Central arborization patterns of motor neurons innervating the antennular proximal segment ofCallinectes sapidus

Abstract

The three motor nerves innervating the muscles of the antennular proximal segment (PS) of the crab Callinectes sapidus were investigated using cobalt‐backfilling techniques. Filled soma were found ipsilaterally in the posterior medial cell nucleus (73 percent) and the ventral lateral cell nucleus (27 percent). Soma (diameters 10–50 μm) from both nuclei sent slender processes dorsally which arborized in optic neuropil, around the tegumentary nerve, beneath antennular fiber tract IIB (Sandeman and Okajima, 1973), and in lateral and medial antennular neuropils. Arborizations were ipsilateral with the exception of two projections in remotor nerve (25a) which connected regions of dorsal optic neuropil bilaterally. Potential deutocerebral sites of interaction between type IA and IB afferent fibers from antennular short‐hair sensilla (SHS) and PS motor neurons are discussed. Two neurons in promotor nerve (24a) are identified (PMa‐3 and PMa‐4) with processes in a section of the medial antennular neuropil known to...