The Ear Is Involved in Hearing and Equilibrium
LEARNING OBJECTIVES
1.
Identify
structures of the ear, including those of
the outer ear, middle ear, and inner ear.
2.
Explain
how the ear converts sound waves into
nerve impulses and the path those impulses
take to the brain.
3.
Describe
the structures of the ear involved in
static and dynamic equilibrium.
4.
Outline
the neural pathways involved in equilib-
rium.
onsider a ballet dancer. She must hear the mu-
sic so that she knows her cues as well as the
proper timing and rhythm for the execution of
her steps. Her body must be aware at all times
of the positions of her limbs with respect to gravity and
make minute changes in muscles so she can stay balanced
T he e a r consists o f th re e p arts: th e o u te r ear,
th e m iddle ear, and th e inner e a r • Figure 8.11
on her toes. The receptors for both the sense of hearing and
the sense of balance, or equilibrium, are located in the ears.
Let’s take a closer look at the structures of the ear.
The Ear Is Composed of
Three Distinct Regions
The ear consists of three parts: the outer ear, middle
ear, and inner ear (
Figure 8.11
). The outer ear mainly
receives and directs sound waves into the ear canal. The
middle ear conveys sound vibrations to the inner ear,
which houses the receptors for hearing and balance. The
middle ear and inner ear are located within the temporal
bone of the skull. The spaces of the outer ear and middle
ear are filled with air, which allows
the
eardrum
(tympanic mem-
brane)
and auditory
ossicles
to
vibrate rapidly and freely.
ossicles
(OS-si-kuls)
Small bones of the
middle ear.
Outer
ear
Middle
ear
Inner
ear
Temporal bone
>. \v.
.-T.
Ceruminous glands
secrete cerumen
(earwax), which
protects ear from
foreign objects.
Auricle collects sound
waves and directs
them to external
auditory canal.
External auditory
canal
directs sound waves to
eardrum (tympanic
membrane).
Auditory ossicles transmit vibrations
to oval window of inner ear
(Malleus, incus, stapes).
Eardrum
(tympanic
membrane) vibrates with
incoming sound waves.
Outer ear
(] Middle ear
Internal ear
Elastic '
cartilage
Round window
eliminates the
sound waves
that have been
heard.
Semicircular canals are
also involved in balance.
Vestibule contains two
sacs involved in balance
(utricle, saccule).
Vestibulocochlear (VIII)
nerve transmits nerve
impulses to brain:
• Vestibular branch
• Cochlear branch
Cochlea connects
fluid pressure waves
into action potentials.
Auditory (eustachian) tube
connects middle ear with
nasopharynx and equalizes
air pressure behind eardrum.
The Ear is involved in Hearing and Equilibrium 241
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