Lab 9
Skeletal Muscle Physiology
PhysioEx Exercise
16B or in Mastering
A&P Chapter 9
Assignment - Skeletal Muscle Physiology
Use directions in handout. This PhysioEx experiment is located in the back
of the lab manual on page PEx-23 or can be accessed on Mastering A&P,
Chapter 9 – Skeletal Muscle Physiology.
Hand in for a grade at the next class, stapled together IN THIS ORDER:
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Exercise 16B 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 (Figure 1) 10 points
Activity 5 - two labeled computer-generated graphs (from 4. and 6.) Figures
2 and 3 10 points.
Activity 6- two labeled computer generated data plots (one from 8. and one
from 12.) Figures 4, and 5 10 points
Name______________________
Lab Section ________________
Microscopic Anatomy and Organization of Skeletal Muscle and Muscle
Physiology
Lab 9
Skeleton Muscle Physiology: Computer Simulation
Exercise 16B - Page PEx-23
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.
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.
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.
Turn to the exercise Skeletal Muscle Physiology: Computer Simulation in
your lab manual - PagePEx-23. Note: Exercise 16B is in the back of the lab
manual or ask for a handout from the front desk.
These directions are taken from the lab manual and slightly modified for our
use.
Open PhysioEx and Choose Exercise 2:Skeletal Muscle Physiology from the
menu at the top of the screen. Then choose Single Stimulus. The screen should
look like Figure 16B.1 in the Lab Manual. 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.
Activity 1: 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.
Activity 3: 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
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What was the maximal stimulus? _____________volts
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What did you keep constant in this experiment? Circle one
Voltage
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Frequency
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 Activity 3.
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.
Give the graph figure a meaningful title. A suggested title is “The
Relationship Between Increase in Voltage and Force of Contraction
in Skeletal Muscle” Put this below the graph, labeled Figure 1.
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.
________________________________________________________________
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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.
At what point did increasing the voltage not cause an increase in
contraction force? ____________________
4.
Explain why increased voltage after this point did not increase
contraction force.______________________________________________
_____________________________________________________________
5.
What type of summation is this?
______________________________________
Activity 5: 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 Stimuli 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
Activity 6: 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. 10. Think about how might you produce smooth contractions at a lower force
than the force you observed with the smooth contractions in Activity 6. (Hint:
think about Activity 3 when answering this question.) Answer the questions
below to describe how you will set up and conduct the experiment.
 What is your hypothesis?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
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What will you vary?
_______________________________________________
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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 both Activity 3 and Activity 6 to
produce examples 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. _________________________________________________
Figure 1. ____________________________________________________
Title
Figure 1 . ____________________________________________________
Title