Problem Set 3 - Muscle Function


Problems/Conference #3

Practice Multiple Choice Questions

Muscle function

 

 

Use the following graph for the following three questions. In this graph, active tension that is developed by a muscle during contraction is measured at several different initial lengths of the muscle. The same supramaximal electrical stimulus is used to induce each contraction, and the muscle is loaded enough so that it does not shorten during the contraction; i.e. the contraction is isometric.

 

SELECT THE LETTER THAT CORRESPONDS BEST TO THE STATEMENT.

 

1. When the muscle is stimulated, no overlap of the actin and myosin filaments occurs.

 

2. Optimum overlap of the actin and myosin filaments occurs during the contraction.

 

3. Total tension (active plus passive) is not shown on the graph. If it were shown, it would be greatest at a length corresponding to which letter?

 

 

In the following figure, velocity of shortening is plotted as a function of the load against which the muscle contracts. The initial length of the muscle was the same for each contraction, and the muscle was stimulated by direct application of an electrical current to the muscle fiber. Use this figure to answer the next three questions.

 

 

 

4. At a load corresponding to which letter on the bold curve is the muscle performing the most external work?

 

5. At which letter is the contraction of the muscle an isometric contraction?

 

6. After an experimental treatment, the muscle that originally followed the relationship shown by the upper (bold) curve now follows the relationship shown by the lower curve. The most likely treatment was:

 

 

 

 

 

 

 

7. All of the following are involved in producing graded contractions of an entire muscle EXCEPT:

 

8. Which one of the following comparisons of red and white muscles is correct?

 

INSTRUCTIONS FOR QUESTIONS 9-11: Match the muscle with a characteristic (or characteristics) that is (are) UNIQUE to that muscle type ALONE.

 

9. Skeletal muscle

10. Cardiac muscle

11. Smooth muscle

CHARACTERISTIC:

 

12. Which of the following is/are involved in the production of a tetanic contraction?

 

13. Which one the following statements regarding skeletal muscle contraction is correct?

 

14. All of the following statements regarding the contraction of smooth muscle are true EXCEPT one. Which one is false?

 

15. Contraction of all three muscle types (skeletal, cardiac, and smooth muscle) have which one of the following in common:

 

16. From the list of three statements (I-III) concerning the rate of myosin ATP hydrolysis in skeletal muscle, select the combination that is correct?

ATP hydrolysis:

I = is close to zero when the muscle contracts against a very heavy (isometric) load.

II = depends on the level of myosin phosphorylation.

III = determines how fast the muscle shortens.

 

17. Which of the following statements regarding smooth muscle is/are correct?

I = Once phosphorylated-myosin has attached to actin, actin can remain attached to myosin even when myosin get dephosphorylated.

II = Contraction can occur in the absence of action potentials.

III = The source of to produce contraction is entirely extracellular.

 

18. The concentration of free Ca2+ in the cytoplasm of a skeletal muscle is very low (Ca2+ = 0.1 µM), while the concentration of ATP may be zero or normal. Which letter BEST represents the contractile state of this muscle?

Zero ATPNormal ATP
A.contractedcontracted
B.relaxedrelaxed
C.contractedrelaxed
D.relaxedcontracted

 

19. The concentration of free Ca2+ in the cytoplasm of a skeletal muscle is high (Ca2+ = 10 µM), while the concentration of ATP may be zero or normal. Which letter BEST represents the contractile state of the muscle?

Zero ATPNormal ATP
A.contractedcontracted
B.relaxedrelaxed
C.contractedrelaxed
D.relaxedcontracted