Hearing: How do we hear?

Hearing: The Nature of Sound

Module 9: Sensation

Sound

• Sound, like light, comes in waves

• Sound is vibration

• Features of sound include:

–Pitch

–Hertz

–decibels

Pitch

• A sound’s highness or lowness

• Dependent on the frequency of the sound wave – the more “waves per second” the higher the frequency or pitch

• Is measured as hertz (Hz)

Hertz (Hz)

• A measure of the number of sound wave peaks per second; measures “frequency”

• Determines the pitch of the sound

• One Hertz = one vibration per second

Low Pitch

• Wave peaks are far apart

Human hearing goes from 20 Hz to 20,000 Hz although some ears (and speakers) are

better than others

High Pitch

• As pitch increases, so do the number of waves

Remember - Human hearing goes from 20 Hz to 20,000 Hz note: a kilohertz is 1,000 hertz

so 20 kilohertz equals 20,000 hertz

Decibel (dB)

• A measure of the height of the sound wave

• Determines the loudness of the sound

• Sometimes called amplitude

What are good sounds versus bad

• What volume do you think is okay?

• Not good, not bad?

• Bad?

Hearing: The Structure of the

Auditory System

Module 9: Sensation

Break It Down

• Sound waves are collected in the outer ear, amplified in the middle ear, and transduced, in the inner ear.

PINNA

• It collects sound and directs it into the outer ear canal.

The visible part of the outer

ear.

Parts of the Ear – Sound Waves

• The opening through which sound waves travel as they move into the ear for processing

• Ends at the eardrum

Auditory Canal

Parts of the Ear – Auditory Canal

THE MIDDLE EAR

Eardrum

•Also called the tympanic membrane. A thin membrane that vibrates when sound waves reach it.

• it transfers sound vibration from the air to the tiny bones of the middle ear

•Can be damaged by objects in the ear or exceptionally loud noises

Parts of the Ear – Tympanic Membrane

Bones of the middle ear - Ossicles

•Three tiny bones that transfer sound waves from the eardrum to the cochlea

•Hammer, anvil and stirrup–Fun fact: the stirrup is the smallest bone in the human body – only .25 cm

Parts of the Ear - Occicles

Oval Window•The point on the surface of

the cochlea which receives the sound vibration from the bones of the middle ear (ossicles)

•As the oval window vibrates, the fluid in the cochlea vibrates.

Parts of the Ear – Oval Window

Cochlea

•A hearing organ where sound waves are changed into neural impulses (transduction)

•The major organ of hearing•Filled with fluid; a snail

shaped body tube

Parts of the Ear - Cochlea

Hair Cells• The receptor cells for hearing in the

cochlea that change sound vibrations into neural impulses

• Transduction!

Parts of the Ear - Hair Cells

Parts of the Ear – Oval Window

Auditory Nerve

• The nerve that carries sound information from the ears to the temporal lobes of the brain

Parts of the Ear – Auditory Nerve

Divisions of the Ear

• Ear’s structure can be divided into:

–The outer ear

–The middle ear

–The inner ear

Divisions of the Ear

Divisions of the Ear

Divisions of the Ear

REVIEW

• The Ossicles amplify the vibration of the eardrum

HammerAnvil

Stirrup

Ear Drum

Movement of the fluid causes the hair cells to move which causes TRANSDUCTION!

REVIEW

• Sound comes into the ear • Goes through the ear canal to the

eardrum• Ear drum changes sound into

vibrations• Vibrations go through middle ear

to the inner ear –

REVIEW

• Where vibrations are changed into neural impulses so that the brain can read / interpret the sound –

• What are the receptors cells for hearing?

Problems with hearing• Conduction deafness* (middle ear damage)

• Nerve deafness (hair cell or auditory nerve damage)

Hearing: Sound Localization

Module 9: Sensation

Localization of Sound

• Locating where sound is originating from

• Done through two cues:

–Which ear hears the sound first?

–Which ear hears the louder sound?

Localization of Sound

Another sense in your ears?• Is there another sense in your

ear?

Vestibular Sense• The system for sensing body

orientation and balance• Relies on fluid in the semicircular

canals of the inner ear• Spinning in circles disrupts the

fluid.

Parts of the Ear – Semicircular Canals

Parts of the Ear – Semicircular Canals

Semicircular canal

• What situations will affect the semicircular canal

EUSTACHIAN TUBE

• A tube that connects the middle ear to the back of the nose; it equalizes the pressure between the middle ear and the air outside. When you "pop" your ears as you change altitude (going up a mountain or in an airplane), you are equalizing the air pressure in your middle ear.