Peripheral fields and branching patterns of buccal mechanosensory neurons in the opisthobranch mollusc, Navanax inermis.

A population of about 75 primary sensory cells were identified on the dorsal surface of each buccal ganglion of Navanax. Each sensory cell possesses at least one mechanosensitive field in the pharyngeal wall or lips that correlates somatotopically with its position in the buccal ganglia. Many cells had additional fields that could be widely separated, requiring that their afferent processes branch. Cells were found with processes in more than one buccal nerve and with multiple processes in the same nerve. Hyperpolarization of the soma or repetitive electrical or physiological stimulation could cause failure of centripetal propagation of impulses. Impulses initiated in different branches could fail at different distances from the soma. Axon spikes that fail to invade the soma may or may not invade other branches. Axon spikes in separate branches that fail to invade the soma can summate to initiate an invading impulse. These findings suggest that integration of information from different branches may occur in a single sensory neuron.