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consists of a motor neuron and all the muscle fiber it supplies. when a motor neuron fires(transmits action potential) all the muscle fibers it innervates contract
first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, muscle tension is beginning to increase but no response is seen on the myogram
Period of contraction
when cross-bridges are active, from the onset to the peak of tension development,
graded muscle response
muscle contraction graded in 2 ways
1) by changing the frequency of stimulation
2) changing the strength of stimulation
Temporal or wave summation
occurs because the second contraction occur before the muscle has completely relaxed.
unfused or incomplete tetanus
stimulus strength is held constant and the muscle is stimulated at an increasingly faster rate. sustained but quivering contraction
fused or complete tetanus
all evidence of muscle relaxation disappears and contractions fuse in a smooth sustained contraction plateau
muscle shortens and does work (picking up a book or kicking a ball)
muscle generates force as it lengthen. important for coordination and poseful movements. (walking up a heal...calf muscle)
tension may build up but muscle neither shortens or lengthens. load that is trying to be lifted is too heavy (trying to lift a piano)
requires oxygen and involves a sequence of chemical reactions in which the bonds of fuel molecules are broken and the energy released is used to make ATP
extra amount of oxygen for totally aerobic muscle activity and the amount actually used
force of muscle contraction affected by
1) number of muscle fibers stimulated
2) relative size of fibers
3) frequency of stimulation
4) degree of muscle stretch
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