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Problem Set 3 - Muscle Function

Page history last edited by PBworks 14 years, 1 month ago

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:

  • A. lowering the concentration of extracellular Ca2+.
  • B. partial blockade of the Ca2+ ATPase pump on the sarcoplasmic reticulum that removes Ca2+ from the cytoplasm.
  • C. partial blockade of the motor end plates with curare.
  • D. a drug was given that decreased the activity of the myosin-ATPases in the muscle.

 

 

 

 

 

 

 

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

  • A. contraction of only a portion of the muscle fibers within a single motor unit during a finely graded movement.
  • B. motor units with a high motoneuron to fiber ratio are utilized for fine movements; motorneurons with a low motorneuron to muscle fiber ratio are utilized for gross movements .
  • C. discharging many motor units at one time (spatial recruitment) allows increased force to be generated.
  • D. discharging individual motor units at a more rapid rate (temporal recruitment) allows increased force to be generated
  • E. simultaneous spatial and temporal recruitment of motor units during gross movements.

 

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

  • A. myoglobulin content: white > red.
  • B. capacity to maintain a contraction: white > red.
  • C. rate at which contraction develops following stimulation: red > white
  • D. aerobic metabolic capacity: red > white.
  • E. proportion of fibers in the extraocular muscles: red > white.

 

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:

  • A. graded force generation can occur in response to graded changes in membrane potential.
  • B. possess a "funny" slow inward Na+ current that is activated by hyperpolarization.
  • C. presence of striations.
  • D. receptors at the junction between the nerve and the muscle are nicotinic cholinergic.
  • E. sliding of myosin filaments on actin produces shortening of the muscle.
  • F. membrane dihydropyridine receptors work mainly as voltage sensors instead of as Ca2+ channels.

 

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

  • A. increasing the stimulating voltage to a greater amplitude than that which normally produces a maximum twitch of the muscle.
  • B. rapid stimulation of the muscle initiates a new contraction before the series elastic elements have returned to their resting tension.
  • C. rapid stimulation of the muscle adds new Ca2+ to the cytosol before the ATPase pump on the sarcoplasmic reticulum has removed all of the Ca2+ that entered during the last contraction.
  • D. A and B are correct.
  • E. B and C are correct.
  • F. A and C are correct.

 

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

  • A. Short thick muscles develop less force during a maximum contraction than do long slender muscles.
  • B. Long slender muscles shorten less rapidly during a maximum contraction than do short thick muscles.
  • C. The velocity of shortening of a muscle is inversely proportional to the load the muscle is moving during the contraction.
  • D. Neurotransmitters or hormones that increase the intracellular concentrations of cAMP (or cGMP) induce relaxation.

 

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

  • A. Large rapid changes in membrane potential characterize the action potentials.
  • B. Ca2+, calmodulin, and myosin light chain kinase are involved in the activation of myosin light chain.
  • C. Smooth muscle contraction can be initiated by stretch-activated ion channels, by neurotransmitters, or by hormones.
  • D. Neurotransmitters or hormones that increase the intracellular concentration of cAMP within smooth muscle inhibit contraction.
  • E. Neurotransmitters or hormones that increase the activity of cGMP within smooth muscle inhibit contraction.

 

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

  • A. activation of a myosin light chain kinase.
  • B. an absolute requirement for extracellular Ca2+.
  • C. electrical coupling between cells through gap junctions.
  • D. phosphorylation of myosin modulates the contraction.
  • E. an increase in cytoplasmic Ca2+ concentration as a prerequisite for contraction.

 

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.

  • A. I, II and III are correct.
  • B. Only II is correct.
  • C. Only II and III are correct.
  • D. Only I and III are correct.
  • E. Only I is correct.

 

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.

  • A. Only I and II are correct.
  • B. Only II and III are correct.
  • C. I, II and III are correct.
  • D. Only III is correct.
  • E. Only II is correct.

 

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

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