auditory system- CN VIII- finished

hearing is mediated by

the cochlear part of the vestibulocochlear nerve (8)

which part of the ear has both auditory and vestibular functions

inner ear

the outer is

auricle, external auditory meatus (canal), tympanic membrane

function is to conduct/propagate sound waves onto tympanic membrane

the middle ear is the

the malleus (hammer) , incus (anvil), and stapes (stirrup) these are called ossicles (tiny bones)

middle ear is an small air filled cavity within temporal bone

1. conduct sound from outer ear to inner ear via bony bridge

2. protect inner ear via acoustic reflexes : tensor tympani (5) attached malleus by the tympanic membrane, adn stapedius attached to stapes (7)

3. permit equalization of air pressure- opening of eustachian tube to prevent rupture of tympanic membrane, allows the air to leave middle ear and enter the throat

how does the Eustachian tube change if its a kid

more narrow and more horizontal on kid, so more ear infections

which ossicle is attached to the oval window

stapes

tensor tympani muscle job, activated by

tense eardrum by stabilizing malleus , by CN 5

internal body sounds or loud sounds- chewing, speaking, swallowing

stapedius muscles job

dampen sound by reducing stapes motion (7)
sudden loud external noises , like loud clap, firework, door slam

the structures of the inner ear

cohlea- auditory portion, snail shell, receives vibrations through oval window, sets perilymoh in motion to activate hair cells, and the vibrates dissipate against round window of the middle ear

vestibular apparatus- vestibule iwth utricle and saccule and 3 semicircular canals

oval window function

recives vibration from stapes, results in perilymph movements

round window function

dissipates the perilympathic vibrations out of the labyrinth; located inferior to oval window

internal chmabers of the cochlea include

organ of corti and basilar membrane

the organ of corti sits right above the basilar membrane

the organ of corti

are auditory receptors that transduce mechanical sound waves to electrical potentials

perilymph in cochlea will activate hair cells lining the basal membrane in the floor of cochlear ducts

how sound waves is turned into neural signal

1. sound waves enter ear drum

2. ossciles will vibrate and will move membrane of upper chamber (oval window).

3. the movement will cause perilymph (fluid in upper chamber) to move

4. vibration of basilar membrane and hair cells (in the cochlea)

5. hairs will bend in tectorial membrane and will depolarize

6. go to cochlear nerve endings are activated

what part of the basilar membrane is narrow and stiff? what sound will it transmit

base (near middle ear/round window), higher pitched sounds (whistle)/higher frequency by shorter fibers

what part of the basilar membrane is wide and flexible ? what sounds will it transmit

apex (free end), longer inner hair fibers by the apex will vibrate at lower frequency and produce low pitched sounds like drumbeat

low =long

pitch=

wave frequency measured in hertz

number of cycles per second

volume=

wave amplitude

measure in decibels

mediated by tensor tympani and stapedius

scala media is called

cochlear duct , filled with endolymph and contains organ of corti

what are the auditory functions with the CNS

1. orient head and eyes toward sound- travels via MLF inferior colliculus, superior colliculus, and cranial 11 nucleus

2. increase brain activity

3. provide conscious awareness of sound

what localizes sounds

inferior colliculus

what elicits eye movements towards sound

superior colliculus

what elicits head movement towards sound

CN 11 nucleus

what causes sleep arousal from noise

reticular formation

where does sounds applies meaning

secondary auditory cortex B 42- integration and recognition of sound

bilateral hearing is from crossing from multiple sites including

trapezoid- crossing between cochlear nuclei

superior olivary nuclei

lateral lemniscus

inferior colliculi

which cortex provides consciousness awareness of sound intensity and pitch, sound localization

B41- primary auditory cortex

what does the left auditory association cortex specialize in

lang processing, injury will cause auditory agnosia (not understanding speech)

what does the right auditory association cortex specialize in

interpreting environmental and non-lang sounds, injury will cause misinterpretation of environmental sounds

damage between external ear and middle ear causes

unilateral hearing loss

can be EAM, middle, cochlea, CN VIII, or into cochlear nuclei

symptoms of tinnitus and unsteadiness

due to bilateral innervation because of crossing sites, will not cause by lesion proximal or above cochlear nuclei

disease of external (eardrum) or middle ear (ossicles) is

conductive hearing loss- vibrations not transmitted from eardrum to oval window due to stiffen connections between middle ear bones

abnormal external auditory canal (cerumen)

middle ear (tympanic membrane rupture, otitis, ossicle sclerosis)

disease of inner ear (organ of corti or cochlear VIII n) or CNS auditory pathway

sensorineural hearing loss

causes can be loud noises, meningitis, ototoxic drugs, head trauma, viral infections, aging, cerebellopontine angle tumors (acoustic neuroma), internal auditory artery infract (rare)

cisplation- anticancer - cochleaotaxtic

gentamicin- antibiotic with ototoxic

tinnitus

hearing, constant, steady high pitche hum, ringing, buzzing, roaring

caused by presbycusis, otosclerosis, chronic otitis

presbycusis

hearing loss caused by gradual sensorineural loss due to age, nerve degeneration in inner ear or auditory/cochlear n

otosclerosis

hardening of bony tissue in ear labyrinth, forms around oval window and ankyloses stapes

otitis media

serous= noninfectious inflammation of middle ear with serum acculumation

suppurative- infectious bacterial inflammation of middle ear with pus formation

audiometry

functional hearing test

auditory evoked potentials

recordings of electrical potentials following specific auditory stimuli

weber test is for

sound lateralization for auditory acuity

useful to see if hearing loss in one ear is conductive or sensorineural

should hear equally on both sides

conductive will hear louder on affected side - because of reduced air conduction

sensorineural loss- tone is quieter on affected side

WEBER alone will not determine type of loss only where it lateralizes

rinne test

compares air and bone conduction- to differentiate conductive from sensorineural hearing loss

uses 512 tuning fork for best results

mastoid bone for BC

close to ear canal for AC

normal AC> BC 2:1

conductive BC>AC

sensorineural AC> BC in both ears but is decreased on affected side so less than 2:1

if you have conduction deafness what would you find with weber and rinne

weber- will be louder on affected side

rinne- BC>AC

otitis media, otosclerosis

what will you find with weber and rinne if nerve deaf

weber: sound will be lateralize to normal ear so louder in good ear , quieter

rinne- AC>BC but less than 2:1

aging drugs tumor