Spinal motoneurons (MNs) relay neural commands from the brain to the muscles to produce functional movement. However, MNs are more than passive conduits of neural commands; they also shape motor output through alterations in their intrinsic excitability. These alterations allow MNs to modify (e.g., amplify and/or prolong) motor output even in the absence of descending motor commands. How MNs respond to this modulation, under various conditions, is not fully understood. In the scope of this dissertation, we leverage high-density electromyography and motor unit decomposition algorithms to investigate how human MNs behave in (Aim 1) different muscles under similar task demands; (Aim 2) the same muscle under different task demands; and (Aim 3) in response to exogenous neuromodulation. First, in Aim 1 we demonstrate that MN excitability varies across motor pools and, thus, may be functionally tuned to the task and its muscle-specific demands. The results indicate that the MN discharge rates were significantly higher in the first dorsal interosseous, a small hand muscle used for fine motor control. Conversely, higher MN excitability was observed within the tibialis anterior, a lower leg muscle involved in balance and locomotion. Next, in Aim 2 we show that a muscle (i.e., the biceps brachii) with multiple biomechanical functions (e.g., supination and flexion) receives differential synaptic input to perform each action while the MN discharge characteristics remain the same. Finally, in Aim 3 we demonstrate that a single cup of coffee can alter fundamental motor control mechanisms by increasing discharge rate, inter-pulse variability, and excitability through caffeine-induced neuromodulation. Collectively, findings from this dissertation demonstrate the human motor system’s tremendous ability to adapt to internal and external states. / Public Health
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/8547 |
| Date | January 2023 |
| Creators | Taylor, Christopher, 0000-0003-0609-6624 |
| Contributors | Thompson, Christopher K., Wright, Geoffrey W., Negro, Francesco, McPherson, Laura, Hiremath, Shivayogi |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 143 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/8511, Theses and Dissertations |
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