Submitted by: Submitted by Iamstep96
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Category: English Composition
Date Submitted: 09/11/2015 08:19 PM
he bones of the skeleton provide support for the body and articulate at joints, which act as pivot
points. The associated skeletal (or striated) muscles are connected to the bones either directly, or by
strong bundles of collagen called tendons. Two or more muscles usually work antagonistically so
that a contraction of one stretches the other. Skeletal muscle is composed of large multinucleate
cells called fibres. An action potential in a motor axon produces an action potential in the muscle
fibres it innervates. The effect of the action potential is to increase the intracellular level of calcium
for a short time, providing a signal to the contractile molecular machinery inside the fibre, and
resulting in a brief contraction (a ‘twitch’).
A whole muscle may be innervated by hundreds of motor axons. One way the nervous system
can control the amount of movement is to control the number of motor axons firing, thus controlling
the number of twitching muscle fibres. This process is called recruitment.
A second way the nervous system controls the amount of muscle contraction is to vary the
frequency of action potentials in the motor axons. At frequencies less than 5 Hz, there is enough
time for the intracellular calcium to recover to normal between action potentials: the contraction
consists of separate twitches. At frequencies in the range 5 to 15 Hz, the calcium concentration in
one twitch has only partly recovered when the next action potential arrives. The muscle fibre
produces pulsatile tension (a ‘summation response’) whose peak is greater than that of a single
twitch, and which does not decay completely to zero between pulses. At even higher frequencies,
the pulsatile component becomes hard to discern, and the fibre produces a smooth contraction
(‘tetanus’) many times stronger than that in a single twitch.
In part A, you observe muscular responses without recording them. In part (B) and (C), you use
the finger pulse transducer to measure...