Chapter 15b Hearing and Equilibrium
Ear anatomy
•external earexternal acoustic canal tympanic membrane
•middle ear3 ossicles
•malleus
•incus
•stapes
•inner ear
–cochleahearing
–vestibule equilibrium
–semicircular canalsequilibrium
HEARING
cochlea anatomy
•cochlear ductfluid filled membrane
–fluidendolymph
–receptor Organ of Corti = spiral organ
•surrounded by 2 chambers :
–fluidperilymph
–scala vestibulicontacts oval window
–scala tympanicontact round window
Organ of Corti
•= spiral organreceptors for hearing
–within cochlear duct
•basilar membrane support
•hair cellsreceptor cells
–stereociliaextensions into tectorial membrane
•tectorial membranecovers stereocilia ; stationary
Sound
•= alternating zones of high and low pressure
•sound is a vibration
•waves of vibrating air (or any medium)
physics terms
•frequency # waves per second hertz (Hz)
•wavelengthdistance betw crests
•amplitudeheight of each wave
•pitch= frequency
–hertz (Hz) = cps
–20 to 20000 Hz
–most sensitive range
•1500 – 4000 Hz
•loudness= amplitude
–decibels (dB)
–0 to 120 dB
–0 = threshold
hearing
•GOAL = change sound into action potential depolarize the receptor cells
–open Na channels
•How?stretch their hair
transmission of sound / vibration
•sound wave (air) vibrates tympanic membrane
•3 ossicles amplify the vibration
•stapes vibrates the oval window
•oval window vibrates perilymph
•perilymph vibrates endolymph
•endolymph vibrates basilar membrane
•basilar membrane vibrates hair cells
excitation of receptor cells
•organ of Corti
•basilar membrane vibrates hair cells
•stereocilia stretch against tectorial membrane
•open K channels
•K+ (in endolymph) rushes into cell
•hair cells depolarize
•hair cells release NT
Pitch
•varied thickness of basilar membrane
•responds to different frequency
•frequency ~ pitch
•multiple pitches possible
•specific areas of auditory cortex
Pitch and auditory cortex
auditory processing
•pitcharea of basilar membrane / auditory cortex
•loudnessnumber of hair cells stimulated frequency of action potentials
•localizationwhere is sound coming from
–compares both ears
•intensity
•timing
auditory pathway
•to temporal lobe
–cochlear nerve
–spiral ganglion
–cochlear nuclei
–thalamus
–temporal lobe
•to inferior colliculi
–auditory reflex
•to cerebellum
problems
•deafness
–conduction deafness
–neural deafness
•tinnitus
•Meniere’s syndromehearing loss tinnitus vertigo
EQUILIBRIUM
equilibrium anatomy
•Vestibular apparatus = 2 structures :
•vestibulelinear equilibrium (static)
•semicircular canalsrotational equilibrium (dynamic)
receptors
•linear accelerationutricle saccule
–maculareceptor mechanism
–hair cellsreceptors
•rotational accelerationsemicircular ducts
–ampullareceptor mechanism
–hair cellsreceptors
macula anatomy
•receptor mechanism inutricle , saccule
•hair cells
•stereocilia
•kinocilium
•otoliths
excitation of macula
•position change moves otoliths-bends sterocilia
•toward kinociliumdepolarize
•away from kinociliumhyperpolarize
•opposite sides
ampulla anatomy
•receptor mechanism of semicircular ducts
•crista ampullaris
–hair cells
–cupula
excitation of ampulla
•rotation moves endolymph
•endolymph deforms cupula
•cupula bends sterocilia depolarize
equilibrium pathway
•hair cells
•vestibular nerve
•vestibular nucleimedulla
•cerebellumreflex movement
•cerebrumparietal lobe conscious awareness of position and movement
equilibrium reflexes
•sensory input from
–vestibular apparatus
–proprioception
–vision
•response
–eye movment
–skeletal muscleesp neck and torso
•vestibulospinal tract
•CN XI
problems
•vertigodizziness
•nystagmus
•motion sickness