THE ELECTRICAL ACTIVITIES OF SINGLE MOTONEURONES IN TOAD'S SPINAL CORD, RECORDED WITH INTRACELLULAR ELECTRODES

Abstract

1. By inserting glass micro-electrodes, whose external tip diameter was less than 1μ, into ventral horn cells in excised toad's spinal cord, the resting membrane potential and the action potential of single motoneurones were recorded.2. In response to a single stimulus delivered to a dorsal root, there appeared firstly synaptic potentials in a motoneurone, which brought about spike potentials when they attained a certain size by summation. Positive synaptic potentials were encountered occasionally.3. When stimulated antidromically by the impulses in ventral root fibers, the motoneurone responded with a slow negative potential which resembled the synaptic potential, followed by a spike potential of soma.4. The spike potential was followed by a negative after-potential and then by a positive after-potential whose relative size was much greater than that of the axon.5. Some motoneurones showed repetitive spike discharges for a short time immediately after the insertion of the micro-electrode. In these cases cyclic changes of the base-line potential were observed coincidentally with the period of spike discharge.6. Activities of cells which were supposed to be internuncial neurones were also recorded.7. The effects of constant currents flowing through motoneurones on the resting and action potentials were tested. It was found that the spike potentials were more sensitive to polarizing currents than synaptic and resting potentials.