Chapter 1 - Muscle Fibers, Motor Units, and Motoneurons Flashcards
What is Muscle Heterogeneity? (Explain in detail)
Muscle Heterogeneity plays a major role in the movement patterns in response to exercise. It’s the contraction of the motor units combined to produce voluntary and stimulation-evoked contractions.
What is the current theory on orderly motor unit recruitment?
The Henneman’s size principle is the recruitment of motorneurons according to size and action potential.
What are the two means the central nervous system can increase through the strength of muscle contractions?
By increasing both active number of motor units and firing rates.
When discussing motoneurons and excitability, what is meant by motoneron size and how is it determined?
Motorneuron size is related to recruitment order and measured in reduced preperations. Estimated size by: axon level, histologically, electrophysiologically.
What is the relationship between membrane resistivity and motoneuron size?
RIN - input resistance > measure resistance to current injected into a cell, determined by cell surface area (motorneuron size & range of cell rin). Smaller cells have high resistance, larger cell have lower resistances. (more current can flow out across the conductance channels)
What factors determine action potential generation?
The amount of current that is coming into the cell, resting membrane potential (RMP), and the depolarization amplitude required to reach the threshold for spike generation.
Define afterhyperpolarization and the impact it has on minimal firing rates.
Afterhyperpolarization is a prolonged phase that follows the action potential, the duration of this phase varies systematically among motorneurons of different types. Afterhyperpolarization is attributed to the activation of calcium-activated potassium conductance that gradually declines after the spike.
What effect does stimulation have on late adaptaion?
Late adaption is the process by which firing frequency is decrease with sustained constant intensity excitation.
What are motoneuron PICs?
PICs - persistent inward currents, last a relatively long time. PICs underlie bistability and can be generated by direct intracellular or synaptic excitation.
What impact do motoneron PICs have on motor unit ecitability?
PICs lasts for several seconds after excitation is terminated. PICs manifests as a sustained decrease in membrane potential if the cell is already firing, as an increase in firing rate can outlast previous stimulation for several seconds (warmup method).
