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The Ear and Hearing
IB Biology
Neurology Unit
Option E
The Ear
 Functions:
 Hearing
 Equilibrium (balance)
 Utilizes mechanoreceptors
Anatomy of the Ear
 Three areas
 Outer (external) Ear
 Middle Ear
 Inner Ear
The External Ear
 Function:
Hearing only
 Structures:
 Pinna
(auricle)
 External
auditory canal
Figure 8.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.22
Pinna
 Collects soundwaves
The External Auditory Canal
 Narrow chamber in the temporal bone
 Lined with skin
 Contains ceruminous glands
 Ends at the tympanic membrane
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.23
Mastoid Process
 Bony ridge behind
the pinna
 Provides support to
the external ear
and posterior wall
of the middle ear
cavity
The Middle Ear
 Air-filled cavity within the temporal bone
 Function: Hearing only
 Separated from outer ear by
tympanic membrane
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Tympanic Membrane
 Thin membrane
 Forms boundary
between outer and
middle ear
 Vibrates in
response to sound
 Changes acoustical
energy into
mechanical energy
Bones of the Middle Ear
 Ossicles:
 Malleus
(hammer)
 Incus (anvil)
 Stapes (stirrip)
Figure 8.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Ossicles
 Act as a lever
system
 Action initiated
from vibration of
tympanic
membrane
A = malleus
B = incus
C = stapes
External and Middle Ear Functioning:
An Overview
1. Soundwaves (collected by pinna) travel
through external auditory canal
2. Soundwaves lead to tympanic membrane
vibrations.
3. Tympanic membrane vibrations move
malleus
4. Malleus contacts incus
5. Incus contacts stapes
6. Stapes movement initiates inner ear
response!!
Eustachian Tube
 Lined with mucus
membrane; connects
middle ear to back of
the throat
(nasopharynx)
 Equalizes air pressure
 Normally closed except
during yawning or
swallowing
 Not a part of the
hearing process
INNER EAR
 FUNCTIONS:
Hearing!
Balance!
 Fluid-filled
(perilymph)
Figure 8.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Structures of the Inner Ear
Cochlea
Vestibule
Semicircular
Canals
Cochlea
 snail-shaped organ with a series of
fluid-filled tunnels
 converts mechanical energy into
electrical energy
Structures of the Inner Ear (Cont.)

Oval Window – located at the base
of the stapes; when the stapes vibrates,
the cochlear fluid (perilymph) is set into
motion

Round Window – functions as the pressure
relief port for the fluid set into motion initially
by the movement of the stapes in the oval
window
Organ of Corti
 The end organ of
hearing; contains
stereocilia and hair
cells.
Central Auditory System
 8th Cranial Nerve or “Auditory Nerve”
carries signals from cochlea to brain
 Fibers of the auditory nerve are
present in the hair cells of the inner
ear
 Auditory Cortex: Temporal lobe
of the brain where sound is
perceived and analyzed
How Sound Travels Through
The Ear...
Acoustic energy, in the form of sound waves, is channeled into
the ear canal by the pinna. Sound waves strike the tympanic
membrane, causing it to vibrate like a drum, and changing it
into mechanical energy. The malleus, which is attached to the
tympanic membrane, starts the ossicles into motion. (The
middle ear components mechanically amplify sound). The
stapes moves in and out of the oval window of the cochlea
creating a fluid motion. The fluid movement within the
cochlea causes membranes in the Organ of Corti to shear
against the hair cells. This creates an electrical signal which
is sent via the Auditory Nerve to the brain, where sound is
interpreted!
Vestibular System
 Consists of three
semi-circular canals
 Shares fluid with the
cochlea
 Controls balance
 No part in hearing
process