248
i k E FLOCK
vated by two myelinated nerve fibers which are afferent and a few thin
myelinated nerve fibers which carry efferent impulses. Physiologically
one whole stitch serves as one functional unit rather than the individual
neuromast since each nerve fiber branches in a tram-line fashion to
contact all neuromasts within the stitch.
The sensory hair bundle springing from each hair cells contains about
15 stereocilia and a single kinocilium. The stereocilia are somewhat less
well developed than in canal organs, they are not arranged in the same
orderly fashion, and their height is less. Within each neuromast neighboring hair cells also face opposite directions, along the axis of the stitch.
111. SENSORY EXCITATION IN THE HAIR CELL
When the hair cell is mechanically excited by cupula displacement
electric potential changes occur inside the cell. This response, the
receptor potential, can be recorded with intracellular microelectrodes as
Fig. 7. Three epidermal neuromasts of Necturus maculosus occupy the bottom
of a shallow ditch. From each organ a fragile cupula extends. “Mulberry” cells are
supeficial cells of the epidermis.