Hearing: How do we hear?

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Hearing How do we hear?
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Hearing The Nature of Sound

• Module 9 Sensation

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Sound

• Sound, like light, comes in waves
• Sound is vibration
• Features of sound include
• Pitch
• Hertz
• decibels

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Pitch

• A sounds 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)

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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

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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
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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
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Decibel (dB)

• A measure of the height of the sound wave
• Determines the loudness of the sound
• Sometimes called amplitude

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What are good sounds versus bad

• What volume do you think is okay?
• Not good, not bad?
• Bad?

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Hearing The Structure of the Auditory System

• Module 9 Sensation

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Break It Down

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

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PINNA
The visible part of the outer ear.

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

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Parts of the Ear Sound Waves
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Auditory Canal

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

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Parts of the Ear Auditory Canal
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THE MIDDLE EAR
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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

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Parts of the Ear Tympanic Membrane
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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

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Parts of the Ear - Occicles
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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.

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Parts of the Ear Oval Window
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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

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Parts of the Ear - Cochlea
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Hair Cells

• The receptor cells for hearing in the cochlea
  that change sound vibrations into neural impulses
• Transduction!

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Parts of the Ear - Hair Cells
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Parts of the Ear Oval Window
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Auditory Nerve

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

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Parts of the Ear Auditory Nerve
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Divisions of the Ear

• Ears structure can be divided into
• The outer ear
• The middle ear
• The inner ear

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Divisions of the Ear
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Divisions of the Ear
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Divisions of the Ear
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REVIEW

• The Ossicles amplify the vibration of the eardrum

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

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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
  

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REVIEW

• Where vibrations are changed into neural impulses
  so that the brain can read / interpret the sound
  
• What are the receptors cells for hearing?

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Problems with hearing

• Conduction deafness (middle ear damage)
• Nerve deafness (hair cell or auditory nerve
  damage)

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Hearing Sound Localization

• Module 9 Sensation

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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?

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Localization of Sound
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Another sense in your ears?

• Is there another sense in your ear?

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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.

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Parts of the Ear Semicircular Canals
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Parts of the Ear Semicircular Canals
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Semicircular canal

• What situations will affect the semicircular canal

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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.