Lab 8
Skeletal Muscle Physiology
PhysioEx Disc or in
Mastering A&P
Assignment - Skeletal Muscle Physiology simulation
Use directions in handout. This PhysioEx experiment is on discs in the lab,
in Canvas, and can be accessed on Mastering A&P. It is also available in the
library. It is the simulation called Skeletal Muscle Physiology. Information
about muscle physiology is in Chapter 10 of the text.
Hand in for a grade at the next class, stapled together IN THIS ORDER:
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Lab 8 Sheet with questions answered.
Summary and Questions Sheet
Printed data from Activity 3 Labeled Table 1. Multiple Motor Unit
Summation above the table. 10 points.
Hand-plotted graph from Activity 3. Label Figure 1 below the graph. 10
points
Activity 5 - two labeled computer-generated graphs (from 4. and 6.). Label
Figure 2 and Figure 3 below the graphs. 10 points.
Activity 6- two labeled computer generated data plots (one from 8. and one
from 12.). Label Figure 4 and Figure 5 below the graphs. 10 points
Name______________________
Lab Section ________________
Lab 8
Microscopic Anatomy and Organization of Skeletal Muscle and Muscle
Physiology
Skeleton Muscle Physiology: Computer Simulation
Activity Sheet
Objectives:
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Use a simulation of skeletal muscle experiments to investigate threshold
stimulus, maximal stimulus, multiple motor unit summation, wave
summation and tetanus and the graded contraction.
Develop and test hypotheses related to muscle contraction.
Practice graphing data from an experiment.
Practice interpreting a graph and drawing conclusions from data.
Please follow these directions - Getting Started
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This exercise uses the PhysioEx disc in the back of your lab manual or available
online through Mastering A&P. The simulation is called Skeletal Muscle
Physiology
Obtain a laptop computer, power cord, mouse and mouse pad from the cabinet
and assemble it as directed by the instructor.
Open the computer and turn it on. Wait until the Windows screen opens.
Follow the screen directions to start the computer.
Open PhysioEx and Choose Skeletal Muscle Physiology from the menu at the
top of the screen. Then choose Single Stimulus. Take a minute to identify the
oscilloscope display, muscle sample in holder, stimulator, voltage control, data
recording area, time display, and force display. The muscle length should
always remain at 75 mm.
Any time you are instructed to Print, make a copy for each person in your
group. The printer is in S545.
Things to Remember as you Begin
1. You have control over the strength of the stimulus (voltage) and the
frequency of the stimulus (stimuli per second).
2. Increasing the voltage increases the strength of the stimulus.
3. Increasing the frequency increases the rate at which the muscle is being
stimulated.
4. These experiments illustrate two types of summation discussed in class:
a. multiple motor unit summation or recruitment and wave summation
and
b. fused tetanus. Your class notes should help you with the simulation.
Practicing Generating a Tracing to see how the simulation works.
1. Click the Stimulate button once. The voltage is at 0 so no tracing should result.
2. Increase the voltage to 3.0 using the + button. Click Stimulate again and a
tracing should appear.
3. To keep the data, click on Record Data. We are only interested in active force
at this time.
4. To clear the screen, Click on Clear Tracings on the oscilloscope.
Investigating Graded Muscle Response to Increased Stimulus Intensity
Directions for the Simulation
1. Clear any tracings on the oscilloscope.
2. Set the voltage at 0.0 V and click Stimulate.
3. Record data.
4. Increase the voltage by 0.5 V, stimulate and record data.
5. Continue to increase the voltage by 0.5V increments, stimulating the muscle each
time and recording the data. Do this until you reach 10 V, recording the data at
each step.
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What was the minimal or threshold stimulus? ____________volts
What was the maximal stimulus? _____________volts
What did you keep constant in this experiment?
Circle one.
Voltage
Frequency
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What did you vary? Circle one.
Voltage
Frequency
6. Under the Tools menu, select Print Data. Give the document a name that you
will recognize, and then hit OK.
7. Print the data from this simulation.
8. Use this data to construct a graph on the attached graph paper. Do not use a
computer-generated graph. Construct the graph as follows:
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Active Force should be on the Y-axis and Voltage on the X-axis.
Be sure to label the axes and include units – Voltage is in volts,
Force is in grams.
Label minimal or threshold stimulus and maximal stimulus.
This graph is Figure 1. Give the graph a meaningful title. A
suggested title is The Relationship Between Increase in Voltage and
Force of Contraction in Skeletal Muscle. Put this title below the
graph after the Figure 1 label.
9. Think about how you determined threshold stimulus and then devise an
experiment to determine a more accurate minimal or threshold stimulus.
Describe how you will set up and conduct the experiment. Include what you
will vary and what you will hold constant in your description. 3 points.
________________________________________________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________
10. Carry out your experiment.
Record the more accurate minimal or threshold stimulus. __________volts.
Questions
1. Why didn’t you see a response with a voltage of .5 volts?
_____________________________________________________________
2. Why did increasing the voltage from 3 volts to 4 volts increase the force of
contraction?
_____________________________________________________________
3. After what voltage did increasing the voltage not cause an increase in
contraction force? ____________________
4. Explain why increased voltage after this point did not increase force.
_____________________________________________________________
5. What type of summation is this?
______________________________________________________________
Investigating Wave Summation and Tetanus
Directions:
1. To Continue - Select Multiple Stimulus from the Experiment menu at the top
of the screen.
2. Clear Tracings. Set the voltage at 8.2V and the muscle length at 75mm. Do not
change this throughout this part of the experiment.
3. Click Single Stimulus, and then click it again quickly, before the muscle has
had a chance to relax. Observe whether the second contraction produces a
greater force.
Is the peak force produced in the second contraction greater than that produced
by the first stimulus? ________
4. Under Tools, choose Print Graph, give the graph a name, and print a graph of
the experiment. Label this graph Figure 2. Single Stimulus First Try
5. Try again and increase the frequency of the stimuli. Observe what happens.
Is the total force production even greater with increased frequency of
stimulation?
___________
The same number of motor units is being stimulated (voltage is constant). Why
is the force of the second contraction greater than that of the first contraction?
6. Under Tools, choose Print Graph, give the graph a name and print a graph of
the experiment. Label the graph Figure 3. Single Stimuli, Increased Frequency
7. What did you keep constant in this experiment? Circle one
Voltage
Frequency
8. What did you vary? Circle one
Voltage
Frequency
Investigating Fusion Frequency/Tetanus.
1. Clear Tracings. Set the voltage at 8.2V and the muscle length at 75mm. Do not
change this throughout this part of the experiment.
2. Set the stimulus rate to 30 stimuli per second.
3. Click Multiple Stimulus.
4. Click Stop Stimulus when the tracing reaches the 120 msec line on the screen..
5. Click Record Data.
6. Increase the stimulus rate by 10 stimuli/second and repeat. Record Data.
7. Repeat until you reach a stimulus rate of 150 stimuli/second. Record Data each
time.
How do the tracings change in appearance as the stimulus rate is increased?
________________________________________________________________
________________________________________________________________
8. When you have finished, click Tools and Print Graph. Print a copy of this graph
for each member of your group to turn in. Label the graph Figure 4.
Investigating Fusion Frequency/Tetanus
9. From your graph estimate the stimulus rate above which there appears to be no
significant increase in force (this occurs at fused tetanus) and record here.
_________ stimuli per second.
Questions
1. Why did the response begin to smooth out as the frequency of stimuli
increased?
2. ________________________________________________________________
________________________________________________________
3. What type of summation is this?
_______________________________________
4. What is the term used when the response becomes a smooth rather than wavy
response? _________________________
5. Think about how might you produce smooth contractions at a lower force than
the force you observed with the smooth contractions in this activity. Think
about Multiple Motor Unit summation as you set up the experiment.
What is your hypothesis?
________________________________________________________________
________________________________________________________________
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What will you vary? ______________________________________________
What will you hold constant (in addition to muscle length)? Remember to keep
all but one variable constant. _________________________
6. Conduct the experiment to test your hypothesis. Record Data.
What did you observe?__________________________________________
_____________________________________________________________
7. When you have finished, click Tools and Print Graph. Print a copy of this
graph for each member of your group to turn in. Label this graph Figure 5.
Smooth Contractions at a Lower Force.
Summary and Questions – Exercise 16B
1. A graded contraction is a smooth contraction that can vary in force. Explain
how you incorporated information from these activities to produce an example
of graded contractions? Include in your answer how you produced a smooth
contraction, and how you were able to vary the strength of the contraction. 2
points.
2. Define:
 Muscle twitch
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Latent period
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Period of contraction
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Period of relaxation
3. Draw a twitch contraction that has a latent period of 2msec, a contractile
period of 8 msec. with a maximum force of 2 g., and a relaxation period of 10
msec. Use the graph below. Label latent period, period of contraction and
period of relaxation. Label as Figure 6. Muscle Twitch.
8 points.
Stimulus
Figure 6. _________________________________________________
Hand in for a grade at the next class, stapled together IN THIS ORDER:
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

Lab 8 Sheet with questions answered.
Summary and Questions Sheet
Printed data from Activity 3 Labeled Table 1. Multiple Motor Unit
Summation above the table. 10 points.
Hand-plotted graph from Activity 3. Label Figure 1 below the graph. 10
points
Activity 5 - two labeled computer-generated graphs (from 4. and 6.). Label
Figure 2 and Figure 3 below the graphs. 10 points.
Activity 6- two labeled computer generated data plots (one from 8. and one
from 12.). Label Figure 4 and Figure 5 below the graphs. 10 points
Figure 1. ____________________________________________________
Title
Figure 1 . ____________________________________________________
Title
For the Lab Exam
Computer Simulation
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Interpret data from the skeletal muscle computer simulation.
Interpret data from unfused tetanus, recruitment and fatigue experiment.