Some electrical measurements of motoneuron parameters

Electrical properties of the membrane of cat spinal motoneurons have been studied using pulses of current and sinusoidally varying currents applied with intracellular microelectrodes. Hyperpolarization of the motoneuron membrane produces time and voltage dependent changes in membrane resistance and E. M. F. The voltage transients produced by steps of current have been analyzed in order to determine the effective electrotonic length of the dendrites. In a sample of 16 motoneurons, the average total length of the dendrites was 1.5 times the electrotonic length constant of the dendrites. The phase relationship between applied sinusoidal currents and the resultant transmembrane voltage was studied to determine the dendritic to somatic conductance ratio, rho. In a sample of seven cells the best estimate for rho was in the range between 5 and 10.