Hearing

• The functions of the ear are hearing and balance. They involve the activation of mechanoreceptors called hair cells.
• The ear is divided into the external, middle and inner ear
• External ear

  • auricle (pinna): visible portion of the ear
  • external auditory canal: tube leading from the auricle and ending at the tympanic membrane
• Middle ear

  • auditory tube (eustachian tubes)
  • 3 auditory ossicles
• The auditory tube connects the middle ear with the upper part of the throat. When open, it allows air pressure to equalize
• Auditory ossicles

  • malleus (hammer): attached to the inner surface of the tympanic membrane
  • incus (anvil): attached to the malleus and stapes
  • stapes (stirrup): attached to the incus
• Inner ear

  • cochlea: hearing
  • vestibule: balance
  • semicircular canals: balance
• Endolymph is a clear, potassium rich fluid filling the inside of these structures
• Mechanism of hearing

  • sound waves in air move through auditory canal
  • tympanic membrane creates ossicle movement and the stapes strikes the oval window
  • pressures waves from the oval window travel in perilymph along the scala vestibuli to the scala tympani
  • pressure waves in endolymph cause hair cells to bend against tectorial membrane
  • neurotransmitter is released and a signal is sent to the sensory neurons
• Pitch is registered by which hairs in the cochlea are stimulated (a higher note is further down the cochlea)
• Volume is registered by the intensity of the sound waves (larger vibrations = louder)
• Cochlear sensory neurons leave the ear and ascend to the brain the primary auditory area in the temporal lobe of the cerebral cortex