Motor innervation of the pharynx levator muscle of the snail, Helix pomatia: physiological and histological properties.

(1) Motor innervation of the pharynx levator muscle of Helix pomatia was investigated with intracellular recording and axonal iontophoresis of cobalt chloride. (2) Muscle fibers respond to direct electrical stimulation of the muscle with active graded responses or non-overshooting spike potentials. (3) Each fiber is innervated via the external and internal lip nerves by several (mostly 3) excitatory nerve fibers each. Two types of EPSPs can be distinguished according to amplitude, duration, and facilitation. (4) Axonal CoCl2-staining via an external lip nerve branch revealed many nerve fibers entering the muscle and branching there into a rich network of blebbed fibers of various diameters.