1. Read each question carefully and answer completely. a. (2 points) Which type
ID: 34250 • 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 gradual activation of more motor units, during the graded contraction of the muscle tissue is called as motor unit recruitment. Motor unit recruitment is critical for the increased force of contraction of a muscle tissue. A muscle tissue contains several motor units; the force of muscle contraction depends upon the number of motor units excited by the stimulus, which again depend upon the intensity of the stimulus. If more number of motor units are excited gradually, a stronger contraction of the muscle results. If a few motor units are excited at a rapid rate, a smooth and weak muscle contraction results.
During the generation of weakest forces, slow motor units are recruited, and during the generation of strong contractions, fast - or non-fatiguable motor units are recruited.The desire effect can only be acheived with slow motor units, and they respond to the threshold generated by weak stimulus than the fast muscles. Fast fibres also generate more force thn the required one.
b). During muscle contraction, each muscle fibre passes through three phases namely, latent, contraction and relaxation phase. Latent period is the time required for the generation of action potential, latent period is immediately followed by the contraction phase (shortening of muscle fibres). Contraction period is followed by the relaxation phase during which the fibres lengthen again and relax to reach the normal state.
During rapid stimulation, the relaxation phase is not generally completed by muscle fibres, instead tehy recieve another stimulus, after pertial repolaraziation and results in tetanus (fused or unfused). Rapid stimulation of a muscle fibres (applied during contraction period) causes summation of the contractions and a single curve is obtained, which indicates a stronger, non-twirchy contraction of the muscle.
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