Smooth Muscle: Autonomic Nerve Transmission

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Abstract
Transmission of excitation from autonomic nerves to smooth muscle is essentially similar to that found at other neuromuscular junctions. It is possible that, unlike other known neuroeffector junctions, the axons passing close to muscle fibers release transmitter substances at intervals along their length and do not possess many discrete endings at all. This could account for the diffuse influence of autonomic nerve fibers on smooth muscle and the apparent density of its innervation. Electrophysiological observations of the action of transmitter substances at the membrane level suggest that the smooth muscle membrane has many properties in common with the end plate regions of skeletal muscle; for example, Ach increases the permeability of the membrane to sodium, potassium, and probably other ions. It is suggested that a combination of quantitative assay, electron microscopy, fluorescent staining of catecholamines, differential isolation of transmitters, and micro-electrode studies on autonomic nerve-smooth muscle preparations is beginning, and will continue, to clarify the nature of the autonomic transmission process which has for so long remained a mystery. 225 references.