L19: The ear and hearing Flashcards
frequency=
number of waves per second
what is the human frequency range
20-20,000
what is intensity
amplitude of the pressure change
which part of the temporal bone is the ear in
petrous part
3 parts of the outer ear
- pinna
- external auditory meatus
- Tympanum
functions of pinna (3)
- funnels sound into ear canal
- aids in the vertical localisation of sounds
- filters sound
how long and wide is the external auditory meatus
7mm in diameter, 25mm long
where does the external auditory meatus run from
auricle to tympanum
what surrounds the first 1/3 of the external auditory meatus
cartilage
what surrounds the last 2/3 of the external auditory meatus
bone
function of external auditory meatus
- focuses sound energy on eardrum
- amplifies sound corresponding to frequencies of human speech
what shape is the tympanic membrane externally
concave
most depressed part of the eardrum=
umbo
what bone is attached to the medial tympanic surface
malleus
function of tympanic membrane
vibrates in response to sound pressure to transmit sound energy
3 ossicles in the middle ear
malleus, incus, stapes
function of the middle ear
converts kinetic energy to hydraulic energy in inner ear
where does the stapes sit
in the olave window
what is the eustachian tube
connects middle ear cavity to nasopharynx
when does the eustachian tube open
lowering and protruding the lower jaw
function of the eustachian tube
allows pressure equalisation between middle ear and external ear, preventing damage to the tympanic membrane
2 muscles of the middle ear
- tegmen tympani
- stapedius
what does tegmen tympani attach to
malleus
what does the stapedius attach to
stapes
what does contraction of the middle ear muscles do
reduces ability of the ossicles to vibrate and so dampens sound reaching inner ear
acoustic reflex =
muscles in the ear contracting in response to high intensity sounds
when in stapedius activated
during speaking
when is tegmen tympani activated
during chewing
which nerve gives of 2 branches that enter the middle ear cavity
the facial nerve (gives off chorda tympani and stapedial nerve)
which nerve runs anteriorly across the pars flaccida of tympanic membrane
the chorda tympani
what does the chorda tympani innervate
taste buds of 2/3 anterior tongue
what does the stapedial nerve innervate
stapedius muscle
what innervates the tegmen tympani
mandibular part of trigeminal nerve
where do bones of the skull transmit sound to
the inner ear
what frequencies do bones transmit
lower frequencies
how does your own voice sound different
it sounds lower to yourself than it is
function of the cochlea
uses movement of fluid to sense external pressure changes (sound)
2 parts of the labyrinth of the inner ear
- bony labyrinth
- membranous labyrinth
what is the membranous labyrinth
system of tubes and chambers within bony labyrinth filled with endolymph
endolymph is high in which ion
Na+
what separates bony and membranous labyrinth
perilymph
which is the only area in which membranous labyrinth doesn’t conform to shape of bony part
vestibular region
what is the cochlea
is a coil which makes 2 and 3/4 turns around a bony column
3 sections of the cochlea
- scala media
- scala vestibuli (above)
- scala tympani(below)
what is scala media filled with
endolymph
what is scala vestibule and scala tympani filled with
perilymph
what separates scala vestibule and scala media
reissner’s membrane
what separates scala tympani and scala media
basilar membrane
what sensory epithelium is on the basilar membrane
organ of corti
route of pressure wave travel in the cochlea
vibrations in the oval window–> along the scala vestibuli in perilymph and back along scala tympani to round window
what does pressure wave travel in the perilymph cause
displacement of the basilar membrane and vibrations of organ of corti
what determines when the pressure waves cross the basilar membrane
frequency of the sound
where is the basilar membrane most stiff
nearest to base of cochlea
which frequencies can cross the basilar membrane at the base
high frequencies
what is tonotopy
low pitches sounds at apex and high pitched sounds base
what does the organ of corti do
transduces pressure waves into action potentials
what is contained within the organ of corti
auditory receptors with there own hair cells
what do outer hair cells do
amplify mechanical input to inner hair cells
what do inner hair cells do
send information to brain stem via spiral ganglion and CN8
what can happen to hair cells with excessively loud noise
irreversible hair cell damage
feature of noise induced hearing loss
can be very specific (a few frequencies)
auditory pathway mnemonic
SLIM
- Superior olivary complex
- lateral lemniscus
- inferior colliculus
- medial geniculate nucleus
where is the auditory cortex located
temporal
where does partial decussation in the auditory pathway happen
between cochlear nuclei and superior olivary complex
what does decussation allow
inputs from left and right ears to be compared in superior olivary nuclei (SON)
what does medial SON do
detects differences in the time sounds reach each ear
what does lateral SON do
detects differences in sound intensity reaching each ear
how is high frequency localised
difference in sound intensity (lateral SON)
how is low frequency localised
time differences in each ear (Medial SON)
2 type of hearing loss
conductive
sensorineural
common causes of conductive (5)
- earwax
- otitis externa
- perforated ear drum
- membrane tension
- otitis media
conductive hearing loss=
problem conducting sound waves through outer ear, eardrum or middle ear
sensorineural hearing loss=
problem in cochlea, vestibulocochlear nerve, auditory cortex of brain
5 common causes of sensorineural
- congenital
- measles, Mumps, meningitis, syphilis
- noise induced
- trauma
- ototoxic drugs
2 hearing tests
rinne
weber
what does rinne test measure
relative conduction of sound through air and bone
how to perform rinne test
vibrate tunning fork over auditory canal and then against mastoid process
what is normal rinne test result
AC>BC
conduction hearing loss rinne test=
BC> AC
sensorineural hearing loss=
AC>BC (normal)
-bone and air conduction affected equally
how to perform webers test
tunning fork held middle of forehead, patient reports which ear hears sound loudest
AC>BC and weber lateralizes left=
sensorineural loss in right
AC>BC and webers lateralizes right=
sensorineural loss in left
in right ear conductive hearing loss which side will webers lateralise to
right (as there is less sound traveling through middle ear so bone conduction sounds louder)
