Question 1

Which of the following best describes the primary function of the sarcoplasmic reticulum (SR) in skeletal muscle fibers?

Accepted Answer

It stores and regulates intracellular levels of $$\mathrm{Ca$$^{2+}$$}.$$

Question 2

What is the role of terminal cisterns in the sarcoplasmic reticulum?

Accepted Answer

They store large amounts of $$\mathrm{Ca$$^{2+}$$}$$ near the A band-I band junctions.

Question 3

T tubules are essential for muscle contraction because they:

Accepted Answer

Allow electrical signals to penetrate deep into the muscle fiber.

Question 4

Which of the following sequences correctly describes the process by which an electrical impulse leads to $$\mathrm{Ca$$^{2+}$$}$$ release in skeletal muscle fibers?

Accepted Answer

Electrical impulse $$\rightarrow T $$tubule voltage sensor proteins change shape $$\rightarrow SR $$proteins change shape $$\rightarrow$$ $$\mathrm{Ca$$^{2+}$$}$$ release

Question 5

If a mutation caused the T tubule voltage sensor proteins to lose their ability to change shape, what would be the most likely consequence for muscle contraction?

Accepted Answer

The sarcoplasmic reticulum would not release $$\mathrm{Ca$$^{2+}$$}$$, preventing contraction.

Question 6

Which structural feature increases the surface area of the muscle fiber and allows rapid transmission of action potentials into the cell interior?

Accepted Answer

T tubules

Question 7

During muscle contraction, which event occurs immediately after the T tubule voltage sensor proteins detect an action potential?

Accepted Answer

SR proteins change shape, opening $$\mathrm{Ca$$^{2+}$$}$$ channels.

Question 8

A patient has a genetic defect that prevents the formation of terminal cisterns in their skeletal muscle. Which of the following would most likely be observed?

Accepted Answer

Reduced storage and release of $$\mathrm{Ca$$^{2+}$$}$$, leading to weak muscle contractions.

Question 9

Which of the following best explains why T tubules are positioned between terminal cisterns to form a triad?

Accepted Answer

To ensure rapid and coordinated release of $$\mathrm{Ca$$^{2+}$$}$$ throughout the muscle fiber.

Question 10

Which of the following is a direct result of the interaction between T tubule voltage sensor proteins and SR membrane proteins?

Accepted Answer

Opening of $$\mathrm{Ca$$^{2+}$$}$$ channels in the SR.

Question 11

A researcher blocks the function of the integral membrane proteins in the SR cisterns. What is the most immediate effect on muscle physiology?

Accepted Answer

Failure to release $$\mathrm{Ca$$^{2+}$$} in $$response to an action potential.

Question 12

Which of the following best describes the relationship between the sarcoplasmic reticulum and T tubules in skeletal muscle fibers?

Accepted Answer

T tubules transmit action potentials deep into the fiber, triggering the SR to release $$\mathrm{Ca$$^{2+}$$}.$$

Question 13

Which of the following would most likely occur if the T tubules were absent from a skeletal muscle fiber?

Accepted Answer

Action potentials would not reach the interior of the fiber, impairing $$\mathrm{Ca$$^{2+}$$}$$ release and contraction.

Question 14

Which of the following is NOT a function of the sarcoplasmic reticulum in skeletal muscle fibers?

Accepted Answer

Synthesis of acetylcholine for neuromuscular transmission.

Question 15

In a laboratory experiment, a toxin selectively blocks the voltage sensors in the T tubule membrane. Which step in muscle contraction would be directly affected?

Accepted Answer

Release of $$\mathrm{Ca$$^{2+}$$}$$ from the sarcoplasmic reticulum.

Question 16

Which of the following best explains why the triad structure (T tubule flanked by two terminal cisterns) is critical for muscle contraction?

Accepted Answer

It ensures that $$\mathrm{Ca$$^{2+}$$}$$ release is synchronized with the arrival of the action potential.

Sarcoplasmic Reticulum and T Tubules in Skeletal Muscle Fibers

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