Crash Course Hearing and Balance

• Sound creates vibrations in the air that beat against the eardrum, which pushes a series of tiny bones that move internal fluid against a membrane that triggers tiny hair cells -- which aren't actually hairs -- that stimulate neurons, which in turn send action potentials to the brain, which interprets them as sound
• The ear's vital role is maintaining your equilibrium
• Sound frequency


  The number of waves that pass a certain point at a given time
• Sound amplitude


  The difference between the high and low pressures created in the air by a sound wave
• How sound gets to the inner ear

  1. Sound waves caught by the pinna

  2. Funneled down the auditory canal

  3. Collide with the eardrum

  4. Vibrate the ossicles (hammer, anvil, stirrup)

  5. Vibrate the oval window fluid
• Middle ear


  • Amplifies sound waves so they are strong enough to move the fluid in the inner ear
• How the inner ear converts sound to electrical signals

  1. Basilar membrane vibrates

  2. Hair cells in the organ of Corti are triggered

  3. Graded potentials generated

  4. Action potentials sent to the brain via the auditory nerve
• Organ of Corti


  Structure in the cochlea with hair cells that convert vibrations to electrical signals
• Vestibular apparatus


  Structure in the inner ear that uses fluid movement and hair cells to detect head movement and maintain equilibrium
• How the vestibular apparatus detects head movement


  1. Fluid moves in the semicircular canals

  2. Hair cells detect fluid movement

  3. Action potentials sent to the brain
• The disconnect between vestibular and other senses of movement is why we get motion sickness