Section Test:Muscle Cells

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This Section Test deals with muscle fibers and cells and the biochemistry of muscle contraction. Please see The Muscle Cell for the review text related to this section test.

Section Test

1. Which of the following best describes muscle contraction?

Actin and Myosin filaments shorten to slide past each other.
As they slide past each other, actin filaments shorten, while myosin filaments do not shorten
Actin and myosin filaments do not shorten, but rather, slide past each other.
As they slide past each other, myosin filaments shorten, while actin filaments do not shorten.
→ Neither Actin filaments nor myosin filaments change length during contraction. Instead, they are forced to slide past each other reducing the spacing between them. Thus the overall length of the repeating units gets shorter, but the different types of filaments themselves do not change in length.

2. What is the role of Ca++ in muscle contraction?

It binds to tropomyosin, leading to the exposure of myosin-binding sites on actin filaments
It binds to myosin, promoting the cleavage of ATP and the change of chemical energy into movement of the myosin head.
It binds to troponin, leading to the exposure of myosin-binding sites on actin filaments.
It binds to troponin, leading to the release of ATP from the sarcoplasmic reticulum (SR).

3. Which of the following is NOT true?

A single action potential at the neuromuscular junction is sufficient to cause a muscle to twitch.
Once maximum muscle tension is achieved, no ATP is required to maintain that level of tension.
An action potential in the muscle cell activates contraction by releasing Ca++ into the sarcoplasm.
Summation of twitches leads to a graded increase in the tension that can be generated by a single muscle fiber.

4. The striated appearance of skeletal muscle is due to the?

dark color of myosin.
multiple nuclei per fiber.
regular arrangement of filaments.
dense array of microtubules.

5. An individual sarcomere unit consists of

a stack of actin fibers.
overlapping actin and membrane.
overlapping myosin and membrane.
overlapping actin and myosin.

6. How do muscle fibers shorten during contraction?

Individual protein filaments contract.
More cross-bridges are formed between filaments.
Arrays of filaments overlap each other.
Protein filaments coil more tightly.

7. How do actin and myosin molecules interact?

Globular myosin heads bind to actin filaments.
Globular actin heads bind to myosin filaments.
Myosin filaments bend to connect to actin.
Actin filaments bend to connect to myosin.

8. Which of the following events does not occur during muscle contraction?

The distance between Z lines increases.
The sarcomere shortens.
The H zone is reduced.
The I band is reduced.

9. Which of the following statements about the molecular arrangement of actin and myosin in myofibrils is false?

A thin filament consists of actin and tropomyosin.
Two chains of actin monomers are twisted into a helix.
Two strands of tropomyosin lie in the grooves of the actin.
Troponin forms the head of the myosin molecule.

10. Starting with the arrival of an action potential at the neuromuscular junction, which of the following is the correct order of events?

Calcium is released from the sarcoplasmic reticulum, an action potential travels down the T tubules, depolarization spreads through the T tubule, and myosin binds actin.
An action potential travels down the T tubules, depolarization spreads through the T tubule, calcium is released from the sarcoplasmic reticulum, and myosin binds actin.
An action potential travels down the T tubules, depolarization spreads through the T tubule, calcium is taken up by the sarcoplasmic reticulum, and myosin binds actin.
An action potential travels down the T tubules, depolarization spreads through the T tubule, ATP binds to myosin, and myosin binds actin.

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