Anatomy and Physiology of the Outer, Middle, and Inner Ear

Pinna

The scientific name for the part of the outer ear you see; includes the ear lobe

Helix

The C-shaped outer portion of the pinna

Antihelix

The portion located just inside the helix

Concha

The deepest recess of the pinna

Tragus

Located anterior to the helix; functions as a protective flap for the opening of the ear canal

Antitragus

The prominent fold of cartilage located inferior and posterior to the tragus

The outer ear is also known as the

external auditory canal or external auditory meatus

The EAC is shaped like a

tube

average eac length

2.5 to 3 cm

average eac diameter

0.75 cm

the eac is what shaped

S-shaped

The EAC begins at the

concha

The EAC ends at the

tympanic membrane (eardrum)

Lateral 1/3 portion is

cartilage and contains hair follicles and wax glands

Medial 2/3 portion is

bony

Primary structures of the middle ear include

tympanic membrane (or eardrum), the ossicles, primary muscles, and the eustachian tube.

the ossicles are

three small middle ear bones sometimes referred to as the hammer, anvil, and stirrup, because of their shapes. their scientific names are the malleus, the incus, and the stapes.

the tympanic membrane is what shaped

oval shaped

average diameter of tympanic membrane

8 to 10 mm in adult humans

tympanic membrane is made up of how many layers

3

layers of tympanic membrane are called

epidermal (outer), fibrous (middle), and membranous (inner)

after sound passes through the tympanic membrane

it goes on to the ossicular chain

the ossicular chain is made up of

three bones called the ossicles

the ossicular chain is attached to the

tympanic membranethe

the ossicular chain is attached to the tympanic membrane via

the largest of the three bones, malleus

movement of the malleus activates the

incus

movement of the incus activates the

stapes

the stapes covers the

oval window

when sound interacts with the stapes

sound is transduced via footplate motion

footplate motion causes a

pressure wave that is transmitted to the fluid-filled inner ear via the round window

The 2 primary muscles of the middle ear are the

stapedius muscle tendon and the tensor tympani tendon

the stapedius muscle tendon connects to the

head of the stapes

the tympani tendon courses through the middle cavity to connect the

malleus

the eustachian tube connects the

middle ear cavity to the nasopharynx

the nasopharynx is the

upper nasal cavity

the reason your ears feel “stuffed up: sometimes when you get a cold or sinus infection is due to

the connection of the nasal cavity to the middle ear cavity

activation of the acoustic reflex is due to

facial motor nerve or cranial nerve

The inner ear is responsible for

sensation of hearing and maintaining balance and sensing motion

Cochlea

sensory organ for hearing that is bone-covered, snail0shaped and located within an area of the temporal bone called the petrous portion

the petrious portion of the inner ear is the ___ in the human body

hardest and most dense bone

the cochlea contains 2 cochlear fluids known as

endolymph and perilymph

the cochlea contains

cochlear fluids, hair cells and supporting cells, and the basilar, tectorial, Reissner’s membrane, and the vestibule that leads to balance organs

membranous cochlea is housed within the

cochlea

the membranous cochlea consists of three fluid filled ducts

the scala vestibuli, the scala tympani, and the scala media

endolymph fluid fills the

scala media

perilymph fluid fills the

scala vestibuli and scala tympani

the cochlear ducts connect to the

oval window via the vestibule

the motion of the stapes foot place transfers energy to the

scala vestibuli

the membranous cochlea round window is located

at the end of the scala tympani

The 3 scalae of the cochlea are separated by two primary cochlear membranes

reissner’s membrane and the basilar membrane

reissner’s membrane

made up of two layers of cells and becomes wider from the base to the apex. provides support to the scala media

basilar membrane

wider at the apex versus the base. supports the organ of corti and houses the cochlear sensory cells.

the organ of corti

end organ of hearing.

the organ of corti is located

inferior to the tectorial membrane and superior to the basilar membrane

the organ of corti contains

supporting structures, sensory hair cells, membranes, and nerve fibers

The membranous cochlea is supported by the

spiral ligament and stria vascularis

the spiral ligament

extends through the cochlea and provides support to reissner’s membrane and the basilar membrane

stria vascularis

makes up the upper part of the spiral ligament

the stria vascularis plays a key role in

production and absorption of endolymph

endolypm is important for

metabolism within the cochlea

the cells contained within the stria vascularis are involved in

potassium ion transport throughout the cochlea

potassium ion is important for

function of the inner ear

located along the organ of corti are the

inner and outer cochlear hair cells

tonotropic organization

the base of the cochlea responds to high-frequency sounds and cells located in the apex respond to low frequency sounds.

tonotopic organization occurs

throughout the auditory system

the outer hair cells are organized in

rows of 3 to 5 layers, with a total of about 12,000

which hair cells are longer

outer hair cells

outer hair cells have special motile preperties that allow them to

expand and contract when innervated by auditory input

outer hair cells that code low frequencies are

longer than high frequency outer hair cells

outer hair cells are structurally supported by

stereocilia

inner hair cells are organized in a

single row and total about 3500.

inner hair cells have fewer supportive

stereocilia

once auditory input is coded and processed by the cochlea

it is then passed to the auditory nerve

the auditory nerve connects

the cochlea to the brainstem

the auditory nerve contains

two types of nerve fibers

type I fibers

connect to the inner hair cells and make up about 90% of all nerve fibers

type II fibers

connects to the outer hair cells and make up about 10% of all auditory nerve fibers

both type I and type II auditory nerve fibers play a role in

synchronous firing of the auditory nerve and the propagation of sound a long the ascending auditory pathway and up to the brain

The central auditory nervous system is a system of

ascending auditory neurons from the brain stem to the auditory cortex and temporal lobe

The auditory cortex connects to the ascending neuron via

the medial geniculate body

after reaching the auditory cortex the input crosses the

midline of the brain, a dense cluster of cells known as the corpus callosum

after crossing the corpus callosum, the auditory inputt is processed by the

opposite side of the brain