Balance and calibrate the F-2000 Myograph so that 4 cm = 100 g. Set up the frog sciatic neuromuscular preparation and attach the rocker switch to your stimulator and sleeve and pin electrodes. Place the pin electrodes in the gastrocnemius and attach the sleeve electrode to the sciatic nerve. See page 52 for a picture of this setup. Be gentle with the sciatic nerve. If it is damaged the experiment will not work.
Part A: Site of First Fatigue
Transducer: F-2000
Paper Speed: .5 cm/sec
Timer: 1 sec
Stimulus: Electrical
Intensity: Optimal (use the voltage that gives you equal forces for stimuli via nerve and via muscle)
Frequency: 4 per second (disregard lab manual)
Duration: 2 msec
Special Equipment: Rocker Switch
Methods: Experiment with the voltage and tension to obtain contractions via nerve stimulation and direct muscle stimulation that are the same height. Show these controls on your record. Give a single stimulus via nerve, wait 10 sec., give a single via muscle, wait 10 sec., repeat via nerve 3 times (with 10 sec between) then flip the stimulator to continuous via nerve, when the force of contractions begins to decrease (measurably) flip the rocker switch (quickly) to muscle.
Label: Force of contraction for each of the controls (single stimuli at the beginning), force of contraction for the first contraction and last contraction while stimulating continuous via the nerve, and force of the first contraction when stimulation continuously via the muscle. Block off and label areas stimulated continually via nerve and muscle, also label single stimuli (as stimulus via nerve or stimulus via muscle).
Part B: Mechanical Stimulus
Transducer: F-2000
Paper Speed: .5 cm/sec
Timer: 10 sec
Stimulus: Mechanical
Methods: Pinch at 2 different sites, but make sure you pinch proximal to the sleeve or you will not be able to use this leg for the next experiment. Turn the record on and pinch the sciatic nerve with forceps or hemostats, hard enough to produce a measurable contraction. Move proximal and try again. This time you should get a smaller contraction. Why?
Label: Force of contractions, mark event bar where pinches occurred.
Part C: Effect of Lidocaine/Ether
Transducer: F-2000
Paper Speed: .1 cm/sec
Timer: 10 sec
Stimulus: Electrical
Intensity: Optimal
Frequency: Single
Duration: 2 msec
Stimulus: Chemical
Drug applied: Lidocaine (2%)
Dosage: 2 drops
Special Equipment: Rocker Switch
Methods: Experiment with the voltage and tension to obtain contractions via nerve stimulation and direct muscle stimulation that are the same height. To show these controls on your record, give a single stimulus via nerve, wait 10 sec., give a single via muscle, wait 10 sec., repeat via nerve 3 times (with 10 sec between). Apply 2 drops of Lidocaine (2% solution) to the sleeve. Make sure the sleeve is filled, but don’t get any on the gastrocnemius. Don’t forget to hit the event button to mark when the drug was applied. Stimulate at 20 second intervals via the nerve until the force shows a decrease of 40%, then stimulate the muscle directly 3 times at 20 sec intervals.
Label: Force of contraction for all controls, and every contraction following. Label stimuli as via nerve or via muscle. Label event mark where drug was applied.
Part D: Effect of d-tubocurare/succinylcholine chloride
ReturnTransducer: F-2000
Paper Speed: .1 cm/sec
Timer: 10 sec
Stimulus: Electrical
Intensity: Optimal
Frequency: Single
Duration: 2 msec
Stimulus: Chemical
Drug applied: D-tubocurare (1 mg/ml)
Dosage: 2 drops on nerve, .8ml injected into muscle
Special Equipment: Rocker Switch
Methods: On a new leg, set up the preparation and experiment with the voltage and tension to obtain contractions via nerve stimulation and direct muscle stimulation that are the same height. To show these controls on your record, give a single stimulus via nerve, wait 10 sec., give a single via muscle, wait 10 sec., repeat via nerve 3 times (with 10 sec between). Apply 2 drops of DTC to the sleeve around the sciatic nerve. Continue to stimulate once every 20 seconds via the nerve for 4 stimuli. Now, inject DTC in small pockets throughout the gastrocnemius muscle. Stimulate via the nerve until the force decreases by 75%, switch to stimuli directly to muscle and stimulate once every 20 sec for 1 minute. (see page 74).
Label: Force of all controls, force of first and last contraction after DTC applied to nerve, first and last contraction after DTC is injected into the muscle and first and last contraction after the rocker switch is flipped to muscle, note if stimuli are via nerve or muscle.