EFFECT OF ANOXEMIA, CARBON DIOXIDE AND LACTIC ACID ON ELECTRICAL PHENOMENA OF MYELINATED AND UNMYELINATED FIBRES OF THE AUTONOMIC NERVOUS SYSTEM

Abstract

The technique was in general similar to that used in the study of somatic nerve fibers, the nerve trunks being placed entirely within the gas chamber. As material, sciatic nerves of bullfrogs, cervical sympathetic and vagus trunks of the cat and turtle were generally used. For special purposes skin nerves of the cat and bullfrog, and Limu-lus nerves to the extremities were studied. Results indicate that the effect of anoxemia, CO2 and lactic acid on autonomic nerve fibers is in general similar to the effects of these agents on somatic nerve fibers. The threshold is ultimately raised and the conduction rate lessened. There is usually a marked preliminary lowering of threshold of unmyelinated fibers. The absolute refractory period is prolonged. Absolute refractoriness is a most convenient index of the nerve''s condition. Unmyelinated autonomic fibers are depressed more rapidly than myelinated autonomics. Somatic nerve fibers are less rapidly depressed than autonomic ones. The order of recovery in 0 is reversed. There is no indication of any change in the time relations of the spike of the axon action potential. It is lowered by anoxemia, pure CO2 and lactic acid. The retained portion of the potential is first increased by anoxemia and pure CO2 and weak lactic acid, and later decreased with the spike. It is also increased in depressed or injured nerves by 5% CO2. Both potentials finally disappear and reappear simultaneously. Since the recorded potential is in general the expression of a double lead from the nerve''s surface, differential depression of the action potential is inevitable because of the differential susceptibility of injured as compared with uninjured nerve. The possible effects of differential depression on the ballistically recorded action potential are discussed. The completely diphasic lead is the safest one for interpretation of the functions of nerve. The effects of fatigue on the recorded action potential are indicated. Treppe is not infrequently observed in depressed nerves.