THE EAR

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THE EAR

• is a sensory organ responsible for both hearing
  and maintenance of balance
• composed of three sections the outer, middle and
  inner ear.

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The Outer Ear

• The Pinna the outer flap that funnels sound
  towards the auditory canal
• Auditory Canal a tube that carries sound
  towards the eardrum, it contains wax secreting
  cells the wax traps dust etc.

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The Middle Ear

• Tympanic Membrane (Ear drum)a membrane that
  closes off entry into the middle ear vibrates
  when sound waves reach it.

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• Ossicles three small bones (Hammer, anvil and
  stirrup) that amplify the sound vibrations from
  the ear drum and carry them to the oval window.

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• Oval Window a small membrane that seperates the
  middle from the inner ear. Transmits vibrations
  from the ossicles to the inner ear.

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• Eustachian Tube a tube that connects the middle
  ear with the throat used to equalize pressure
  between the atmosphere and the middle ear.

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The Inner Ear

• Vestibule contains two small sacs called the
  Utricle and Saccule, aid in establishing head
  position. (Static Equilibrium)

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• Semicircular Canals 3 tubes arranged at
  different angles, filled with a fluid that helps
  in establishing body position (Dynamic
  Equilibrium)

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• Cochlea a snail shaped organ containing a fluid
  and specialized hair cells that move when
  vibrations from the oval window occur. The hair
  cells respond differently to sound waves of
  different frequencies and intensities.

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• Auditory Nerve transmits information to the
  brain from the inner ear on balance and sound.

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STEPS INVOLVED IN HEARING

• sound is a form of energy that travels in waves
• it is the movement of these waves that initiates
  the hearing process

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• 1.When sound waves reach your ear they push
  against the tympanic membrane causing it to
  vibrate.
• 2. The vibrations are transferred to the
  ossicles which concentrate and amplify the sound.

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• 3. The vibrations from the last bone, the
  stirrup, cause the movement of the Oval Window
  inwards
• 4. The movement of the window initiates movement
  of a fluid found within the Cochlea.

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• 5. This fluid movement stimulates the Basilar
  Membrane of the Organ of Corti the technical
  name given to the hearing apparatus in the
  Cochlea.

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• 6. Attached to the basilar membrane are Hair
  Cells that will bend in response to the
  stimulation.

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• 7. The bending hair cells stimulate sensory
  neurons that transmit the information through the
  Auditory Nerve to the Temporal Lobe of the
  Cerebrum.

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• Different Hair cells have different threshold
  levels that will depolarize depending on the
  frequency or intensity of the sound.

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Maintenance of Balance

• two components to balance

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1. Static Equilibrium

• balance involving the position or movement of the
  head.
• head position is determined by the two fluid
  filled sacs (Utricle and Saccule) found in the
  vestibule.

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• in the fluid are suspended particles called
  OTOLITHS.
• when the head moves, the otoliths moves this
  causes movement of the hair cells that line the
  interior of the sacs

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• the hair cells stimulate sensory neurons that
  carry information to the brain, through the
  auditory nerve, regarding head position

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2. Dynamic Equilibrium

• balance involving the movement of the body
• involves the movement of the fluid found in the
  SEMICIRCULAR CANALS

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• when we move, the fluid moves causing the
  movement of hair cells that line the canals.

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• when the hair cells move, they stimulate sensory
  neurons which will carry information regarding
  body position to the brain through the auditory
  nerve.