Hair bundle profiles along the chick basilar papilla

Cochlear hair cells play a central role in the transduction of sound into n eural output. Anatomical descriptions of these cells, and their protruding hair bundles, are of fundamental interest since hair cell transduction is d ependent on hair bundle micromechanics and hair bundle micromechanics depen ds on hair bundle morphology. In this paper, we describe quantitatively cha nges in the staircase profile of the hair bundle along the apical portion o f the chick's basilar papilla. Images of hair cells from 8 discretely disse cted segments of the apical 3rd of the basilar papilla were archived, and t he profile contour outlined by the tips of the stereocilia was digitised an d curves were fitted by linear and power equations. The hair bundles of tal l hair cells exhibited both linear and curvilinear profiles, which were equ ally distributed along the papilla. All short hair cells in our sample had straight contours. The differences in hair bundle shape among the tall hair cells may lead to differential susceptibility to injury and some variance in the current-displacement transduction curves due to differences in the t ranslation of forces throughout the hair bundle.