Anatomy of the Ear (v2.0)


Lets learn about the ear.
Our ears sense sound waves carried in the air.
Lets take a closer look. The ear consists of three main divisions.
The external or outer ear includes the pinna or auricle.
And the external auditory meatus. The tympanic membrane is considered the boundary
between the external and middle ear. The middle ear consists of the auditory ossicles
which include the malleus, incus and stapes and the Eustachian tube that helps to equalize
pressure inside of the ear. The inner ear consists of three main parts.
The semicircular canals the vestibule..and the cochlea.
The auditory or vestibulocochlear nerve cranial nerve 8 carries the information from the inner
ear to the brain for processing. Lets look at how sound is processed by the
ear. Sound waves enter the external auditory meatus
and travel to the tympanic membrane causing it to vibrate.
The vibrations are carried by the malleus, incus and stapes to the inner ear. The stapes
connects to the inner ear at the oval window. Sound is further processed in the cochlea.
There are three fluid filled chambers inside of the cochlea. These are the scala vestibule,
scala media and scala tympani. The vibrations at the oval window are transmitted
throughout the fluid. The middle chamber or scala media contains
the organ of hearing called the organ of Corti. The organ of Corti consists of two membranes
connected by hair cells. The fluid vibrations are transmitted along
the basilar membrane and picked up by the hair cells.
The hair cells respond by sending impulses which travel to the brain via cranial nerve
8. The brain interprets these impulses as hearing.
The inner ear also senses changes in position known as static equilibrium.
Static equilibrium is sensed in the vestibule. Inside of the vestibule are two areas called
the utricle and saccule. Both of these areas contain a macula.
Here is a little more detailed picture of the macula.
The macula contains a membrane called the otolithic membrane.
Hair cells are connected to the membrane. A series of small crystalline structures called
otoliths sit on top of the membrane. When the head changes position the otoliths
pull on the membrane. This causes the tiny stereocilia on the hair
cells to bend. The bending of hair cells is converted to
impulses that travel to cranial nerve 8 and to the brain for processing.
The semicircular canals sense changes in movement. There are three semicircular canals.
Each semicircular canal contains an area called the ampulla.
Inside the ampulla is a structure called the crista ampullaris.
The top portion of the crista ampullaris is called the cuplula.
Changes in motion or acceleration cause fluid called endolymph inside of the semicircular
canals to move. The fluid flows over the cupula causing it
to bend. The stereocilia of the hair cells connected
to the crista ampullaris also bend and the cells transmit impulses to cranial nerve 8.
The ear processes hearing, changes in position or static equilibrium and changes in movement
or dynamic equilibrium. We hope you have learned something about the
ear and see you next time.

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