Microscopic structure of the membranous labyrinth-II

MICROSCOPIC STRUCTURE OF THE MEMBRANOUS LABYRINTH

  • The spiral organ of Corti: It is composed of a series of epithelial cells placed upon the basilar membrane projecting into the endolymph of cochlear duct. It extends through the entire length of the cochlear duct with the exception of a short distance at either end. Named in their order from within outwards the following specialized cell types comprise the organ of corti.
    • The border cells.
    • The inner hair cells.
    • The inner phalangeal cells.
    • The inner and outer pillar cells (inner and outer rods)
    • Outer phalangeal cells (cells of Dieters).
    • Outer hair cells.
    • Cells of Hensen.

Organ of corti

  • The Hensen cells are continuous with the cells of Claudius, which are cubical and extend over the remainder of the basilar membrane to the spiral ligament. All except the hair cells may be considered as sustentacular or supporting cells. The hair cells are intimately related to the endings of the cochlear nerve and are neuroepithelial cells.
  • 1. The border cells and cells of Hensen are slender columnar cells which rest on the basilar membrane and are arranged in the inner and outer aspects of the hair cells.
  • 2. The hair cells are columnar cells. The free surface of each has short stiff hairs, which are in contact with the tectorial membrane. Their rounded basal ends rest on the phalangeal cells. The inner hair cells form a single row while the outer hair cells are arranged from 3 rows in the basal coil to 5 rows in the apical coil. The hair cell is arranged on either side of the inner and outer pillar cells or rods of corti.
  • 3. The phalangeal cells are arranged below the hair cells in corresponding number of rows. Their bases rest on the basilar membrane and their upper borders are concave and on these rest the lower ends of hair cells. The nucleus is located in the basal part of the cells and from the upper part of the cell a slender process passes between the hair cells to the surface and ends in a cuticular plate.
  • 4. The pillar cells or rods of Corti: These are inner and outer rods or pillar cells and are modified columnar cells with a broad basal part with nucleus rests on the basilar membrane and an elongated body or pillar, which ends at the free upper extremity in an enlarged head. The bases of the inner and outer pillar cells are farther apart but their heads converge and articulate with each other. Thus a triangular tunnel of Corti is formed between the two pillar cells and the basilar membrane.
  • Tectorial membrane: Above the cells of the organ of corti and lying in contact with the hair cells in life is a thick, elongated gelatinous structure called the tectorial membrane. It is usually distorted during fixation. It begins at the inner angle of the cochlear duct as a thin layer attached to the epithelial surface on the thickened periosteum over the osseous spiral lamina (limbus spiralis). Farther outward, the membrane becomes thicker with a pronounced convexity on its upper surface and its lower surface is in contact with hair cells of the organ of corti. Beyond this, it becomes thinner and ends in a rounded tip.
  • Nerve fibres : The peripheral processes of the bipolar cells of the spiral ganglion, pass through the tympanic lip of the spiral lamina and reach the organ of corti. Some of the fibres end on the inner hair cells, while others pass across the tunnel of corti and end on the outer hair cells. The nerve fibres form fine plexuses around the bases of the hair cells and terminate on button like endings in contact with the surfaces of hair cells.
  • Functions
  • Cochlea: The organ of corti in the cochlea is the receptor for the sense of hearing. Vibrations transmitted from the tympanic membrane through the chain of auditory ossicles reach the fenestra ovalis and perilymph. It is believed that the vibrations of the basilar membrane caused by those in perilymph stimulate the hair cells. The vibrating hair cells are in contact with the tectorial membrane through their hairs. The stimuli are conveyed through the spiral ganglion and the eighth cranial nerve to the brain. (For further pathways see neurology)
  • Vestibule : The receptors in the macula utriculi and crista ampullaris are stimulated by alterations of the position of head and the impulses (equilibrator or vestibular) are concerned with the maintenance of equilibrium of the body under various conditions.
Last modified: Monday, 17 October 2011, 7:27 AM