Lab 3: Excitability & Response of Skeletal Muscle รศ.ดร.นพ. ช ยเล ศ ชยเลศ พ ช ตพรช ย พชตพรชย ภาคว ชาสร รว ทยา คณะแพทยศาสตร ศ ร ราชพยาบาล Objectives 1. Threshold, submaximal, maximal, supramaximal stimulus of 1.1 Nerve & 1.2 Muscle 2. Length-Tension Relationship - Physiological length or Resting length 3. Repetitive stimuli Summation of m. contraction 4. Fatigue mechanism Muscle Physiology Chailerd Pichitpornchai 2 Materials Tissue: Gastrocnemius-sciatic preparation Electronics: PowerLab, Dual Bio Amp., Quad Bridge Amp., Force Transducer Muscle tension adjuster, Selecting switch box Electrodes :- Sleeve, Needles Surgical instrument t Frog board, Femur clamp Force transducer Selecting switch box PowerLab Set Muscle Physiology Chailerd Pichitpornchai 3 Muscle Physiology Chailerd Pichitpornchai 4 Experimental Design 1. Threshold & Maximal stimuli of Nerve & Muscle 2. Length-Tension Relationship 3. Effect of Double Stimulation 4. Effect of Repetitive Stimulation 5. Muscular Fatigue 1. Threshold & Maximal stimuli of Nerve & Muscle Stimulate Sciatic Nerve Gastrocnemius Muscle Record Muscle Contraction Channel 1 Compound muscle action potential Channel 2 Electromyograph (EMG) Muscle Physiology Chailerd Pichitpornchai 5 Muscle Physiology Chailerd Pichitpornchai 6
Conceptual Design (1): Stimulate Nerve Duration Delay Force transducer 1. Muscle contraction Rate of rise (slope) Channel 1 Bridge Amp Channel 2 + Bio Amp Channel 3 Marker Stimulator 2. EMG Muscle Physiology Chailerd Pichitpornchai 7 Muscle Physiology Chailerd Pichitpornchai 8 Channel settings Channel 1 Bridge Amp Muscle Contraction Muscle Physiology Chailerd Pichitpornchai 9 Muscle Physiology Chailerd Pichitpornchai 10 Channel 2 Bio Amp EMG or CAP Stimulator setting Muscle Physiology Chailerd Pichitpornchai 11 Muscle Physiology Chailerd Pichitpornchai 12
Calibration & Unit Conversion 0.5 s Put 50 g weight on the 3 blades of force transducer Click Start to record the 50 g force in Channel 1 From the Channel function pop-up menu Select Unit Conversion... Select 2 point calibration Muscle Physiology Chailerd Pichitpornchai 13 Muscle Physiology Chailerd Pichitpornchai 14 Calibration & Unit Conversion 1.1 Stimulate Sciatic Nerve Stimulate via SLEEVE electrodes Voltage 200 mv + increment 50 mv Record Mechanical response Muscle contraction Electrical response EMG or Compound M. AP Observe Threshold, submaximal, maximal, supramaximal stimuli Muscle Physiology Chailerd Pichitpornchai 15 Muscle Physiology Chailerd Pichitpornchai 16 Conceptual Design (2): Stimulate Muscle Force transducer 1. Muscle contraction Channel 1 Bridge Amp + Channel 2 Channel 3 Marker Bio Amp Stimulator Muscle Physiology Chailerd Pichitpornchai 17 Muscle Physiology Chailerd Pichitpornchai 18
1.2 Stimulate Gastrocnemius Muscle Stimulate muscle via NEEDLE electrodes Voltage 200 mv + increment 100 mv threshold + increment 500 mv maximal stimulus Record mechanical response Muscle contraction Channel 2 Turn Input Off Selecting switch box Needle Stimulator / Off Recording Observe Threshold, submaximal, maximal, supramaximal stimuli Activity 1 1. Compare the threshold of nerve stimulation & muscle stimulation 2. Compare the maximal stimulus of nerve stimulation & muscle stimulation 3. Why? Muscle Physiology Chailerd Pichitpornchai 19 Muscle Physiology Chailerd Pichitpornchai 20 2. Length-Tension Relationship Muscle tension adjuster Stimulate N. Single pulse, Maximal Stimulus Record Muscle Contraction & EMG Change Muscle tension adjuster anti-clockwise 1 2 3 4 5... Muscle tension adjuster clockwise... 5 4 3 2 1 Muscle Physiology Chailerd Pichitpornchai 21 Muscle Physiology Chailerd Pichitpornchai 22 Activity 2 1. Observe changes of amplitude of m. contraction at different initial length 2. What is resting length or physiological length? 3. Explain why does the amplitude of m. contraction change in relation to muscle initial length Muscle Physiology Chailerd Pichitpornchai 23 Muscle Physiology Chailerd Pichitpornchai 24
3. Effect of Double Stimulation Stimulator setting for Double stimuli Adjust Muscle tension adjuster to get the highest response Stimulate N. 2 pulses, Maximal stimulus Change Interval: 500 ms, decrement 50 ms at a time until a single complete summation of muscle contraction is observed Muscle Physiology Chailerd Pichitpornchai 25 Muscle Physiology Chailerd Pichitpornchai 26 Activity 3 1. Observe Summation of contraction 2. Observe EMG 4. Effect of Repetitive Stimulation Adjust Muscle tension adjuster to get the highest response Stimulate N. with maximal stimulus Stimulate 3s + Rest 20s Change Frequency: 10 20 30 40 Hz Number of pulses: 30 60 90 120 pulses Muscle Physiology Chailerd Pichitpornchai 27 Muscle Physiology Chailerd Pichitpornchai 28 Stimulator setting for Repetitive stimuli (10 Hz) Stimulator setting for Repetitive stimuli (20 Hz) Muscle Physiology Chailerd Pichitpornchai 29 Muscle Physiology Chailerd Pichitpornchai 30
Stimulator setting for Repetitive stimuli (30 Hz) Stimulator setting for Repetitive stimuli (40 Hz) Muscle Physiology Chailerd Pichitpornchai 31 Muscle Physiology Chailerd Pichitpornchai 32 Activity 4 1. Observe Incomplete & Complete Tetanus 2. Compare Amplitude of m. contraction between Complete & Incomplete Tetanus 3. EMG during Complete & Incomplete Tetanus Muscle Physiology Chailerd Pichitpornchai 33 5. Muscular Fatigue Adjust Muscle tension adjuster Stimulate N. Maximal stimulus Frequency 40 Hz and wait until the amplitude is 1/3 left Click Off in the Stimulator Channel 2 Turn Input Off Selecting switch box Needle Stimulator / Off Recording Stimulate Muscle directly with 5 V Click On in the Stimulator Muscle Physiology Chailerd Pichitpornchai 34 Stimulator setting for fatigue : stimulating N. Stimulator setting for fatigue: stimulating M. Muscle Physiology Chailerd Pichitpornchai 35 Muscle Physiology Chailerd Pichitpornchai 36
Activity 5 1. Observe amplitude of muscle contraction 2. What's happened to the Action Potential of the muscle during fatigue? 3. What is the difference between Neuromuscular fatigue and Muscle fatigue? More Questions 1. Why doesn't the amplitude of muscle contraction increase when we stimulate with supramaximal stimulus? 2. Why does the tetanic contraction have a higher amplitude than single muscle twitch? Muscle Physiology Chailerd Pichitpornchai 37 Muscle Physiology Chailerd Pichitpornchai 38