Hearing and Balance

External ear (hearing)
1. Auricle
  1. Fleshy part
  2. Elastic cartilage covered in skin
  3. Shape directs soundwave to external auditory canal
2. External auditory canal
  1. Lined with hairs
  2. Ceruminous glands
    1. Cerumen - modified sebum (earwax)
  3. Hairs + cerumen prevent foreign bodies reaching tympanic membrane
3. Tympanic membrane
  1. Thin, semitransparent and nearly oval shape
  2. Seprates external and middle ear
  3. 3 layers
    1. Simple cubodial epithelium (inner surface)
    2. Thin stratified columnar epithelium (outer surface)
    3. Connective tissue (middle)
  4. Soundwaves cause it to vibrate
  5. Rupture lead to hearing impairment
Inner ear (hearing and balance)
1. Sensory
2. Interconnecting, fluid-filled tunnels and chambers (within the petrous portion of temporal bone)
3. Bony labyrinth within the temporal bone
  1. Lined with endosteum
    1. Inner surface endosteum lined with perilymphatic cells
  2. Membranous labyrinth
    1. Outer surface of membranous labyrinth lined with perilymphatic cells
    2. Filled with fluid - endolmyph
      1. High [K+] and low [Na+] opposite of perilymph concentrations
  3. Space between bony and membranous labryinth filled with perilymph
  4. 3 regions
    1. Cochlea
      1. 3 parts of membranous labyrinth
        Scala Vestibuli
        Extends from oval window to helicotrema, back from apex, parallel to scala vestibuli to membrane of round window
        Scala Tympani
        Cochlear duct
    2. Vestibule
      1. Balance
    3. Semicircular canals
      1. Balance
Middle ear (hearing)
1. Air-filled space (within the petrous portion of the temporal bone)
  1. 3 Auditory ossicles
    1. Malleus
      1. Vibration of tympanic membrane causes malleus to vibrate because malleus handle attachted to inner surface of tymoanic membrane
      2. Malleus head attached by very small synovial joint to incus
    2. Incus
      1. Incus synovial joint with malleus and synovial joint with stapes
    3. Stapes
      1. Foot plate fits into oval window and held by flexible annular ligament
    4. Transmit vibrations from tympanic membrane to oval window
    5. 2 small skeletal muscles insert into auditory ossicles
      1. Tensor Tympani attached to malleus and innervated by trigeminal nerve (V)
      2. Stapedius muscle attached to stapes and innervated by facial nerve (VII)
2. 4 openings
  1. 2 covered openings
    1. Round and oval on Medial side
    2. Seperate from inner ear
  2. 2 additional openings
    1. Opens into mastoid air cells
    2. Auditory tube (pharyngotympanic tube)
      1. opens into pharynx
      2. Equalizes air pressure of outside air and middle ear cavity
        Unequal pressure can distort tympanic plate, dampens its vibrations, associated pain fibres stimulated

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Hearing and Balance

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	Created by Colleen Curley almost 9 years ago