The Ear

Question 1

Cerumen

Answer 1

Ear wax. Brown waxy material secreted by glands in the external auditory meatus.

Question 2

Perilymph

Answer 2

Fluid within the bony labyrinth, surrounding the membranous labyrinth.

Question 3

Endolymph

Answer 3

The fluid within the membranous labyrinth.

Question 4

Modiolus

Answer 4

Central bony core of the cochlea and is a conical-shaped structure that contains the spiral ganglion.

Question 5

Maculae

Answer 5

Static equilibrium receptors located perpendicular to each other in the utricle and saccule.

Question 6

Saccule

Answer 6

A sac of the membranous labyrinth.

Question 7

Utricle

Answer 7

Connected to the saccule by a small duct.

Question 8

Otolith

Answer 8

Calcium carbonate crystals forming a layer over the otolithic membrane.

Question 9

Ampulla

Answer 9

An enlarged swelling at the end of each semicircular canal.

Question 10

What structures are a part of the INNER ear?

Answer 10

Bony (osseous) labyrinth*
Membranous labyrinth*
Cochlea
Bony labyrinth cochlea
Cochlear duct

Question 11

What structures are a part of the MIDDLE ear?

Answer 11

Tympanic membrane
Auditory ossicles
Malleus
Incus
Stapes
Opening to auditory tubes

Question 12

What structures are a part of the OUTER ear?

Answer 12

*The pinna
*External auditory meatus
Auricular cartilage
Cerumen

Question 13

What cranial nerve is responsible for equilibrium and hearing?

Answer 13

CN VIII (Vestibulocochlear nerve)

Question 14

What cranial nerve is responsible for sight?

Answer 14

CN II (Optic nerve)

Question 15

What are the three auditory ossicles?

Answer 15

Malleus (the “hammer”)
The small bone connecting the inner
surface of the tympanic membrane and
the incus.

Incus (“anvil”)
The ossicle between the malleus and the
stapes.

Stapes (“stirrup”)
The smallest bone in the body. Its base
fits into the oval window.

Question 16

What is the difference between the round window and the oval window?

Answer 16

Oval (vestibular) window:
one of the two openings between the middle and inner ear. It is filled by the base of the stapes, which pushes inward.

Round (cochlear) window:
the other opening between the middle and inner ear, located below the oval window and covered by a secondary tympanic membrane, which bulges outward with fluid movement.

Question 17

What is the mechanism of hearing?

Answer 17

Sound waves reaching the ear are directed by the pinna to the external auditory meatus and then to the tympanic membrane.
The tympanic membrane is vibrated by the sound waves.
The malleus, connected to the tympanic membrane’s inner surface, passes on and amplifies vibrations via the incus and stapes to the window.
Vibrations of the oval window by the stapes sets the perilymph into a wave motion that travels through the scala vestibuli and scala tympani to the round window.
The round window bulges into the middle ear and then back into the scala tympani, reversing the fluid wave movement.
Vibrations of the scala vestibuli and scala tympani generate wave motion of the endolymph within the cochlear duct displacing the hair cells of the spiral organ.
The movement of the hair cells of the spiral organ develops a nerve impulse.
The nerve impulse passes through the cochlear branch of the vestibulocochlear nerve (CN VIII) to the hearing centers in the brain.

Question 18

What is the mechanism of static equilibrium?

Answer 18

Static equilibrium is concerned with “body (head) position” relative to gravity.
The otolithic membrane is moved by the weight of the otoliths under the pull of gravity.
This bends the hair cells embedded in the otolithic membrane, generating a nerve impulse.
The impulse is carried by the vestibular branch of the vestibulocochlear nerve (CN VIII).

Question 19

What is the mechanism of dynamic equilibrium?

Answer 19

When the head moves, endolymph pushes the cupula bending the hair cells.
This sends impulses via the vestibular branch of the vestibulocochlear nerve to the brain
thus detecting angular (rotational) acceleration of deceleration of the head.