Fig. 2

SBFSEM images of neuromast components.

(A) A low-power micrograph shows the general organization of a neuromast. The sensory organ lies between skeletal-muscle fibers, from which it is separated by the epithelial basal lamina, and the aqueous environment, into which the hair bundles protrude. The nuclei of hair cells form a layer above those of supporting cells. (B) The posterior lateral-line nerve (outlined in orange) contains two myelinated axons as well as numerous unmyelinated fibers. Seven afferent terminals, each denoted as ‘A’ and distinctively colored and numbered, arise as single branches of axons in the nerve and enter the neuromast through a pore in the epithelial basal lamina. One efferent axon labeled ‘E’ is also present. (C) The synaptic terminal of an efferent axon onto a hair cell displays a vesicle-filled bouton. Within the hair cell's cytoplasm lies a cistern that sequesters the Ca²⁺ that enters the cell during synaptic activity. (D) A perisynaptic compartment (outlined in orange) contains four afferent terminals, each denoted as ‘A’ and numbered, and a single efferent terminal labeled ‘E.’ The compartment is demarcated by two supporting cells. The hair cell makes an afferent synapse onto the axonal terminal A1. A synaptic ribbon in the hair cell is characterized by moderate electron density and a clear halo surrounded by synaptic vesicles. The ribbon is readily distinguished from the numerous mitochondria in all cell types. In each of the panels, the areas within some of the cellular contours delineated by annotators have been colored to emphasize specific cells or axonal terminals. In order to provide a broad color gamut, the scheme of coloration here is arbitrary and distinct from that in the other figures.