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• Ear

  Organ of hearing and balance
• 8th cranial nerve


  Cochlear part of the Vestibular Cochlear nerve, stimulated by vibrations caused by sound waves
• Except for ear pinna/auricle, the structures that form the ear are encased within the petrous portion of the temporal bone
• Ear

  • Made up of three main parts: external ear, middle ear and internal ear
• External ear

  • Consists of auricle/pinna and external acoustic meatus/auditory canal
• Auricle

  Made up of a skeleton of elastic cartilage and fibrous tissue, covered on both sides by a layer of skin
• Auricle


  • Cartilage is continuous with that of external acoustic meatus
  • Has an external surface facing laterally and an inner/cranial surface
  • Cartilage is curved so that several elevations and depressions are produced
  • Lowest part is soft, composed of a fold of skin with enclosed connective tissue - Lobule
  • Has a large depression at the center of the external surface - Concha
• External acoustic meatus


  Tube passing medially from the bottom of the concha of the auricle, closed medially by the tympanic membrane
• External acoustic meatus


  • Total length is approximately 24mm, with the outer 8mm being cartilaginous and the inner 16mm being bony
  • Has a narrowing at the junction of the cartilaginous and bony parts - Isthmus
  • Floor has a depression immediately lateral to the tympanic membrane where foreign bodies can get stuck
• Ceruminous glands


  Modified sweat glands in the skin lining the external acoustic meatus that secrete cerumen, a sticky material containing protective substances
• Movements of the temporomandibular joint during chewing and speaking massage the cartilaginous meatus, moving the wax towards the exterior
• Tympanic membrane (Eardrum)


  Oval shaped membrane that completely separates the external acoustic meatus from the middle ear, formed by three types of tissue: outer layer of hairless skin, middle layer of fibrous tissue, and inner layer of mucous membrane lining
• Middle ear


  Also known as tympanic cavity or tympanum, an irregular shaped air-filled cavity within the petrous portion of the temporal bone
• Middle ear


  • Separated from the external auditory canal by the tympanic membrane
  • Part of the cavity lies above the level of the tympanic membrane - Epitympanic recess
  • Cavity, contents and air sacs are lined with simple squamous or cuboidal epithelium
  • Lateral wall formed by temporal bone, roof and floor formed by temporal bone, posterior wall formed by temporal bone with openings leading to mastoid antrum, medial wall is a thin layer of temporal bone with oval and round windows
• Pharyngotympanic (Auditory or Eustachian) tube

  Extends from the nasopharynx to the middle ear cavity, about 4cm long and lined with ciliated columnar epithelium
• The presence of air at atmospheric pressure on both sides of the tympanic membrane is maintained by the pharyngotympanic tube, enabling the membrane to vibrate when sound waves strike it
• The eustachian tube is normally closed but is opened by swallowing or yawning when there is unequal pressure across the tympanic membrane
• Auditory ossicles


  • Malleus (lateral hammer shaped bone), Incus (middle anvil shaped bone), Stapes (medial stirrup shaped bone)
  • The three ossicles are held in position by fine ligaments
• Inner ear


  Made up of a complex system of cavities within the petrous temporal bone, consisting of the bony labyrinth and the membranous labyrinth
• Bony labyrinth


  • Cavity within the temporal bone lined with periosteum, made up of the vestibule, bony cochlea, and semicircular canals
  • Between the bony and membranous labyrinth there is a layer of watery fluid - Perilymph
  • Within the membranous labyrinth there is a watery fluid - Endolymph
• Vestibule


  Expanded part of the bony labyrinth nearest the middle ear, with the oval and round windows located in its lateral wall
• Bony cochlea


  • Continuous with the anterior part of the vestibule, a tube coiled on itself for two and three quarter turns, with a greater diameter at the basal turn and progressively narrower towards the apex
  • Has two compartments - Scala vestibuli (upper channel originating at the oval window) and Scala tympani (lower channel ending at the round window)
  • Partially separated by the spiral lamina, with the basilar membrane stretching from the free edge of the spiral lamina to the outer wall
• Organ of Corti


  Organ for sound reception resting on the basilar membrane within the duct of the cochlea
• Semicircular canals


  • Three tubes arranged in the three planes of space (anterior, posterior, lateral), continuous with the vestibule, with one end of each canal dilated - Ampulla
  • The anterior and posterior canals have a common channel - Crus commune, so the semicircular canals open into the vestibule through five openings
• Membranous labyrinth


  • Within the vestibule there are two rounded sacs - saccule (anterior) and utricle (posterior), connected by the utriculo-saccular duct
  • The part of the membranous labyrinth lying in the bony cochlea is the duct of the cochlea, containing the organ of Corti
  • Lying within each semicircular canal there is a semicircular duct, opening into the utricle
  • The saccus endolymphaticus is a blind pouch-like extension of the membranous labyrinth, communicating with the saccule and utricle