Outer and Middle Ear Anatomy and Physiology - SPPA 3510

8 structures of the outer ear

superior crus

inferior crus

helix

antihelix

tragus

antitragus

concha

lobule

s-shaped passage of skin-covered cartilage and bone, containing a bend called the _____

external auditory canal, isthmus

5 structures of the tympanic membrane

posterior and anterior malleolar folds

pars tensa

pars flacida

umbo

cone of light

deepest point of the tympanic membrane

umbo

the cone of light is at a ____ position in the RIGHT ear and a ____ position in the LEFT ear

5 o’clock, 7 o’clock

portions of the malleus visible through the tympanic membrane

lateral process and handle

acoustic purposes of the outer ear

collect, funnel, and pre-amplify sounds

protective purposes of the outer ear

depth and rigidity

hairs and cerumen

epithelial migration

epithelial migration

skin cells of the external auditory canal migrate from the tympanic membrane to the opening in the pinna, carrying out dead skin cells and other particles

3 structures of the middle ear

eustachian tube

muscles and ligaments

ossicles: malleus, incus, stapes

parts of the malleus

head

anterior and lateral processes

neck

manubrium (handle)

parts of the incus

head

articulation with malleus

short and long process

lenticular process

parts of the stapes

head

anterior and posterior crus

footplate

3 purposes of the middle ear

acoustic reflex, equalizing pressure, impedance matching

how does the acoustic reflex protect the ear?

it contracts the muscles to create a stiffness in the ossicular chain, preventing it from effectively transmitting the acoustic signal

3 caveats of the acoustic reflex

1. 10 millisecond delay from when sound enters the ear (sound can’t be too short)

2. will decrease intensity, but not necessarily into a safe range (sound can’t be too loud)

3. muscles will eventually fatigue and the effect will wear off (sound can’t be too long)

why is the eustachian tube necessary?

air in the middle ear cavity is slowly absorbed into the surrounding mucous membrane.

this decreases the air pressure in the cavity, creating an uncomfortable vacuum.

the eustachian tube opens to replenish air.

impedance mismatch

the acoustic signal loses energy when it travels from the air-filled middle ear to the fluid-filled inner ear

what is impedance matching?

mechanism of the middle ear which boosts the acoustic signal in preparation for entering the fluid-filled inner ear.

3 elements of impedance matching

1. pressure of the signal increases when it’s forced from the large tympanic membrane to the small stapes footplate

2. lever action of the ossicles creates force that boosts the signal

3. buckling of the tympanic membrane: flexible edges buckle to funnel sound towards more rigid center