Cochlea – Anatomy of the Auditory System and Vestibular System | Lecturio


the cochlea is the structure of the

inner ear that harbors the cellular

machinery of the auditory apparatus and

its characteristics are very very unique

in order for it to carry out its

marvelous function and so the first

thing that we that I want you to know

about the cochlea is that it has two

labyrinths and one of these is the

osseous labyrinth and so the bony canal

of the cochlea is along and through here

here's the outer bony wall of the

cochlea as it spirals internally within

the inner ear and then here's the other

side of that bony canal that coils

within the inner ear running within this

osseous labyrinth is a membranous

component and this is the memory Ness

labyrinth and we see it in blue and it

too will follow the coiled nature the

bony labyrinth and then it'll end here

finally at the apex of that coiled

cochlea if we take a cross section

through the bony or osseous labyrinth

and the membranous labyrinth this is the

profile that we'll see and in that

profile we will have three Scylla so

here is the scale of a stimuli here's

the outer portion of the osseous

labyrinth on the opposite side we have

the scale a-- timpani and you can

appreciate the bony wall of the osseous

labyrinth here

and then between the scale of a stimuli

and the skaila tympani we have this gala

media and this is also referred to as

the cochlear duct now the cochlear duct

has a specialized fluid called the

endolymph the scale of vestibuli and the

scala tympani have a extracellular fluid

that's termed apparel lymph the

endolymph however is very very unique in

its ionic concentration normally

extracellular fluid is very very low and


however the scale of media its endolymph

is extremely high in potassium ion

concentration and this assists very

greatly in the depolarization of the

hair cells and reduces the ATP out

requirements of the hair cells as well

the endolymph is secreted by a

specialized epithelium called the

Australia vascular s and that's shown

here on this aspect of the skaila media

the scaly are separated from one another

by membranes this membrane is separating

the scale of a stimuli from the scale of

media and this is aptly termed in blue

here the scale excuse me the vestibular

membrane and then the membrane that

separates the scale of media from the

skaila tympani

company here media here shaded in blue

is the basilar membrane

now when we think about audition the

organ of Corti within the scale of media

is literally the masterpiece of cellular

micro architecture

this is the apparatus that's going to be

responsible for taking the sound waves

and converting them into action

potentials the organ of Corti contains

numerous structures but the ones that

were most interested in are those shaded

in green and these are the hair cells of

the organ of Corti now these are the

outer hair cells and then this would be

a row of inner hair cells and the

stereocilia the stereocilia are embedded

in the tectorial membrane that we see

and through here the hair cells in

association with some supporting cells

are anchored to the basilar membrane

that we see down in through here and

that is labeled here for you the cochlea

along the basilar membrane is frequency

tuned and what you need to understand

about the frequency tuning of the

basilar membrane is that high frequency

sounds well allow the basilar membrane

in the base of the cochlea to start to

vibrate they are more sensitive to high

frequency sound waves and so the basilar

membrane here will start to vibrate and

that will cause movement of the hair

cells because they're embedded in a

tectorial membrane and the nel start to

depolarize in response to high frequency

sound waves

low-frequency sound waves are gonna be

toward the apex of the cochlea and at

this point that area of the basilar

membrane will start to vibrate in

response and then the rest of the

basilar membrane is fine-tuned again

from high to low in between those areas

now I want to guide you through the

innervation of the cochlea and so once

the hair cells have become depolarized

action potentials will be conveyed along

the nerve fibers that make up the

cochlear component of cranial nerve

number 8 and so we see innervation here

of the hair cell with a cochlear nerve

fiber and then that's running through a

bony canal in through here and we're

going to follow that out toward the

central nervous system those nerve

fibers will start to come together and

in this area

we'll have nerve cell bodies of those

cochlear nerve afferent fibers residing

within this spiral ganglion the fibers

will continue in this direction and in

this view will see those fibers

extending away from the ganglion within

the cochlear nerve itself this is within

the inner ear and so it needs to exit

the inner ear to get to the central

nervous system and so it will exit

through the internal acoustic meatus

that we see here and then the cochlear

nerve along with the vestibular nerve

will form cranial nerve number 8 that we

see in through here