experiment 1 - zhejiang universitym-learning.zju.edu.cn/g2s/ewebeditor/uploadfile/...to measure a...
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EXPERIMENT 1Effects on muscle of nerve stimulation at
different intensities and frequencies
Ying-ying Chen, PhDDept. of Physiology, Zhejiang University School of Medicine
bchenyy@zju.edu.cn
EXPERIMENTAL PHYSIOLOGY
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IntroductionThe functional unit of skeletal muscle activity is the motor unit
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Interposed between the axon branches and the muscle fibers is a structure called the neuromuscular junction (motor end-plate)
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Graded contractions can be obtained by activation of fewer or more of these neuronsThe individual nerve fibers posses different thresholds
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The most convenient way of examining the properties of the motor unit is by use the nerve-muscle preparation
gastrocnemius
sciatic nerve
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ObjectivesTo make a sciatic nerve & gastrocnemius (SNG) preparationTo measure the effects of different stimulus intensities on the muscle responseTo measure a single twitch, incomplete tetanus and complete tetanus
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Experimental animal: Toad
Parotid glands
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Ringer’s solution is a solution of recently boiled distilled water containing NaCl 6.5g, KCl 0.14g, CaCl2 0.12g, NaHCO3 0.20g, NaH2PO4 0.01g per liter
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Equipment RequiredRM6240 biological signal collecting systemForce transducer
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Intact Nerve-Muscle PrepPith the toad, resulting in the toad not feeling painAs soon as the brain and spinal cord destroyed, the toad should become flaccid
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Peel the skin of one leg
Fix the toad on the frog board with the dorsal surface uppermost
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Identify the gastrocnemius muscleTie a knot around the Achilles tendon using suture threadCut the Achilles tendon as close to the bottom of the foot as possible
Gastrocnemius
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Locate the sciatic nerve in the thigh regionUse the glass hooks to separate the sciatic nervePass a piece of thread beneath the sciatic nerve
Biceps femoris
Semimembranosus
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gastrocnemius
sciatic nerve
electrode
thread
Hold knee in place by pushing down two T-pinsTie the free end of the thread to the hole on the end of the tongue of the force transducerPlace the stimulating electrode on the sciatic nerve
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Warning: Do not touch the nerve with any
object that is made of metal; this will render
the nerve useless
Warning: Avoid stretching or otherwise
damaging the nerve. Keep the tissue moist
with frog ringer’s solution
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Start the softwareSwitch the RM6240 Data Acquisition System
Click on the “RM6240USB2.0q(I)(English)” icon
on the Desktop
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Exercise 1: effect of stimulus intensity on twitch amplitudeSet record parameters
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The recording trace should be set to zero
loose
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Apply a light load to the muscle by raising the force transducer with the tension adjuster until the trace moves approximately 2 g above the baselineWarning: Make sure to lift the muscle vertically to an angle that is perpendicular to the rest of the toad leg
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Display the stimulation mark
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Change the stimulus amplitude to 0.2VDetermine the threshold voltage by increasing the stimulus voltage in 0.01V increments
Stop and save the recording trace
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Data analysis
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Maximal intensity
Threshold intensity
Tension of contraction (g)Intensity stimulus (V)
Measure the following values:
threshold stimulus maximal stimulus
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Relaxation
Contraction
Latent periodDuration (ms)
Record the following values in a single twitch induced by maximal stimulus :
latent period
contraction relaxation
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Exercise 2: effect of stimulus frequency on twitch amplitude
Set record parameters
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Click on the record button Select the “frequency ascending mode”
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Display the stimulation mark
Begin the recording
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Set the stimulus intensity to the lowest value that will give strong contraction in the exercise 1
Stop and save the recording trace
6
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Data analysis
Determine the following values:
complete tetanus
incomplete tetanus
Single twitch
Tension of contraction (g)Frequency of stimulus (Hz)
twitch incomplete tetanus
complete tetanus