an important organ that contains the sensory cells essential to hearing; found on the upper or vestibular surface of the basilar membrane
What is the organ of Corti composed of?
mostly epithelial structures that occupy the length and breadth of the basilar membrane
What two classifications can the cells of the organ of Corti fall into?
receptive or supportive cells
rods of Corti
supportive cells that are widely separated at their bases and converge to meet at the top; near the osseous spiral lamina
What is the floor of the tunnel of Corti formed by?
the bases of the pillar cells and by the basilar membrane
inner hair cells
single row of cells flanked on inner side by supportive cells; found on modiolar side of the inner pillar cells
outer hair cells
three rows of cells held in position at bases and tops by a complex network of cells
How does the surface of the vestibular lip appear from the vestibular surface (above)?
it is covered with a distinctive layer of epithelium; cells are arranged in parallel rows; when viewed from above, they appear as "auditory teeth", or serrated
location where the main body of the phalangeal cells rest directly on the spiral lamina
rigid process which is an extension of the phalangeal cell; extends upward to the level of the hair cell
Where do the inner rods of Corti rest?
at the point of junction of the tympnaic lip of the osseous spiral lamina and the basilar membrane
Where do the outer rods of Corti rest?
base rests on the outer limit of the arcuate zone of the basilar membrane
How does the distance between the inner and outer rods change as they move through the cochlea?
distance between bases increases from the basal end to the apex of the cochlea, while the angles between the rods and the basilar membrane diminishes
Are the walls of the inner tunnel of COrti solid?
no; they have slit-like spaces found between the rods which permit endolymph to circulate and nerve fibers to pass through as they course toward the modiolus and the nerve cell bodies
thin headplates of the outer pillar cells which bridge a gap between the inner hair cells and the first row of outer hair cells
delicate netlike structure which lies over spiral organ; formed from the thin headplates that unite with the phalangeal processes of other supporting cells
cells of Deiters
in direct contact with the bases of the outer pillars; similar to the inner phalangeal cells
space of Nuel
inverted triangular endolymphatic space; formed by main bodies of phalangeal cells- bodies become widely separated above
What is unique about the main body of the Deiters cell?
main body is cylindrical; its shape modifies to form a cup that snugly accomodates the basal end of an outer hair cell
What is the reticular membrane composed of?
inner phalanges, headplates of the inner rods, phalangeal processes of the outer rods and of the Deiters cells; not an independent structure
What is the function of the reticular membrane?
lend support to the apexes of the hair cells whose tufts of cilia occupy the spaces in the netlike matrix and project beyond it toward the tectorial membrane
formed by the space made between the apex of the cells of Henson and the outer row of hair cells
Cells of Claudius and Boettcher
rows of columnar and cuboidal cells that decrease in height and lie outside Hensen's cells; continuous with a highly vascular layer of epithelium lining the spiral ligament
probably secretes endolymph which is a nutritive function vital to hearing, since the spiral organ does not have a blood supply; has been likened to a microkidney; also believed to be a source of a positive 80 mV DC endolymphatic resting potentional
How are the inner and outer hair cells different?
in shape, in arrangements of hairs or stereocilia, and in nerve supply
found at upper extremity of the inner hair cell; oval-shaped upper extremity is capped by the cuticle
single large hair found on upper free surface of all sensory and supportive cells during embryonic development; disappears in latter fetal life; in adults is a structure called basal body
structure developing from kinocilium found during embryonic stage; surrounded by aggregate of granular material
How many inner hair cells are found along the basilar membrane?
about 80 inner hair cels per mm at basal end and 115 cells per mm at apical end
apex of inner hair cell
cuticle capped upper part of inner hair cell; slightly concave; has about 48 stereocilia
How are the stereocilia arranged on the apex of the inner hair cell?
in three or four wavy rows; oriented parallel to the longitudinal axis of the cochlea
WHat are the physical properties of the stereocilia?
larger in diameter at upper free ends, and outer row of cilia are the longest; length increases from base to apex and stereocilia of inner cells are coarser than those of outer hair cells
How do cilia act together?
they are joined by bridges of very fine fibrils so that all cilia on one cell tend to move together as a unit when the longest one is bent
How are the stereocilia connected?
sideways by links that run parallel to the cuticular plate; lins run between the stereocilia of the same row as well as between stereocilia of different rows
What is the result of these stereocilia connections?
Possibly excitation with stretching and inhibition with relaxation
What surrounds the entire hair cell?
plasma membrane; cytoplasm of inner cells is particularly rich in endoplasmic reticulum and in mitochondria, especially in apical region
What features do the outer hair cells share with inner hair cells?
capped with cuticular membrane form which a number of stereocilia protrude, rising above reticular membrane; contain a basal body; and entire cell and its cilia are covered with well-defined plasma membrane
What are the shape of outer hair cells?
cyclindrical, with rounded nucleated base that nestles snugly into cup-shaped head of the Deiters cells
How does the arrangement of the outer hair cells differ from that of the inner hair cells?
distributed in three or more rows, in form of letter V or W with the base of the W directed towards the spiral lamina
What implications does the length of the stereocilia have?
suggests that they respond primarily to a lateral (radial) shearing movement
Explain the number and distribution of the outer hair cell bodies
length increases from about 20 microns basally to about 50 microns apically, but at same time the number of stereocilia decreases from about 130 per cell basally to about 65 to 70 in the apical turn
What is the current estimated number of hair cells?
about 3500 inner hair cells and about 12,000 to 20,000 outer hair cells- probably closer to the conservative number
delicate structure connected to the epithelial covering of the vestibular lip of the limbus
How would you describe the physical characteristics of the tectorial membrane?
semitransparent, gelatinous structure, with a density scarcely exceeding that of endolymph
What are the three separate substrata of the tectorial membrane?
cover net, fibrous main body, homogeneous basal layer (Hardesty's membrane),