Question Muscle Q 1. Did you get a measurable twitch with a stimulus of 0 mA? What does this tell you about the number of muscle fibers contracting at this stimulus current? [1]

2. What was the smallest current required to produce a contraction (the threshold current)? What proportion of the fibers in the muscle do you think were contracting to produce this small response? [1]

3. What was the smallest current required to produce the maximum (largest) contraction? What proportion of the fibers in the muscle do you think were contracting to produce this maximal response? [1]

4. What do you conclude happened to the number of fibers contracting as the current was raised from threshold to that required to produce a maximal contraction? [1] 5. Why does varying the stimulus strength affect the twitch force? [1] Exercises 3 & 4: Summation and tetanus

6. The stimulus interval has a profound effect on the contraction force of the muscle. In your own words explain what happened when the muscle was stimulated in rapid succession. What was the minimum time required for the subject's muscle twitches to add together (summation)? [2]7. You use a short period electrical stimuli to observe muscle fibers contracting continuously (tetanus). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called 'spastic paralysis'! Explain in your own words why these agents would be a bad thing for you and your muscles. [3]