Audition Promenade round Cochlea autour Cochlée oreille ear organ of Corti oreille ear CRIC Montpellier Remy Pujol U254

	Hair cells
	Overview / Surface view / Stereocilia and Mechano-transduction
	Pictures : M. Lenoir

Scanning electron microscopy (SEM) allows a clear surface view of the hair cells and of their stereocilia tufts.

Cochlear spiral: rat cochlea

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 b ar: 2 mm

**SEM from basal turn of a rat cochlea**
M. Lenoir	M.Lenoir
The apical surface of inner support cells, one row of inner hair cells (i: IHCs), pillars of Corti (p), 3 rows of outer hair cells (o: OHCs) and Deiters' cells are visible. At the bottom the surface is fractured and the base of the 3rd row of OHCs is seen, as well as phalangeal processes of Deiters' cell (d). See an electronic zoom scale bar: 15 µm	The surface of the organ of Corti is seen at higher magnification and from the inner side so as to focus on the stereocilia pattern of both IHCs and OHCs (see details on high magnification pictures below). Also compare this very regular pattern with that observed at the apex. scale bar: 10 µm

Enlargements of IHC (left) and OHC (right) cuticular plates and stereocilia from rat basal turn
M. Lenoir	M. Lenoir
Almost linear arrangement of IHC stereocilia	"W" pattern of OHC stereocilia
In both cases 3 rows of stereocilia of graded length, linked to each other, are embedded in a glabrous(i.e. bearing no microvilli) cuticular plate (in contrast with the surface of supporting cells which bear numerous microvilli). scale bar: 3 µm

SEM from the apical turn of a rat cochlea

M. Lenoir

In comparison with the basal turn, apical hair cells, especially OHCs, have stereocilia that are much longer, less regularly organised and much more loosely linked to each other.

Frequently, as seen on the right, a 4th row of OHCs is observed.

See an electronic zoom

scale bar: 15 µm

Surface of apex of a guinea pig organ of Corti

M. Lenoir

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.

scale bar: 15 µm.

Extreme apex of a mole rat cochlea

M. Lenoi

This apical disorganisation is even more pronounced in 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).

scale bar: 15 µm