PSL300H1 Study Guide - Final Guide: Semicircular Canals, Eustachian Tube, Membranous Labyrinth
ProfessorDoug Mac Kay
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ANATOMY OF THE EAR
EQUILIBRIUM → motion of head and tilt
sense of equilibrium detects motion of head and its tilt relative to gravity
get info abt these from many senses → proprioception and vision.
vestibular apparatus also know as membranous labyrinth
vestibular apparatus: set of fluid-filled chambers.
semicircular canals: cristae → sense rotational acceleration.
2 otolith organs: utricle and saccule, each have maculae which senses head's tilt and translational
acceleration (motion and relative position in space).
3 orthogonal canals for 3 dimensions of head rotation:
horizonal canal → senses side to side rotation (shaking head in "no" motion), superior and posterior →
sense up and down nodding eat-to-shoulder tilt. each canal filled with endolymph, ends in bulge
(ampulla), containing its crista.
crista contains mechanreceptors → hair cells , each have stereocilia in apical membrane. cilia extends
into cupula (gelatinous mass), seals off into canal. head turns → endolymph lags and pushes on cupula →
hairs bend (if head swings right, endolymph pushes hair to left). when hair cells move, either inhibited or
each vesitbular hair cell has on long stereocilium: the kinocilium. each hair cell has directionality bcs
oriented twrds the kinocillium. if hair bends twds kinocilium → hair cell depolarized → NT released →
sensory neuron activated. if they bend away → they hyperpolarize.
tiplinks: connect stereocilia. when they open up, ion channels open.
hair cells = tonically active. release NT onto primary sensory neurons.
lag of endolymph reflects change in head rotation: constant speed after 20 s→ no endolymph lag., cupula +
hairs return to rest position.
if head stop abruptly → fluid built up momentum and can't stop immediately → pushes cupula in opposite
in maculae→ hair cells extend stereocilia into gelationous otolith membrane. otoliths = calcium carbonate
and protein particles on membrane surface. gravity/acceleration moves otoliths, membrane moves with
them, hairs bend. when head upright, macula of utricle = horizontal, saccule = vertical.
equilibrium pathways project to cerebellum → mantain posture and sense of space and balance.
hair cells activate primary sensory neurons on vestibular nerve (CN VIII) → those neurons pass directly to
cerebellum or synapse in medulla, proceed to cerebellum or up through reticular formation and thalamus to
semicircular canals and head
otolith organs and tilt
utricle, saccule, maculae
posterior, horizontal and
external ear → pinna, ear canal, sealed by tympanic membrane
middle ear → air filled space connected to pharynx by Eustachian tube
inner ear → sensors: vestibular apparatus for equilibrium, cochlea for
EQUILIBRIUM AND HEARING
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