1. Read each question carefully and answer completely. a. (2 points) Which type
ID: 35571 • Letter: 1
Question
1. Read each question carefully and answer completely. a. (2 points) Which type of motor unit(s) (Slow, non-fatigueable or fast, fatigueable) is recruited during the generation of the weakest forces; the strongest forces? Explain. b. (2 points) Under normal conditions a single muscle cell, receiving a high frequency of action potentials from a single motor neuron will generate unfused tetani. How could a whole muscle provide smooth (non-twitchy) movements if unfused tetani were occurring in each of its muscle cells?
Explanation / Answer
a)
The fast, fatigueable is recruited during the generation of the strongest forces and Slow (oxidative) is recruited during the generation of the weakest forces.
b)
If a motor unit has been extremely induced by motor neuron, then it will lead to production of a tetanic contraction. A tetanic contraction takes place a motor unit is induced by several impulses with maximum frequency. Every stimulus causes a twitch.
The tension in the muscle will reduce between successive twitches, if stimuli are delivered slowly enough. The tension in the muscle will increase between successive twitches, if stimuli are delivered with high frequency resulting in tetanic contraction. When tetanized, the contracting tension in the muscle remains constant in a steady state.
This is the maximal possible contraction. A rather complex series of events occurs within the time course of a single twitch. The action potential is evoked upon application of the stimulus. That action potential, in turn, propagates down the length of the muscle fibers and triggers the excitation-contraction coupling process (release of Ca2+ from the sarcoplasmic reticulum, binding of Ca2+ to troponin, etc.).
Once crossbridge cycling ensues, the muscle fibers contract, generating tension. Tension peaks, but then decreases as the activity of Ca2+ pumps in the sarcoplasmic reticulum reuptake Ca2+from the cytosol, lowering the ability of actin and myosin to form crossbridges, and reducing tension generation as the fibers stretch back to their original length.
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