Ear

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Ear

• Composed of 3 parts
• a) external ear
• b) middle ear
• c) inner ear
• Includes organs of balance and hearing.

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External Ear

• a) auricle (pinna) - elastic cartilage plate
  covered with skin few slips of skeletal muscle
  provide movement.
• b) external auditory meatus - firm oval tube
  outer 1/3 of elastic cartilage inner 2/3's of
  bone lined with thick skin with many modified
  sweat glands wax glands Ceruminous glands,
  hair follicles
• c) tympanic membrane (ear drum) core of DICT
  in two layers skin on outer surface mucosa of
  simple squamous - cuboidal epithelium on inside.

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Middle Ear

• Tympanic cavity lined with simple
  cuboidal-squamous epithelium opens into
  oro-nasal pharynx by auditory tube (Eustachian
  Tube)
• Three bones (auditory ossicles) suspended from
  the roof by tiny ligaments.
• Malleus attaches to inner margin of ear drum
• Incus is the middle ossicle
• Stapes attaches to a membrane covered opening
  (oval window) into the cochlea.

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Internal Ear

• System of bone canals ( Bony Labyrinth) and
  membrane lined cavities (Membranous Labyrinth).
• Bony Labyrinth cavities filled with perilymph -
  fluid similar to CSF - and connects via scala
  tympani to arachnoid space.
• Membranous Labyrinth is filled with endolymph -
  more like intracellular fluids (high in K).

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Balance

• Three semicircular canals and vestibule of outer
  utricle and inner saccule bony labyrinth.
• Membranous labyrinth inside bony is of DICT
  supporting tissue lined with simple squamous
  epithelium simple squamous is replaced by
  neuroepithelium periodically

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Balance

• Balance Receptor Organs at ends of semicircular
  canals in expanded regions (Ampullae) organ
  inside is Crista Ampullaris.
• Simple columnar epithelium sensory hair cells
  (neuroepithelium) and supporting simple columnar
  epithelium Sustentacular cells.
• Supporting cells secrete mucoid cupula on tops of
  hair cells.

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Balance

• In vestibule, receptor organs (Maculae)
• Macula Utriculus lateral wall of utricle
• Macula Sacculus floor of saccule
• Hair cells covered with gelatinous layer and
  otoliths (CaCO3 salt crystals) Otoconia.

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Hearing

• Sound Receptor Organ
• Cochlea auditory part of bony labyrinth
• - a spiral bony tube coiling 2 ½ turns tube
  wraps around a central bony core (Modiolus).
• Bony labyrinth divides perilymph cylinder into
  two tubes.
• Upper Scala Vestibuli
• Lower Scala Tympani. Membranous labyrinth
  forms the central tube Scala Media.

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Hearing

• Modiolus forms a spiral shelf Osseous Spiral
  Lamina - contributes to formation of floor of
  Scala Media.
• Covered with DICT Spiral Limbus.
• Outer margin of Scala Media is thickened
  periosteum Spiral Ligament.
• Roof of Scala Media is the Vestibular Membrane
  Separates Scala Vestibuli from the Scala Media.
• Vestibular Membrane is of delicate areolar CT
  with simple squamous epithelium on both sides.

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Hearing

• The floor of the Scala Media is the Basilar
  Membrane - a ribbon of dense fibrous CT (DICT)
  with many neurons covered with cuboidal to
  columnar epith.
• (neuroepithelium Organ of Corti) on the Scala
  Media side and simple squamous epith. on the
  tympani side.
• Hair cells of the Organ of Corti are embedded in
  a mucoid body Tectorial Membrane.
• Outer wall of Scala Media is of vascularized
  epith.
• (pseudostrat. columnar) Stria Vascularis
• May secretes endolymph and regulate its
  concentrations.

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Hearing

• Ganglion cells of Cochlear Branch of Cranial VIII
  lie in the modiolus as the Spiral Ganglion.
• Perilymph of the vestibuli and tympani connect at
  the top of the cochlea via Helicotrema.
• Scala vestibuli connects to the middle ear via
  the oval window.
• Scala tympani connects to the middle ear via the
  Fenestra Rotundi round window