> Corti's organ: Overview
Drawings: S. Blatrix - Pictures: M. Lenoir, R. Pujol
The organ of Corti is named after one of the first anatomists to give a detailed description (ref. a11) of the neuro-sensory cochlea. Seated on the basilar membrane, it is composed of the sensory cells, called hair cells, the neurons, and several types of support cells.
Schematic drawing of the organ of Corti
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In this schematic drawing from a transverse section of the basal turn of a mammalian cochlea, the two types of sensory cells: inner (IHC: 1) and outer hair cells (OHCs: 2) are seen on both sides of the tunnel of Corti (3) which is limited by the 2 pillars. The tectorial membrane (6), floating in endolymph, covers the hair cell, embedding the tips of the tallest OHC stereocilia. The IHC is surrounded by support cells while the OHCs are firmly "seated" on Deiters' cells (7), their lateral membrane being in direct contact with the corticolymph (almost identical to the perilymph) which fills in the tunnel of Corti (3) and the spaces of Nuel (8).The cuticular plate of hair cells, together with the head of pillars, the phalangeal processes of Deiters' cells and the apical membrane of other support cells, e.g. Hensen's cells (9), form the reticular lamina (5) sealing the endolymphatic compartment. Piercing the basilar membrane (4) at the habenula perforata (5), nerve fibres reach or leave the organ of Corti . |
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Function of the Corti's organ: schematic animated drawing
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Animation: S. Blatrix from a scientific concept by G. Rebillard and R. Pujol |
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For low and mid intensities sounds the function of the organ of Corti may be schematically summarised in 5 stages: (1) Sounds waves move the basilar membrane (BM) up and down. (2) Stereocilia of the OHCs , implanted in the tectorial membrane (TM), are bent and the cell is depolarised. (3) Excited (depolarised) OHCs react by contracting (= electromotility): this is an active mechanism. (4) Due to the tight coupling of OHCs with the BM and reticular lamina this active mechanism feeds energy back into the organ of Corti and IHCs are excited probably due to TM (Hensen's stripe) activation of stereocilia. (5) The IHC-auditory nerve synapse is activated and a message is sent to the CNS. |
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 M. Lenoir |
Both the surface of hair cells and the inside of the organ of Corti (at site of fracture) are seen. Lateral to the OHCs (blue arrows), remnants of the marginal net of the tectorial membrane (which has been removed) are visible. Green arrows point to fibers crossing the tunnel of Corti. |
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 M Lenoir |
Mid basal (bottom) and third (top) turns from a guinea pig cochlea are shown. Compare with SEM pictures below. |
 R Pujol |
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 M Lenoir |
After the stria and Reissner's membrane have been dissected out, the 3 turns of the spiralling basilar membrane supporting the organ of Corti can be seen here at low magnification. Frames point to higher magnifications (where hair cell surfaces are seen) at the base and apex of thecochlea. Scale bar: 2 mm
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 M Lenoir |
Hair cells pattern at the base of the cochlea (rat) Stereocilia from 1 row of inner hair cells (IHC) and 3 rows of outer hair cells (OHC) are visible, separated by the pillar cells. Scale bar: 15 µm |
 M. Lenoir |
Hair cells pattern at the apex of the cochlea (rat)
Same type of view as above. Note the increased lenght of stereocilia, as well as some disarray. |
 M. Lenoir |
Extreme apex of the same rat cochlea IHCs (uppermost row) stay properly arranged in one single row up to the extreme apex, except for the last two cells (arrow).
The distribution pattern of OHCs is greatly altered: 4 rows are seen in the right corner of the picture, but the organ of Corti ends (on the left) with 2, then 1 row of OHCs. |
 M. Lenoir |
Extreme apex of the mole-rat cochlea
Here, only the row of IHCs is seen, as though OHCs were not necessary for very low frequencies (below 20 Hz). |
