Since my first Anatomy and Physiology class in high school, I have found the subject of health and human performance very interesting. When I came to UF, I took an Anatomy class and my teaching assistant briefly explained her research on the first day. I was fascinated by the idea of connecting what we know about healthy individuals movements to diseased populations specifically those with Transient Ischemic Attack, Parkinson’s Disease, Essential Tremor and Cerebral Spinal issues. I got involved in the Neuromuscular Physiology Lab because the research is interesting and influential to the scientific community as well as a wide variety of individuals.
Motor Unit Characteristics of Fast, Targeted Contractions
A motor unit is single motor neuron and all the muscle fibers it innervates. The motor unit is important because it is the last common pathway of the nervous system to the muscle. Motor units relay messages to the muscles to tell the muscle to begin to contract. Most of what we know about the characteristics of motor units are based off of slow, steady contractions. However, not much is known about the characteristics of fast, ballistic contractions. The purpose of our research is to determine the general properties of motor units by looking at fast ballistic contractions, specifically by manipulating force and time. In one condition we will control force and increase time and in the other condition we will increase force and control time. This will enable us to see how the properties of the motor units are changing with changes in force and time. We will carry out this experiment by having participants perform a fast-ballistic contraction with a specific target. We will manipulate the target based on the level of force or the amount of time to contract. We will collect force and surface EMG data and decompose the EMG data into individual motor units. Form there we will analyze motor units as a whole, to understand how a population of motor units are being controlled. Based on the findings of this project, we hope to expand these findings to patients with essential tremor, Alzheimer’s Disease, Transient Ischemic Attack and cerebellar disorders.
We know that small motor units produce a small force, while larger motor units generate a large force. The brain determines the amount of force needed to perform a task and sends a synaptic current to the muscle, progressively stimulating the smaller to larger motor units. To increase the force in slow motor unit contractions, we can increase the number of motor units, the rate at which the motor units release action potentials, and motor unit synchronization.
A muscle twitch is the response of a muscle cell or motor unit to a single end plate potential. The varying speeds in motor unit contractions is due to the distance between successive twitches. The faster the contraction the faster the end plate potential, the slower the contraction the slower the end plate potential.
In the end, we hope to compare the general features of fast motor unit contractions to what we understand in slow motor unit contractions. We plan on studying fast motor unit contractions by collecting healthy young adult’s EMG (electromyograph) and force sensor data while they perform goal-directed tasks. The data collected will enable us to analyze the frequency of the twitch and the time in which the twitches occurred. This will help us to further our understanding in fast motor unit contractions’ general characteristics which may lead to further research using fast contractions.