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Lab 9
Microscopic Anatomy and Organization of Skeletal Muscle - Exercise 14
Skeletal Muscle Physiology
Assignment - Microscopic Anatomy and Organization of Skeletal Muscle
Activity 1: Examining Skeletal Muscle Cell Anatomy
Be sure you can identify striations, nuclei, axons and axon terminals,
muscle cells or fibers. (Plate 2 and Figure from Exercise 6).
Activity 2: Examining the Histological Structure of Skeletal Muscle
Activity 3: Studying the Structure of the Neuromuscular Junction (Plate 4)
Identify axon, axon terminal, and skeletal muscle cell
Assignment – Movie on Muscle and Muscle Contraction
Log in to Massasoit onDemand from the MCC home page
http://www.massasoit.mass.edu/
Select Course Media
Select Linda Kollett Anatomy and Physiology
Login using your Banner login and password
Select Anatomy and Physiology Muscle Movie Video
Select Antatomy and Physiology Video Series Muscle Movie – be patient, it
takes time to load and may have to buffer periodically.
Watch the movie and answer the questions on the next page.
Note: you should view the movie before coming to Lab 9
Assignment - Skeletal Muscle Physiology – Exercise 16B
Use directions in handout
Name____________________________
Lab Section ________________
Movie on Muscle and Muscle Contraction
1.
2.
3.
What actually provides movement – bones or muscles ? ___________________
The biceps and triceps demonstrate __________ muscle action.
True or False. (circle one) Muscles around the ear have an important function
in humans.
4. True or False ( circle one) Most if not all muscle cells are present in humans a
few months after birth.
5. Skeletal muscle cells are Mutinucleate – Mononucleate (circle one)
6. True or False (circle one) Actin molecules shorten as a fibril contracts.
7. As demonstrated by muscle cells in water, muscle cells require both ATP and
_______________ in order to contract.
8.
A neuron and the cells it controls are called a _____________________ .
9.
Lifting a light object requires More – Fewer – The Same Number of (circle
one) motor units when compared to lifting a heavy object.
10. Tendons are Loosely – Tightly (circle one) attached to muscle and bone.
Microscopic Anatomy and Organization of Skeletal Muscle and Muscle Physiology
1. Using Figures 14.1 and 14.4, arrange the following in order from largest to smallest:
Thin Filament, Myofibril, Fascicle, Muscle Cell or Fiber, Thick Filament
_____________, _____________, ____________, _____________, _____________
2. Obtain slides of skeletal muscle, neuromuscular junction (motor end plate), smooth
muscle and cardiac muscle and review the structures of each. Draw a picture of each
slide below and label where appropriate: striations, branched cells, intercalated disc,
nucleus, axon, and axon terminal (at neuromuscular junction). Use pencil or colored
pencil, a ruler for the leader lines and print the labels.
3. Match the letters on the figure with the terms below.
____ blood vessels
____ bone
____ endomysium
____ epimysium
____ fascicle
____ muscle cell or fiber
____ perimysium
____ tendon
A
B
C
D
E
H
F
G
.
4. What is the basic unit of contraction of muscle called? _____________________
5. When a muscle cell contracts, which bands shorten? (2)
_____________________________
_____________________________
A
B
C
D
E
F
6. Match the letters on the figure with the terms below.
___ A band
___ H band
___ I band
___ M line
___ Thick filament
___ Thin filament
___ Z disc
G
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 My 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. The user name is user and there is no password.
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.
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.
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
Pre-activity questions – use your book and notes to answer these questions:
1. What effect should increased stimulus intensity (increased voltage) have on muscle
response – up to a point? ______________________________________
__________________________________________________________________
2. Why does this occur? ________________________________________________
__________________________________________________________________
3. What is a subthreshold stimulus? _______________________________________
__________________________________________________________________
4. What is threshold or minimal stimulus ? ________________________________
_________________________________________________________________
5. What is maximal stimulus? ___________________________________________
_________________________________________________________________
6. Explain why there is no further increase in strength of contraction if voltage is increased
once maximal stimulus has been reached. ________________________
__________________________________________________________________
__________________________________________________________________
7. What is held constant in this type of experiment?
Voltage
Frequency of stimulus (circle one)
8. What is varied in this type of experiment?
Voltage
Frequency of stimulus (circle one)
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.
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 computergenerated 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 a meaningful title. A suggested title is “The Relationship Between
Increase in Voltage and Force of Contraction in Skeletal Muscle”

What was the minimal or threshold stimulus? ____________

What was the maximal stimulus? _____________
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.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
10. Carry out your experiment.
Record the more accurate minimal or threshold stimulus. ___________
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
Pre-activity questions – use your book and notes to answer these questions:
1. Increasing the frequency of stimulation of a muscle without changing the voltage may
increase the force of contraction. What else happens? _________________
__________________________________________________________________
2. How can you explain this result? ______________________________________
_________________________________________________________________
3. What is held constant in this type of experiment?
Voltage Frequency of stimulus (circle one)
4. What is varied in this type of experiment?
Voltage Frequency of stimulus (circle one)
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.
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?
_________________________
6. Under Tools, choose Print Graph, give the graph a name and print a graph of the experiment.
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 Plot Data. Be sure that the Y-axis is displaying
Active Force and the X-axis is displaying Stimuli/Sec. Click Print Plot to print a copy of this
graph for each member of your group to turn in.
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
a. Why did the response begin to smooth out as the frequency of stimuli increased?
_______________________________________________________________________
_____________________________________________________________
b. What type of summation is this? _______________________________________
c. What is the term used when the response becomes a smooth rather than wavy response?
_________________________
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 t 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. ________________________________________-
11. Conduct the experiment to test your hypothesis. Record Data.
 What did you observe?
______________________________________________________________________
__________________________________________________________
12. When you have finished, click Tools and Plot Data. Be sure that the Y-axis is
displaying Active Force and the X-axis is displaying Stimuli/sec. Click Print Plot to
print a copy of this graph for each member of your group to turn in. Go back to
Tools and select Print Graph and print a copy of the graph for each member of your
group.
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?
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. Be sure to label the axes and
give the graph a title.
_________________________________________________
Hand in for a grade, stapled together IN THIS ORDER:

Movie Answer Sheet

Microscopic Anatomy Activity Sheet

Exercise 19B Sheet with questions answered.
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Summary and Questions Sheet
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Printed data from Activity 3
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Hand-plotted graph from Activity 3
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Activity 5 - two computer-generated graphs (from 4. and 6.)
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Activity 6- three computer generated data plots (one from 8. and two from 12.)