AP II CHP15

Three major areas of the ear

External ear, middle ear, internal ear

Function of the external and middle ear

hearing only

What two structures are apart of the external ear

Auricle and external acoustic meatus

Primary function of the auricle

Funnels sound waves into the external acoustic meatus

Tissue composition of the auricle

Elastic cartilage covered with thin skin

Name of the auricle’s rim

Helix

What is the main structural feature of the lobule

it lacks supporting cartilage

External acoustic meatus

Canal leading from the auricle to the eardrum

General function of the external ear

Collects and directs sound waves inward

Which ear region contains elastic cartilage?

Auricle

Which ear regions participate in hearing only?

External ear and middle ear

What type of connective tissue makes up the external acoustic meatus?

elastic cartilage

What bone forms the deeper part of the external acoustic meatus?

Temporal bone

Glands that produce cerumen

Ceruminous glands

Type of secretion produced by ceruminous glands

Yellow-brown waxy cerumen (earwax)

Function of cerumen

Traps foreign bodies and repels insects

What mechanism naturally moves earwax outward?

Jaw movements during talking and eating

What occurs when there is an excessive accumulation of cerumen?

compaction

What is the boundary between the outer and middle ear?

Tympanic membrane

What is the tissue composition of the tympanic membrane?

Thin, translucent connective tissue

What covers the external portion of the tympanic membrane?

Skin

What is the internal covering of the tympanic membrane?

Mucosa

Shape of the tympanic membrane

Flattened cone with apex protruding medially

What is the effect of sound waves on the tympanic membrane?

it will vibrate

Location of the middle ear

Petrous part of the temporal bone

What are the two openings in the medial wall of the middle ear?

Oval window and round window

Superior portion of the middle ear cavity

Epitympanic recess

What connects the middle ear to mastoid air cells?

Mastoid antrum

What artery is adjacent to the anterior wall of the middle ear?

Internal carotid artery

Original name of the pharyngotympanic tube

Eustachian tube

What connection is formed by the pharyngotympanic tube?

middle ear to the nasopharynx

Direction of the pharyngotympanic tube

Runs obliquely downward

Why is the middle ear mucosa continuous with pharyngeal mucosa?

the pharyngotympanic tube connects them

Normal state of the pharyngotympanic tube

Flattened and closed

What actions open the pharyngotympanic tube?

Swallowing or yawning

What is the purpose of opening the pharyngotympanic tube?

Equalizes pressure in the middle ear with external air pressure

Effect of unequal pressure on the eardrum

Distorts sound because the eardrum cannot vibrate freely

What is the cause of the ear-popping sensation?

Pressures equalizing between the middle ear and external air

Most common cause of hearing loss in children

Otitis media

What is the reason children are prone to otitis media?

Short, horizontal pharyngotympanic tubes

How is the eardrum affected during acute otitis media?

Bulging, inflamed, and red

Three auditory ossicles of the middle ear

Malleus, incus, stapes

Malleus

Ossicle attached to the eardrum

Stapes

Ossicle whose base fits into the oval window

Incus

Ossicle that articulates with malleus laterally and stapes medially

Function of the auditory ossicles

Transmits eardrum vibrations to the oval window

Effect of oval window movement

Sets internal ear fluids in motion

Tensor tympani

Muscle inserting on the malleus

Stapedius

Muscle attaching to the stapes

What occurs when loud sounds hit the ear?

muscles contract reflexively to limit the ossicles’ vibration and minimize damage to the hearing receptors

What structures suspending the ossicles?

Tiny ligaments

What type of joints link the ossicles?

Tiny synovial joints

Why is the internal ear called the labyrinth?

its complex, maze‑like shape.

Where is the internal ear located?

Deep in the petrous part of the temporal bone behind the eye socket.

What is the membranous labyrinth?

A continuous series of membranous sacs and ducts within the bony labyrinth.

What are the two major divisions of the internal ear?

The bony labyrinth and the membranous labyrinth.

What fluid fills the bony labyrinth?

Perilymph.

Perilymph resembles which body fluid?

Cerebrospinal fluid

What fluid fills the interior of the membranous labyrinth?

Endolymph.

Endolymph is chemically similar to what?

K⁺‑rich intracellular fluid.

Where is the membranous labyrinth positioned within the ear?

Suspended in the surrounding perilymph.

What do perilymph and endolymph conduct?

Sound vibrations which are involved in hearing.

What forces do the internal ear fluids respond to?

Mechanical forces during changes in body position and acceleration.

What structural feature allows the internal ear to house delicate receptors?

Its deep, protected location within the temporal bone.

How does the membranous labyrinth relate to the bony labyrinth?

It generally follows the contours of the bony labyrinth.

What are the three regions of the bony labyrinth?

the vestibule, the semicircular canals, and the cochlea

What is the vestibule?

central egg‑shaped cavity of the bony labyrinth.

Which structure is found in the lateral wall of the vestibule?

The oval window.

Which two membranous sacs are suspended in the vestibular perilymph?

The saccule and utricle.

Which vestibular sac is continuous with the cochlear duct?

The saccule.

Which vestibular sac is continuous with the semicircular ducts?

The utricle.

What receptor regions are housed in the saccule and utricle?

Maculae.

What do maculae detect?

Gravity and changes in head position.

How many semicircular canals are in each internal ear?

Three: anterior, posterior, and lateral.

How is the lateral semicircular canal oriented?

Horizontally.

What structure snakes through each semicircular canal?

A membranous semicircular duct.

What is the ampulla?

The enlarged end of each semicircular duct.

What receptor region is housed in each ampulla?

The crista ampullaris.

What is the cochlea?

A spiral, conical, bony chamber about the size of a split pea.

How many turns does the cochlea make around the modiolus?

About 2½

What is the modiolus?

The bony pillar around which the cochlea coils.

What structure runs through the center of the cochlea?

The membranous cochlear duct.

What does the cochlear duct house?

The spiral organ (organ of Corti); the receptor for hearing.

What divides the bony cochlea into three scalae?

The cochlear duct and the osseous spiral lamina.

What fluid fills the scala vestibuli?

Perilymph.

What fluid fills the scala media?

Endolymph.

What fluid fills the scala tympani?

Perilymph.

Where does the scala vestibuli begin and terminate?

At the oval window; at the round window

What is the helicotrema?

The region at the cochlear apex where the scala vestibuli and scala tympani are continuous.

What forms the roof of the cochlear duct?

The vestibular membrane.

What supports the spiral organ?

The basilar membrane.

How does the basilar membrane change from base to apex?

It is narrow and thick near the oval window and wider and thinner near the apex.

What cells serve as the hearing receptors?

Cochlear hair cells.

How are cochlear hair cells arranged?

One row of inner hair cells and three rows of outer hair cells.

Between which two membranes are the hair cells positioned?

The tectorial and basilar membranes.

Which nerve fibers coil around the bases of hair cells?

Afferent fibers of the cochlear nerve (a division of CN VIII).

What medium does sound require for transmission?

An elastic medium that physically transmits vibrations.

Why does thunder arrive after lightning?

Sound travels much slower than light.

What is the speed of sound in dry air?

About 331 m/s.