The attachment of the spiral ligament to the cochlear wall: anchoring cells and the creation of tension.

The spiral ligament of the cochlea contains an array of criss-crossing extracellular fibers which are anchored to the bony wall of the cochlea and into the outer margin of the basilar membrane. In certain areas there is an accumulation of unusual sponge-shaped cells which are clearly involved in anchoring the extracellular fibers to the bony wall and possibly in maintaining or applying radial tension on the spiral ligament-basilar membrane complex. The latter is suggested by the occurrence of a large number of intracellular fibers which have many of the characteristics of the so-called 'stress fibers' of cultured fibroblasts. Where these cells occur the fibers of the spiral ligament bend sharply, presumably due to tension applied on them. This paper provides transmission and scanning electron micrographs of the 'anchoring' cells in the mouse and two species of bats. In the horseshoe bat, the anchoring cells provide the sole mode of attachment of most of the spiral ligament to the otic capsule. Marked differences occur not only among species but also in different regions of the spiral ligament. A diagram is provided to show how the system of cells and fibers might create or maintain tension on the basilar membrane.