual sense
need 2/3 to fnctn normally
