Explain the functions and parts of the ear.

Functions of the Ears

• Hearing
• Maintenance of body balance

Anatomy of the Ear

• Divided into three major sections:

  • Outer ear
  • Middle ear
  • Inner ear
    

• Outer ear = Pinna + External auditory meatus (Canal)

  • Pinna − collects the vibrations that produce sound
  • Canal − leads inwards and extends up to the tympanic membrane (Ear drum)
  • Wax-secreting sebaceous glands are present in the skin of the pinna and the canal.

• Middle ear: Has 3 ossicles (Malleus, Incus, Stapes)

  • Malleus is attached to the ear drum and stapes is attached to the oval window of the cochlea. Middle ear communicates to the inner ear through the oval window.
  • Ossicles increase efficiency of transmission of sound waves to the inner ear.
  • Eustachian tube − connects the middle ear cavity with the pharynx; equalises the pressure on either sides of the ear drum

• Inner ear (labyrinth): Has 2 parts (Bony Labyrinth and Membranous Labyrinth)

  • Bony Labyrinth − series of channels in which the membranous labyrinth lies
  • Membranous Labyrinth − surrounded by a fluid called perilymph and filled with a fluid called endolymph

  • Cochlea − coiled portion of the labyrinth

    • 2 membranes surround cochlea, the reissner's membrane and the basilar membrane.
    • These membranes divide the bony labyrinth into 3 parts -upper scala vestibuli, middle scala media and lower scala tympani.
  • Scala media − filled with endolymph
  • Scala vestibuli − ends at the oval window
    Scala tympani − ends at the round window that opens to the middle ear
  • Organ of Corti − located on the basilar membrane and contains auditory receptors called hair cells (close contact with afferent nerve fibres)
  • Tectorial membrane − elastic membrane present above the rows of hair cells
    
  • Vestibular apparatus: Complex system located above the cochlea
  • Composition − 3 semi-circular canals and otolith organ (has saccule and utricle)
  • Base of the canals is swollen to form ampulla, which contains a projecting ridge called the crista ampullaris; it has hair cells
  • Saccule and utricle − contain macula, which along with crista is responsible for maintaining the balance of the body and posture