Lab 3: Excitability & Response
of Skeletal Muscle
Objectives
รศ ดร นพ ชยเลศ
รศ.ดร.นพ.
ชัยเลิศ พิพชตพรชย
ชิตพรชัย
ภาควิชาสรีรวิทยา
คณะแพทยศาสตรศิริราชพยาบาล
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 Æ Summation of m. contraction
4. Fatigue mechanism
Muscle Physiology
Materials
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Chailerd Pichitpornchai
PowerLab
o e ab Set
Selecting switch box
3
Muscle Physiology
Chailerd Pichitpornchai
Experimental Design
1. Threshold & Maximal stimuli of Nerve & Muscle
1. Threshold & Maximal stimuli of Nerve & Muscle
2. Length-Tension Relationship
3. Effect of Double Stimulation
4.4 Effect of Repetitive Stimulation
5. Muscular Fatigue
g
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Muscle Physiology
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Force transducer
Tissue: Gastrocnemius-sciatic preparation
Electronics: PowerLab, Dual Bio Amp., Quad Bridge
Amp Force Transducer
Amp.,
Muscle tension adjuster, Selecting switch box
Electrodes :- Sleeve, Needles
S i l iinstrument
Surgical
t
t
Frog board, Femur clamp
Muscle Physiology
Chailerd Pichitpornchai
Chailerd Pichitpornchai
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4
Stimulate
„ Sciatic Nerve
„ Gastrocnemius
G
i Muscle
M l
Record
„ Muscle Contraction Æ Channel 1
„ Compound muscle action potential Æ Channel 2
Æ Electromyograph (EMG)
Muscle Physiology
Chailerd Pichitpornchai
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Conceptual Design (1): Stimulate Nerve
1. Muscle contraction
Duration
Force transducer
Delay
+
Bridge Amp
Channel 1
Rate of rise
(slope)
Channel 2
–
Bio Amp
Channel 3
Stimulator
Muscle Physiology
Marker
2. EMG
Chailerd Pichitpornchai
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Channel settings
Muscle Physiology
Chailerd Pichitpornchai
Chailerd Pichitpornchai
Chailerd Pichitpornchai
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Channel 1 – Bridge Amp Æ Muscle Contraction
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Channel 2 – Bio Amp Æ EMG or CAP
Muscle Physiology
Muscle Physiology
Muscle Physiology
Chailerd Pichitpornchai
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Stimulator setting
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Calibration & Unit Conversion
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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...
Conversion
„ Select 2 p
point calibration
0.5 s
Muscle Physiology
Chailerd Pichitpornchai
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Calibration & Unit Conversion
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1.1 Stimulate Sciatic Nerve
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Muscle Physiology
Chailerd Pichitpornchai
Chailerd Pichitpornchai
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Stimulate via SLEEVE electrodes
„ Voltage 200 mV + increment 50 mV
R d
Record
„ Mechanical response Æ Muscle contraction
„ Electrical response Æ EMG or Compound M. AP
Observe
„ Threshold, submaximal, maximal, supramaximal stimuli
Muscle Physiology
Chailerd Pichitpornchai
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Muscle Physiology
Chailerd Pichitpornchai
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Conceptual Design (2): Stimulate Muscle
1. Muscle contraction
Force transducer
Channel 1
+
–
Bridge Amp
Channel 2
Channel 3
Bio Amp
Marker
Stimulator
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Chailerd Pichitpornchai
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1.2 Stimulate Gastrocnemius Muscle
Activity 1
Stimulate muscle via NEEDLE electrodes
„ Voltage 200 mV + increment 100 mV Æ threshold
„ + increment
i
t 500 mVV Æ maximal
i l stimulus
ti l
Record mechanical response Æ Muscle contraction
Channel 2 Æ Turn Input Off
Selecting
l i switch
i h bbox Æ Needle
dl Stimulator
i l / Off Recording
di
Observe Æ Threshold, submaximal, maximal, supramaximal stimuli
1. Compare the threshold of nerve stimulation & muscle
stimulation
2. Compare the maximal stimulus of nerve stimulation &
muscle stimulation
3. Why?
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2. Length-Tension Relationship
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Muscle tension adjuster
Stimulate N. Æ Single pulse, Maximal Stimulus
Record Æ Muscle Contraction & EMG
Ch Æ
Change
„ Muscle tension adjuster anti-clockwise
1 Æ 2 Æ 3 Æ 4 Æ 5 Æ ...
„ Muscle
M l ttension
i adjuster
dj t clockwise
l k i
... Æ 5 Æ 4 Æ 3 Æ 2 Æ 1
Muscle Physiology
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Muscle Physiology
Chailerd Pichitpornchai
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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
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3. Effect of Double Stimulation
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Stimulator setting for Double stimuli
Adjust Æ Muscle tension adjuster to get the highest
response
Stimulate N. Æ 2 pulses, Maximal stimulus
Change Interval: 500 ms, decrement 50 ms at a time
until a single complete summation of muscle contraction is
observed
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Muscle Physiology
Activity 3
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Stimulator setting for Repetitive stimuli (10 Hz)
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4. Effect of Repetitive Stimulation
1. Observe Summation of contraction
2. Observe EMG
Muscle Physiology
Chailerd Pichitpornchai
Chailerd Pichitpornchai
Adjust Æ Muscle tension adjuster to get the highest response
Stimulate N. with maximal stimulus
Stimulate 3s + Rest 20s
Change Frequency: 10 Æ 20 Æ 30 Æ 40 Hz
Number of ppulses: 30 Æ 60 Æ 90 Æ 120 ppulses
Muscle Physiology
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Stimulator setting for Repetitive stimuli (20 Hz)
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Stimulator setting for Repetitive stimuli (30 Hz)
Muscle Physiology
Chailerd Pichitpornchai
Stimulator setting for Repetitive stimuli (40 Hz)
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Activity 4
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Stimulator setting for fatigue : stimulating N.
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5. Muscular Fatigue
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
Chailerd Pichitpornchai
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Adjust Æ Muscle tension adjuster
Stimulate N. Æ Maximal stimulus
„ Frequency 40 Hz and wait until the amplitude is 1/3 left
„ Click Off in the Stimulator
Channel 2 Æ Turn Input Off
Selecting switch box Æ Needle Stimulator / Off Recording
Stimulate Muscle directly with 5 V
„ Click On in the Stimulator
Stim lator
Muscle Physiology
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Stimulator setting for fatigue: stimulating M.
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Activity 5
More Questions…
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
Neuromuscular fatigue”
fatigue
and “Muscle fatigue” ?
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
Muscle Physiology
Chailerd Pichitpornchai
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Chailerd Pichitpornchai
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