ELECTRIC POTENTIALS OCCURRING AROUND A NEURONE DURING ITS ANTIDROMIC ACTIVATION

Abstract

Potentials were recorded extracellularly around spinal moto-neurones, which were activated singly by stimulating small filaments of muscle nerve. At positions in the spinal cord where the response was large it had a complex time course, consisting of two negative components, signalling the separate activity of two parts of the motoneurone. On changing the position of recording, the first component was seen to attenuate rapidly with distance but did not change significantly in latency, whereas the second component did not attenuate so rapidly and showed a change in latency. The first component was attributed to activity of the soma, and the second to activity of the dendrites, which conduct at a rate of 0.7-1.0 m/sec. In addition similar potential waves were recorded around a border cell on stimulation of its axon. Comparison of potentials recorded intra- and extracellularly from the motoneurone indicates that the 30 mV step on the rising phase of the intracellular spike is produced by the soma, and the further rise to a peak of about 80 mV is produced by the dendrites. It is shown that no information on the passage of activity between soma and dendrites can be obtained from an analysis of potential fields occurring around a population of motoneurones.