Use myograph F-2000. Balance and calibrate the myograph so that 4 cm of pen deflection = 100 grams.
Set up Frog sciatic Neuromuscular Preparation as described in Exercise #2 (lab manual pg. 15 - 20) and Ex. 4 (pg. 37 - 39). Be very carful not to stretch or damage the sciatic nerve when isolating and positioning the sleeve electrode on it. Test to find threshold and maximal stimuli voltages before proceeding to part A. When you change to another leg during the experiment you must find the new threshold and maximal voltage specific for that setup. If your setup lasts until Part C you should switch legs before going on to part D. If you cannot proceed because the sciatic or gastrocnemius is fatigued before you get to part C, you will eventually need another frog. Therefore, you should take care and only stimulate the nerve when necessary.
Part A: Motor Unit Summation
Transducer: F-2000
Paper Speed: .25 cm/sec
Timer: 10 sec
Stimulus: Electrical
Intensity: Variable
Frequency: Single
Duration: 2 msec
Methods: stimulate, wait 10 seconds (and adjust voltage), stimulate again, repeat until 3 contractions of the same force are recorded (indicating that all motor units are recruited).See pg. 41 in your lab manual.
Labels on Record: Label time and event marker with voltages applied, label force (g) of all contractions, note threshold response and maximum response.
Generation of Tetany
Transducer: F-2000
Paper Speed: .5 cm/sec
Timer: 1 sec
Stimulus: Electrical
Intensity: (maximal voltage from part A)
Frequency: Variable (2,4,8,12,16,20,30 and 40 per second)
Duration: 2 msec
Methods: Stimulate for 2 seconds (hold the button on continuous for two clicks of the 1 sec timer), rest for 10 sec (and increase frequency), stimulate for 2 seconds again at the new frequency, repeat. See page 41 in your lab manual.
Label record: label time and event marker with frequency of stimulus applied, maximum force of each group of contractions, incomplete and complete tetany.
Part B: Normal Form Curve
Transducer: F-2000
Paper Speed: 10 cm/sec
Timer: OFF
Stimulus: Electrical
Intensity: (maximal voltage from part A)
Frequency: Single
Duration: 2 msec
Methods: Try a single stimulus at a slower paper speed to test pen deflection. If you don’t get 2-3 cm of pen deflection increase the tension on myograph. Then proceed with the record. See page 47 of your lab manual.
Label: Mark off, label and note the length of each of the 3 periods in seconds (Latency, Contraction, and Relaxation). Measure the force of the contraction (g).
Part C: Effect of Temperature on periods of the Normal Form Curve
Transducer: F-2000
Paper Speed: 10 cm/sec
Timer: OFF
Stimulus: Electrical
Intensity: (maximal voltage from part A)
Frequency: Single
Duration: 2 msec
Methods: Record a normal form curve at room temperature first (T1). Then, with the record off, apply ice to the gastrocnemius for two minutes, being carful not to pull the muscle loose from the myograph hook. Then record T5 to T2, as the muscle slowly warms. You may need to wait 30 sec. between each contraction to allow warming. See page 47 in your lab manual.
Labels: Mark off, label and note the length of each of the 3 periods in seconds (Latency, Contraction, and Relaxation) and measure the force of the contraction (g) for each of the 5 normal form curves. Label the curves from warmest to coldest as T1 through T5.
Graphs: For the Time vs. Temperature graph Temperature should be labeled as T1 through T5 on the X-axis and time on the Y-axis in seconds. You should have 3 lines on this graph, each showing the change in lengths of the 3 periods (Latency, Contraction, and Relaxation) over different temperatures.
Part D: Effect of Fatigue on periods of the Normal Form Curve
ReturnTransducer: F-2000
Paper Speed: 10 cm/sec
Timer: OFF
Stimulus: Electrical
Intensity: (maximal voltage from part A)
Frequency: Single
Duration: 2 msec
Methods: Record a normal form curve without fatigue (F1). Then, with the record off, fatigue the gastrocnemius by stimulating at a frequency of 4 per second for 10 to 15 seconds. Then record F2 to F5. Be sure and record the normal form curve immediately after you stop stimulating to fatigue. If you wait after you fatigue you may not see any change in the shape of the normal form curve. See page 47 in your lab manual.
Labels: Mark off, label and note the length of each of the 3 periods in seconds (Latency, Contraction, and Relaxation) and measure the force of the contraction (g) for each of the 5 normal form curves. Label the curves as F1 through F5.
Data Table: List the Force (g), Length of Latency (sec), Length of Contraction (sec), and Length of Relaxation for each of the 5 normal form curves in table format for comparison.