AN ANALYSIS OF POTENTIALS RECORDED INTRACELLULARLY FROM THE SPINAL GANGLION CELL

Abstract

1. The spike potentials were recorded intracellularly from spinal ganglion cells of toads and they were analysed by using the hyperpolarisation.
2. The intracellular action potential of the spinal ganglion cell had two inflections, which is attributed to successive initiation of three component spikes, the S, NM and M spikes.
3. The magnitude of the S spike and that of the second inflection increased with the increase of the membrane potential along lines having a slope of unity. This indicates that the S spike is generated from the cell body.
4. The magnitude of the NM spike as well as that of the first inflection showed a linear increase with the slope smaller than unity, by which the NM spike is attributed to the non-myelinated segment.
5. The critical depolarisation for initiating the NM spike was 15 mV, while that for initiating the S spike was 45 mV. This difference should be due to the membrane properties of the non-myelinated segment and the cell body.
6. The potential spread along the axon of the ganglion cell was estimated. The spike potential generated from the myelinated axon had an attenuation factor of 0.2-0.6 for its electrotonic spread to the non-myelinated segment and 0.3-0.8 for the further spread to the cell body. The spike potential generated from the non-myelinated segment spreads to the cell body by a factor larger than 0.5.
7. The hyperpolarised potential as well as the depolarised one spread electrotonically to the non-myelinated segment without suffering from attenuation. The former also extended to the site of the M spike generation decreasing by a factor of 0.5-1.0.
8. The critical hyperpolarisation for blocking the M-NM and NM-S conductions and their safety factors were estimated with suitable assumptions.