Activation of gracile nucleus: time distribution of activity in presynaptic and postsynaptic elements.

Abstract The time required for impulse conduction from the skin to the gracile nucleus has been determined for primary afferent fibers in the sural and accessory sural nerves of the cat. Fibers were classified into types on the basis of their receptor properties. Fibers of a particular type were found to have a characteristic range of conduction times. Fibers of the same type in different nerves were found to have similar skin-to-nucleus conduction times despite differences in conduction distance. These data enable one to predict the temporal characteristics of the input to the nucleus evoked by an abrupt stimulus at the skin. Conduction times from the sciatic nerve to the gracile nucleus were also determined. Comparison was made between the temporal dispersion of the input evoked by electrical stimulation of the sciatic nerve and the first spike latencies of post-synaptic cells in the nucleus excited by the same stimulus. The range of arrival times of the input closely matched the distribution of postsynaptic first spike latencies.