On the basilar membrane are 4 rows of sensory receptor cells called hair cells: 1 row of inner hair cells and 3 rows of outer hair cells, Each hair cell is separated by several supporting cells. Hair cells are so called because of fine apical protrusions called stereocilia. Outer Hair Cells stereocilia Outer Efferent hair cells nel axons of cort Inner hair Cells Supporting cellsOn the basilar membrane are 4 rows of sensory receptor cells called hair cells: 1 row of inner hair cells and 3 rows of outer hair cells. Each hair cell is separated by several supporting cells. Hair cells are so- called because of fine apical protrusions called stereocilia. Outer Hair Cells Inner Hair Cells Supporting cells. stereocilia