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Muscle Physiology

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Damarcus D Hunt -May 13, 2011


The contraction of muscle fibers is a process requiring several molecules including, ATPase, magnesium, and potassium. Also muscle contraction is controlled by the amount of action potential the muscle receives. Frist we observe the changes in length and width after adding ATP, magnesium and calcium to a rabbit muscle. Next experiment was focused on measuring the strength of contractions in the arm and how much force is need to maintain a constant force before the muscle fatigues.


Functional Glycerinated Fibers:

A muscle fiber was taken from a rabbit and placed on a slide. Treated with a series of solutions ATP, KCl and, MgCl. Muscle contractions were observe under low magnification and the width and length were recorded. Three trials were run by adding ATP, salt and then ATP + salt.

Forced Contractions:

Using of an EMG sensor and logger pro to measure the amount of motor unit activity in bicep muscles of a group member. The subject in the first test held a hand dynamometer for 20 seconds at four varying levels of pressure (zero, light, medium and large). The potentials peaks were measured and recorded. The second test dealt with fatigue. The subject held the hand dynamometer for 60 seconds with a maximum amount of force. Peaks were recorded at the maximal point and when the subject started to fatigue. Measuring latency was the last test. In this test the subject applied a maximum amount of force on the hand dynamometer after 10 seconds had elapsed. Time measurements were taken when the potentials increased and when the force increased.


By adding a mixture of ATP and salt to a muscle forces a contraction. The fresh muscle started at 1.1 cm and after adding two drops of the ATP and salt solution it decreased in size to 0.8 cm(Table 1) Table 2 shows that by adding only salt has no change the muscle length. When adding only ATP there is a change in the length of the muscle fiber. Adding two drops of ATP decreased the length of the muscle from 1.4 cm to 1.35 cm. When a higher force was added it did not increase the average potential. The force exerted on the large load was strong enough to cause the readings for potential to become noise. The fatigue test measured a decrease in force, over time, and a slight increase in potential. During the fatigue test the muscle was working extremely hard to keep a constant force exerted which at about 17 seconds became recorded as noise. Table 3 shows the latency period at 0.196 seconds which is the amount of time for the brain to process the motor unit activity.


Latency is the time period between



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