outer ear is made up of 2 structures:
- pinna
2. external auditory meatus (ear canal)
concha
depression in lower center of the pinna
funnel like shape of the pinna gives rise to its basic function of…
collecting and sending sound waves through the ear canal
external auditory meatus (EAM)
- tube that runs from the pinna to the ear drum (tympanic membrane)
- lined with epithelium and tiny hairs (cilia)
- contains glands in the cartilaginous parts that produce earwax
EAM length
children = 6mm adults = 23-29mm
function of cerumen
-aids in keeping the ear canal moisturized and clean of debris that can accumulate
2 main functions of EAM
- protect the delicate middle and inner ear from foreign bodies that could damage these structures
- boosts amplitude of high frequency sounds
resonant frequency
or natural frequency
the frequency in which so meting responds or vibrates best to
when frequencies enter the EAM and are close to or at the resonant frequency of the EAM what happens?
they get an automatic boost of about 10-15 dB
the boost helps
higher frequency sounds
localization
tympanic membrane
anatomic boundary between outer and middle ear
TM is comprise of multiple layers:
epithelial, medial membranous, fibrous (in-between top 2)
TM medial layer
lined with mucous membrane
TM 2 main sections
- pars flaccida
- pars tens
pars flaccida
located superiorly
is flaccid
pars tens
larger section
more stiff
located inferiorly
ossicles
smallest bones in the body
- malleus
- incus
- stapes
all articulate with each other
suspended by ligaments that help it move
malleus
attaches with the TM
-TM vibrates from sound energy impinging on it and malleus moves at the same vibratory speed
incus
middle bone, less than 1cm
2 processes of incus
short crus
long crus
long crus
attached to head of stapes
short crus
fits into recess wall of TM
stapes
resembles stirrup
has 2 crura and a footplate
footplate function
helps push acoustic energy into the inner ear
fits into oval window
E- tube functions
- equalize air pressure between middle ear cavity and the nasopharynx
- help drain fluids that may accumulate in the middle ear
inner ear consists of
the auditory and vestibular labyrinth
-each has a osseous and membranous labyrinth
cochlea
snail shape part of osseous labyrinth
- HOUSED WITHIN THE TEMPORAL BONE
- straightened out is about 3.5 cm
- tonotopially organized
membranous labyrinth
goes inside osseous lab
auditory lab is referred to as the
cochlea and is the sensory organ of hearing
semicircular canals
sensory end organ of balance
cochlea tonotopical organization
- different parts respond to different frequencies
- lined with hair cells
- higher freqs on the outside, abused the most, go first
3 scalas
scala vestibuli (perilymph) scala media (endolymph) scala tympani
basilar membrane location
base of cochlea
vestibular membrane location
roof of cochlea
cilial hair fibers
attached to nerve fibers
techtorial membrane
shearing forces activates cilia movements
stereocilia
highest hair cells