Properties of single central Ia afferent fibres projecting to motoneurones.

Publisher Website
Google Scholar
Abstract
Electrical potentials in the cat lumbosacral spinal cord evoked by the action of single medial gastrocnemius Ia afferent fibers were recorded using impedance, bevelled micropipette electrodes and the spike triggered averaging technique. Axonal potentials from the Ia fibers recorded extracellularly appeared as brief triphasic predominantly negative potentials. Terminal potentials recorded in regions of Ia afferent termination appeared as brief diphasic positive-negative waves, often with additional wavelets. Focal synaptic potentials, recorded extracellularly in regions of the medial gastrocnemius Ia afferent termination, appeared as slow (about 10 ms duration) negative potentials following terminal potentials. Excitatory post-synaptic potentials, recorded intracellularly in Ia target cells of the medial gastrocnemius, appeared as slow (about 10 ms duration) positive potentials following terminal potentials. Analysis of the temporal progression of these potentials through the Spinal cord allowed calculations of the Ia conduction velocity in the dorsal funiculus stem axon (50-60 ms), in major collateral branches (8-19 ms) and in terminal branches (0.2-1.0 ms). The number of major collateral branches (9 or fewer) and their spacing along the spinal cord (1071 .mu.m mean value) were determined by analyzing the pattern of single fiber potential latency minima and maxima along the rostrocaudal extent of the triceps surae motoneuron column. The structural and functional properties of medial gastrocnemius Ia afferent fibers are discussed in relation to recent single fiber anatomical data and the present single fiber electrophysiological data.