I. Hearing and Equilibrium : EARS

• Parts of the Ear:

  External ear is pinna or auricle
• Parts of the Ear:

  External ear is external acoustic meatus
• Parts of the Ear:

  Middle ear is also known as tympanic cavity
• Parts of the Ear:

  Middle ear is ossicles (malleus, incus, stapes)
• Parts of the Ear:

  Internal ear is also known as Labyrinth
• External ear:

  Pinna or auricle - shell shaped structure surrounding the auditory canal opening
• External ear:

  External auditory canal -= a short narrow chamber (about 1 inch long by ½ inch wide)
• External ear:

  External auditory canal -Curved into temporal bone of the skull
• External ear:

  Tympanic membrane or eardrum -a thin membrane separating outer from middle ear
• Middle ear:

  Malleus (hammer)- attached to tympanic membrane
• Middle ear:

  Incus also known as anvil
• Middle ear:

  Stapes (stirrups)-presses on the oval window of the inner ear
• Middle ear a a small, air-filled cavity within the temporal bone
• Internal ear:

  Bony Labyrinth - wall is bony-temporal bone
• Internal ear:

  Bony Labyrinth - fluid inside is perilymph
• Internal ear:

  Cochlea- made up of scala vestibuli and tympani
• Internal ear:

  Cochlea- concerned with hearing
• Internal ear:

  Vestibule- concerned with static equilibrium
• Internal ear:

  3 Semicircular canals- involved in circular/dynamic equilibrium
• Internal ear located in petrous part of temporal bone
• PARTS of Internal ear:

  • cochlear duct (scala media) located within bony cochlea contains receptors for hearing : ORGAN OF CORTI
  • semicircular ducts (located within semicircular canals)
  • utricle and saccule (located within vestibule)
  • semicircular ducts, utricle and saccule contain vestibular receptors ( Equilibrium or Balance )
• Membranous labyrinth- vestibular organs for equilibrium and balance
• Organs of Equilibrium

  1. Vestibule
  2. Semicircular canals
• Vestibular maculae: Haircells – sensory mechanoreceptor
• Cochlea : Hearing specifically
• Deafness- hearing loss
• Weber’s test- base of vibrating fork is applied to the forehead in the midline
• Rinne’s test - base of tuning fork over mastoid; can no longer be heard, held in front of ear
• Weber's test

  • Normal – sound at midline
  • Conduction – louder on affected ear
  • Sensorineural – louder in normal
• Rinne's test

  • Normal – AC > BC
  • Conduction – BC > AC
  • Sensorineural - both diminished but AC > BC
• Auditory center: BA 41,42
• auricle is the fleshy part of the external ear on the outside of the head
• external auditory canal is passageway that leads to the eardrum
• bony labyrinth is interconnecting tunnels and chambers within temporal bone
• membranous labyrinth is smaller set of membranous tunnel and chambers
• perilymph is space bet. membranous and bony labyrinth
• endolymph is a clear fluid
• cochlea is like a snail shell
• 2 major steps of process of hearing:

  1. conduction of sound waves
  2. stimulation of hearing receptors
• conduction involves structures of the outer, middle and inner ears