Procedure F Sustained Contraction

1. To record a sustained muscle follow these steps:

a. Set the stimulator for continuous stimulation.

b. Set the voltage for maximal muscle contraction as determined in Procedure D.

c. Set the frequency of stimulation at a minimum.

d. Set the paper speed at about 0.05 cm/sec.

e. With the paper moving, administer electrical stimulation and slowly increase the frequency of stimulation until the muscle sustains a contraction (tetanic contraction or tetanus). f. Continue to stimulate the muscle at the frequency that produces sustained contractions until the muscle fatigues and relaxes.

2. Every 15 seconds for the next several minutes, stimulate the muscle to see how long it takes to recover from the fatigue.

3. Complete Part D of the laboratory report.

OPTIONAL ACTIVITY

T o demonstrate the staircase effect (treppe), obtain a fresh frog gastrocnemius muscle and attach it to the recording system as before. Set the paper control for slow speed, and set the stimulator voltage to produce a maximal muscle contraction. Stimulate the muscle once each second for several seconds. How do you explain the differences in the lengths of successive muscle contractions?_

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