PhysioEx 8.0 Skeletal muscle Physiology

One or two questions per thread, thank you.

I found these on another website because i was having troubles too. Hope this helps you some!


Electrical Stimulation
1. Name each phase of a typical muscle twitch, and, on the following line, describe what is happening in each phase.
a. Latent-stage from rest to muscle tension begins

b. Contraction-At this stage the muscle reaches its peak in contraction

c. Relaxation- muscle is shortened, returns to zero and back initial length.

2. In Activity 2, how long was the latent period? ___2.2_______ msec
Describe the chemical changes that are occurring during this period.
Calicum levels are low since muscle contaction is not at its peak. Preparing for the the contraction Ca begin the process of sending Acetychlorine binding to the Sacroplasma

The Graded Muscle Response to Increased Stimulus Intensity
3. From Activity 3, describe the effect of increasing the voltage. What happened to the force generated and why did this change occur? Higher voltage results in higher force and a higher contractile force


4. How does this change occur in vivo?Tthe more stimulus of muscle require more work on the cells which requires more Ca+2 to facilitate this stimulus increase.

5. In Activity 4, you looked at the effect of stimulating the muscle multiple times in a short period with complete relaxation between the stimuli.
Describe the force of contraction with each subsequent stimulus. The force of contraction is higher with each subsequent stimulus.

6. Describe the chemical changes that are thought to correlate to this change in vivo. this requires more Ca+2 in the sacroplasm and more activity on the thin filament for cross-bridge attachments.

7. In Activity 5, what was the effect of increasing the frequency of stimulation?   Increase frequency of stimuli result in increased muscle tension.

8. Compare and contrast wave summation with recruitment (multiple motor unit summation). How are they similar? How was each achieved in the simulation?   They...

Which website was it?

8. Compare and contrast wave summation with recruitment (multiple motor unit summation). How are they similar? How was each achieved in the simulation? Motor recruitment involves sending signals to multiple parts of the muscle at once, resulting in one quick, strong contraction. Summation is similar in that it increases contractile force. Summation is achieved by increasing frequency of stimulation. Recruitment is achieved by increasing force of stimulation.


9. Explain how wave summation and recruitment are achieved in vivo. Summation is achieved
 by the nervous system increases firing rate of motor neurons. Recruitment is caused by neural
activation of increasingly large numbers of motor units serving the muscle.


10. For Activity 6, explain how you were able to achieve smooth contraction at a given force level. Smooth contractions at a given force level are obtained by increasing the force of stimulation for a high force level or decreasing the force of stimulation for a low force level.

11. In Activity 7, explain why the force of the muscle decreased over time during uninterrupted stimulation. Describe the multiple causes of this phenomenon, which occurs in vivo with prolonged use of a muscle. Muscle fatigue occurs where muscle cells ATP consumption is faster than it's produce thus fewer ATP less energy to maintain or increase contraction.


Isometric Contraction
12. In Activity 8, at what length of the muscle does the passive force start to increase? 80

13. Explain what happens to the active force with an increase in the muscle length. Force decreases as muscle length is increased beyond the optimal length. The muscle has two different fibers, actin and myosin. They pull on each other to contract the muscle. As the muscle length increases less of these fibers are in contact with each other, decreasing the force the muscle can create.

14. Explain what happens to the active force with a decrease in the muscle length. Active force decreases when the muscle length is increased.

15. Explain what is happening in the sarcomere that results in the changes in total force when the muscle length changes. Sarcomere length changes and causes unwanted changes in the interaction between these two fibers.

Isotonic Contraction
16. In Activity 9, which weight resulted in the highest initial velocity of shortening? 0.5 grams

17. Explain the relationship between the amount of resistance and the initial velocity of shortening. If there is more resistance on a muscle it will not be able to contract as fast as the muscle with less resistance.

18. Explain why it will take you longer to perform 10 repetitions lifting a 20-pound weight than it would to perform the same number of repetitions with a 5-pound weight. The lighter the weight the faster the muscle can contract because it has less resistance.