Year: 1995
Type: dissertation
Abstract: The present thesis addressed two broad questions about the physiology of human alpha motoneurons: 1) how does the central nervous system recruit the neurons in a motoneuron pool when performing various tasks; and 2) can the biophysical properties of human motoneurons be indirectly assessed and compared with those of the cat?For the recruitment studies two sets of experiments were performed.The first set examined the hypothesis that the motoneurons innervating the flexor carpi ulnaris (FCU) muscle are fractionated into subpopulations, and that each of these subpopulations is recruited during a distinct task.The results of the present study did not support this hypothesis, but instead suggested that motoneurons in the motoneuron pool are recruited in the same order during the tasks presented in this study.The second set of recruitment experiments examined the order of recruitment of first dorsal interosseus (1DI) motoneurons during natural motor behaviour.The results of these experiments demonstrated that recruitment proceeds in the same fashion during a behavioral task as that during the more restrictive condition of an isometric contraction.The present investigation of the biophysical properties of human motoneurons was accomplished by measuring motoneuron excitability during rhythmic firing.The excitability of motoneurons was measured by the probability of their response to inputs from two sources: 1) muscle stretch receptors; and 2) neurons in the motor cortex.The results of these experiments demonstrated that the level of ongoing activity of the motoneuron, as determined by its firing rate, is a significant factor affecting its ability to respond to an input.In an effort to explain these results, a computer simulation of motoneuron stimulus/response behaviour was undertaken based upon known properties of the cat motoneuron.The result of this modeling suggests that the basic biophysical properties of the cat motoneuron are sufficient to account for the observed responses of human motoneurons to synaptic inputs. Table of Contents...
Source: Summit (Simon Fraser University)
Author: Kelvin E. Jones
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2276488294