I can Hear you!!!

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I can Hear you!!!

• The workings of the ear
• A human version of a Rube golberg machine

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Anatomy of the ear

• The ear is the organ that interprets sounds
• It is divided into three different regions
• The outer ear
• What you can see and easily get at
• The middle ear
• Smallest part of the ear
• The inner ear
• Where the vibrations are transformed into nervous
  impulses

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The Outer Ear

• Overall function
• Captures the sounds and concentrates them to the
  membrane
• Parts
• Auricle or Pinna
• Auditory Canal

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The outer ear

• Sub-functions
• Auricle
• captures sounds
• Auditory canal
• protects the membrane from small insects,
  bacteria and dust that could reduce hearing.
• This is also where the ceriminous glands excrete
  cerumen (ear wax)

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The middle ear

• Overall function
• Transforms wave energy into mechanical energy
• Amplifies (or attenuates) the sound
• Equilibrates pressure on either side of the
  eardrum
• Parts
• Eardrum
• Ossicles (middle ear bones)
• Eutaschian tube

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The middle ear

• Sub functions
• Eardrum
• Sensitive membrane that transfers the sound wave
  into vibrations.
• The eardrum transfers these vibrations to the
  ossicles
• Ossicles (3)
• Malleus (hammer)
• Incus (Anvil
• Stappes (stirrup)

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The middle ear

• Sub functions (continued)
• Eustachian Tube
• 4cm long tube that connects to the pharynx
• Equilibrates the air pressure on either side of
  the eardrum

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• On either sound of the eardrum there is air
  pressure. These 2 pressure must be balanced if
  they are not balanced the eardrum cannot vibrate
  and your ear is blocked. To get the ear balanced
  you must get the pressure on either side to be
  balanced. Chew, swallow will balance air
  pressure. Diving, altitude, wind will unbalance
  them

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The inner ear

• Overall function
• Transform the mechanical energy into a chemical
  energy (nervous impulse)
• Parts
• Vestibule
• Semicircular canals
• Choclea

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The inner ear

• Sub functions
• Vestibule
• Contains nerve cells that detect the bodies
  movement and that are sensitive to the
  gravitational attraction
• These cells send impulses to the cerebellum that
  allows you stay balanced

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• Sub functions
• Semicircular canals
• 3 rings filled with liquid
• They are oriented according to the three axes in
  space
• As a person moves through space, the liquid in
  these tubes moves differently. This information
  is passed on to the cerebellum.
• There is a specific part in the brain that
  combines the information received from the eye
  and from the inner ear hand eye coordination

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• Sub functions (cont.)
• Cochlea
• Round tube filled with liquid
• Where we find nerve cells able to transform
  mechanical energy into nervous impulses
• Small hairs inside the cochlea react to their own
  frequency of the movement of the liquid
• The lower frequencies stimulate the hairs at the
  end of the cochlea. High frequencies stimulate
  hairs at the start of the cochlea.
• The louder a noise, the more nerve cells will be
  stimulated

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How do we hear?

• Sound waves will cause the eardrum to vibrate.
  The eardrum vibrating pass the sound waves to the
  ossicles. This motion continues to the cochlea,
  where tiny hairs will be stimulated based on the
  frequency and strength of an auditory signal.
  These hairs stimulate nervous cells that transfer
  the information to the brain.

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From the speaker to your brain

• The path of sound
• Sound which causes the air to vibrate
• These vibrations are caught by the auricle and
  are concentrated in the auditory canal
• The vibrations cause the ear drum to vibrate,
  which then starts a chain reaction in the
  ossicles.
• The vibrations make it all the way to the
  vestibule, where they travel through liquid
• The hairs of the cochlea pick up on these
  vibrations and signal the nervous cells that then
  transfer to the brain the information via nervous
  impulse

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The path of sound

• Auricle
• Auditory canal
• Eardrum
• Ossicles
• Cochlea
• Auditory nerve
• Brain

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Waves

• Sound
• Mechanical longitudinal wave
• Sound requires a material medium to propagate
  itself (in space no one can hear you scream)
• The speed at which sound travels depends on the
  material medium
• In air 340 m/s (compared with light 300 000 km/s

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Sound

• In order to be perceived by the human ear
• 1. the vibrations have to be fast enough
• Frequency between 16 20 000 Hz
• 2. the amplitude has to be above the hearing
  limit (0dB)
• dogs can hear sound going to 80 000 Hz, bats
  to 120 000 Hz

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Decibels

• Definition
• Measures the intensity of a sound
• Humans can hear a sound with an intensity between
  0dB to 150 dB. But after a prolonged 80 dB you
  can permanently damage your hearing.

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Decibels
Whisper 30 dB
Conversation at 5 feet 60 dB
Telephone dial tone 80 dB
Truck traffic 90 dB 8 hour max
Motorcycle 100 dB 2 hour max
Power saw at 3 feet 110 dB 30 min max
Loud rock concert 115 dB 15 min max
Pain begins 125 dB
Jet engine at 100 feet 140 dB
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Taking care of your ears

• Do not use Q-tips
• Do not stick objects in your ear
• Do not listen to loud music (including earphones)
• Music at max 100 decibels
• Desensitizes the cochlea
• Eardrum can overvibrate
• Ossicles can desensitize