THE POTENTIAL ANALYSIS OF THE TURTLE AND CAT SYMPATHETIC AND VAGUS NERVE TRUNKS

Abstract

In certain of these nerves, there are typically 4 action potential components designated as the A, B1, B2 and C elevations. In others, only the B1, B2 and C components are present, and in still others only the B2 and C, without, however, any prejudice as to homol-ogies of function in different nerves with similar potential forms. Each of these main components also exhibits secondary potential maxima. Threshold and conduction rates of the potential groups indicate the essential differences between the 4 potential components recognized. The fibers giving rise to the A and B1 elevations have a potential at the stimulus of short duration. Their chronaxie and absolutely refractory period are likewise short. In contrast the fibers giving rise to the B2 and C potentials have values 10 times as great for similar properties. Such evidence affords a means of differentiating axon types in nerve. Certain cervical sympathetic nerve trunks in the turtle exhibitonly the B2 and C potentials. A comparison of the histological picture of this type with that presenting 3 potential components, B1, B2 and C, affords a basis for the assignment of different nerve fiber types as origins of the various potential groups. The larger thinly myelinated axons give rise to the B1 component of potential; the smaller thinly myelinated axons contribute to the B2 potential; and the unmyelinated axons are the source of the C elevations in these nerves. The A elevation when present is assignable to the larger thickly myelinated axons. The B2 and C components of these nerves contain the autonomic motor fibers. The B1 component includes visceral afferent fibers.