The Internal Ear

  • Consists of cavities and canals filled with perilymp = bony labyrinth
  • It also contains sacs and tubes filled with endolymph = membranous labyrinth
  • The membranous labyrinth is located in the body labyrinth and is attached to it via connective tissue strands or thickenings of periosteum.
Fig. 12.1 Anatomy of the ear

Stevens and Lowe p.187

Bony Labyrinth

  • The oval window leads to the vestibule
  • Six openings are found in the vestibule:
    1. posterior 5 for semicircular canals
    2. anterior one for cochlea
  • The bony labyrinth is lined with a layer of squamous epithelium resting on a thin lamina propria that is fused with the periosteum

Membranous Labyrinth

  • Consists of two sacks:
    1. the smaller anterior saccule
    2. larger posterior utricle
  • These two sacks are joined via the two short legs of a Y-shaped tube
  • The long leg of the Y is formed by the endolymphatic duct
  • The cochlear duct emerges from the anterior side of the saccule and the semicircular canals emerge from the posterior side of the utricle

Cochlea and Cochlear Duct

The cochlear duct has 3 walls:
  1. 1. Lower wall
    • Formed by the basilar membrane that extends from the edge of the osseous spiral lamina to the outer wall
    • The organ of Corti is located on this membrane
  2. 2. Upper wall
    • Formed by the vestibular/Reissner's membrane thar extands from the spiral limbus to the outer wall
  3. 3. Outer wall
    • Formed by the spiral ligament and specialised epithelium

Microscopic Structures of the Cochlear Duct

Vestibular membrane

  • Extremely thin
  • Consists of two layers of epithelial cells with a small amount of connective tissue inbetween
Fig. 12.4 Cochlea

Stevens and Lowe p. 190

Spiral Ligament

Stria Vascularis

Spiral Organ of Corti

Fig. 12.5 Organ of Corti

Stevens and Lowe p.191

Fig. 24.17 Photomicrograph of the vestibular duct and spiral organ of Corti

Ross et al. p832

The Basilar membrane

- Two sections:
  1. 1. Pars arcuata - thin and contains blood vessels
  2. 2. Pars pectinata - contains no blood vessels

Utricle, Saccule and Semi-circular canals

  • - The walls of these structures are thin and consists of vascular connective tissue
  • - On the inside the connective tissue is lined with a layer of squamous or cuboidal epithelium
  • - On the lateral wall of the utricle and medial wall of the saccule, a thickening of the inner wall occurs - the maculae
  • - In the ampullae of the semicircular canals are transverse ridges - cristae ampullares
  • - The macule and cristae are called the vestibular organ because they register equilibrium.

Fig. 24.21 Structure of the maculae

Junqueira and Carneiro p. 484

Fig. 24.23 Crista ampullaris

Junqueira and Carneiro p. 485

Steps involved in hearing speech
Sound signals travel from the ear to the brain where they are recognized and decoded

Public domain: Zina Deretsky, National Science Foundation


© maart 2001 - julie 2007 marius loots