The Ear and Hearing

IB BiologyNeurology UnitOption E

The EarThe Ear

Functions:

Hearing

Equilibrium (balance)

Utilizes mechanoreceptors

Anatomy of the EarAnatomy of the Ear

Three areas Outer (external) Ear

Middle Ear

Inner Ear

The External EarThe External Ear

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Function:

Hearing only

Structures: Pinna

(auricle)

External auditory canal

Figure 8.12

Pinna

Collects soundwaves

The External Auditory CanalThe External Auditory Canal

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Narrow chamber in the temporal bone

Lined with skin

Contains ceruminous glands

Ends at the tympanic membrane

Mastoid Process

Bony ridge behind the pinna

Provides support to the external ear and posterior wall of the middle ear cavity

The Middle Ear The Middle Ear

Slide 8.24a

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Air-filled cavity within the temporal bone

Function: Hearing only

Separated from outer ear by

tympanic membrane

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 EarBones of the Middle Ear

Slide 8.25a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Ossicles:

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Figure 8.12

Ossicles Act as a lever

system Action initiated

from vibration of tympanic membrane

A = malleusB = incusC = 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 incus5. Incus contacts stapes6. 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 EARINNER EAR

Slide 8.26a

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FUNCTIONS:

Hearing!

Balance!

Fluid-filled (perilymph)

Figure 8.12

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

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

Structures of the Inner Ear (Cont.)

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 How Sound Travels Through The Ear...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