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Lecture 2

BIOL 1320 Lecture Notes - Lecture 2: Ear Canal, Eardrum, Basilar Membrane

Course Code
BIOL 1320
Carol Chaia Halpern

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January 26, 2016
The Ear and Hearing
I. Introduction
a. Capacity allow us to dicern and perceive sound
b. 3 regions
II. Outer most region: outer ear, middle, and inner, which we cannot see
a. Outer: Pinna: covered by skin, to connect sound waves and it directs them into the
canal which is the external auditory canal head out against the ear drum tympanic
membrane the boundary between outer and inner ear.
b. The tympanic membrane the middle ear
i. Vibrates to sound waves: pressure that is generated against molecules in
the air.
ii. Like a pressure up against these molecules, creates a pressure on the
tympanic membrane that vibrates back and forth.
iii. Vibrations come in various frequencies and amplitudes.
iv. Comes in through external auditory canal tympanic vibrates
c. External auditory canal with wax, pushing wax against the tympanic membrane
III. Middle ear: bony compartment, consists of the 3 auditory ossicles
a. The malleus that s attached to membrane, incus stapes: attached to ligaments
i. They vibrate with the tympanic, activates malleus, then to the incus then to
the stapes
ii. Footplate of the stapes vibrates against the oval window
iii. Oval window is the opening into the inner ear.
iv. Vibration is generated received by the stapes into the inner ear
v. Amplified by the action of the ossicles
b. Other canal: pahyngotympanic other tube, opens into the throat
i. Released place for the pressure waves, pressure up against tympanic
membranes, chew gum or open your mouth, swallow
ii. When you have a cold mucus accumulates enter into the tube
iii. More painful to fly because of the difficulty to release pressure
iv. Increase to infection from middle ear
1. End up affecting the middle ear. The pressure is released by
inserting tiny tubes into the tympanic membrane, draining of
mucus. They fall out on their own.
2. Tympanic membrane can repair themselves in young ones.
v. Oval window, another one is called the round window
1. Travel into the inner ear come out after they do what they do
c. Round window
i. Come out of the round window
ii. So that the pressure doesn’t accumulate
iii. Released the the auditory tube
IV. Inner Ear: loud sounds can affect our sense of balance, disorienting to the brain
a. Vesitbule: contain the structures in balance
b. Semicircula canals: contain the structures in balance
c. Cochlea: involved in hearing
i. Involved in hearing: organ of corti/spiral organ
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ii. Consists of receptor cells, in the case of hearing the mechanoreceptors
iii. Stimulated by movement and by a distortion of hair cells.
iv. Bony structure, it has several components if we look inside
1. Scala vestibule and a scala tympani
2. A duct, the 3 dimensions, it is challenging, pretend we can open up
the snail into more of a 2D shape
3. Have oval window and round window, Cochlea duct, fluid in there
(perilymph) inside cochlea duct, similar but different called
endolymph in duct
4. Bottom part of cochlea duct has a membrane called the basilar
membrane organ of corti is in the basilar membrane
v. Vibrations vibrate basilar membrane that leads to the movement of hairs
vi. Come in through oval window causes a disturbance in the perilymph, like
waves. Some of the waves can cross the cocular duct membrane, some just
go around
1. The ones the cross and enter into the cochlea duct, leave to the
permeation in the endolymph, then that vibrates the basilar
membrane and then organ of corti.
2. That is the process of how that takes place.
3. Cochlea duct of not, come out through the round window. Has do
with that frequency to cross the duct
January 28, 2016
I. Pathway of sound
a. From outside in
b. Put pressure on tympanic membrane, put a different frequency, translated into the
vibrates that come in through the middle ear through the ossicles, go to the
cochlea duct (inner ear) depending on the frequency the sound wave will
penetrate at different level.
c. Perilymph and endo lymph which will activate the basilar membrane
d. Waves represent sound waves. Sometimes low frequency cannot penetrate. Come
out and exit through the round window.
e. Cross section of the cochlea, bony part, projection shelf, bordered by vestibule
and the bottom is the scala tympani above is the basilar membrane organ of corti
is imbedded in the basilar membrane.
f. Sound waves come in and disturb the perilymph in the scala vestibule, at a certain
frequency they can come into the cochlea duct, it is like creating waves in the sea.
Cause a vibrating in the basilar membrane
g. Organ of corti: has hair cell, has various kinds of projections, there are some
supporting cells
i. Membrane still gelatinous membrane, tectorial membrane
ii. What happens when the basilar membrane
1. Hair cells brush up against the tectorial membrane, the hairs are in
contact with the tectorial membrane
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