VIRTUAL MUSCLE STIMULATION ACTIVITY
Go to: http://glencoe.mcgraw-hill.com/sites/dl/free/0078757134/383958/BL_21.html
Read the Purpose and Objectives of the activity. Click on the blue Information button
on the bottom right. Answer the following questions:
1. Contrast voluntary and involuntary muscles. Include what types of muscles are in
each category and where these muscles are found.
Both cardiac and smooth muscles are called “involuntary” because their contractions
cannot be consciously controlled. Cardiac muscle exists only in the heart and contracts
approximately 70 times per minute to pump blood throughout a body's circulatory
system. Smooth muscles line many internal organs such as the trachea, intestines, and
bladder. Smooth muscles contract and relax slowly, exerting and releasing pressure on
the organs they surround. Skeletal muscles are the muscles that are used for
movement. They are called “voluntary” muscles because their contractions are
consciously controlled.
2. What attaches muscle to bones? Tendons
3. What is the “all or none” law of muscle contraction? When exposed to stimuli from
the nervous system, each individual muscle fiber will contract either completely or not
at all.
4. How is the strength of the muscle contraction determined? By the number of
individual muscle fibers that respond to a stimulus.
5. Define a muscle twitch: If a single, quick electrical stimulus is applied to a skeletal
muscle, the muscle will respond by contracting and relaxing quickly.
6. Define a muscle’s “threshold of stimulation:” The weakest electrical stimulation
(measured in volts) required to cause a muscle to twitch.
7. Define the “point of muscle overload:” As the workload on a muscle increases, the
muscle will eventually reach a point at which it will no longer be able to contract, no
matter how much electrical stimulation it receives.
Finish reading the information and then close the Information window. Follow the
Procedure and record your data in the Table below. After you finish the experiment,
answer the Analysis questions.
TABLE 1 – Threshold Stimulus (V)
LOAD
LOWER
FORELIMB
MUSCLES
UPPER
FORELIMB
MUSCLES
CALF MUSCLES
THIGH
MUSCLES
0g
2.0
3.0
5.0
6.0
5g
3.0
4.0
5.5
6.5
10g
4.0
5.0
6.0
7.0
20g
none
7.0
7.0
8.0
40g
none
None
8.0
9.0
80g
none
none
none
10.0
ANALYSIS:
1. Based on the results of your investigation, what conclusions can you draw about the
relationship between a muscle's workload and its threshold of stimulation?
As the load doubles, the threshold stimulus usually increases by 1. A muscle that has a
higher threshold of stimulation with no workload can handle a much higher workload.
2. Why would a muscle's threshold of stimulation change as its Workload changes?
It would require more stimulation in order to contract. The muscle essentially has to
work harder to get a contraction.
3. Which muscles were able to contract under the greatest loads? What does this
suggest about the role these muscles play in frog movement?
The calf and thigh muscles could contract with the greatest loads. These muscles are
required for the frog to leap and need to bear the weight of the frog while causing the
frog to jump.
4. Describe an experiment you might perform to determine which leg muscles of a frog
are important for jumping long distances.
Answers will vary.
5. What are some advantages of performing this experiment in a simulated
environment?
Each muscle can be isolated easily and a simulation does not hurt the animal.