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

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