Figure 3.

Most of the ChAT-positive fibers in the osseous spiral lamina are unmyelinated. A, B, These images from two confocal z-stacks are both from a 78-year-old male. In each cochlear frequency region (A, 0.35 kHz; B, 4.0 kHz), a maximum projection in the xy plane is shown, along with selected xz and zy slices, positioned as indicated by the dashed yellow lines. Black-filled arrowheads in both xy projections point to the spiraling bundles of efferent fibers. Arrowhead in A zy points to a spiraling myelinated efferent (ChAT-positive) axon, while the arrowhead in A xz points to the unmyelinated radially directed portion of an efferent axon. Scale bar and orientation arrows in B apply to A. The x arrows point along the spiral toward the base, y arrows point radially toward the organ of Corti, and z arrows point toward scala tympani. NF, neurofilament.