Question 1

Which of the following best describes the functional contractile unit of a skeletal muscle fiber?

Accepted Answer

Sarcomere

Question 2

During skeletal muscle contraction, which band or zone does NOT change in length?

Accepted Answer

A-band

Question 3

What is the primary role of calcium ions ($$\mathrm{Ca$$^{2+}$$}) in $$the molecular mechanism of skeletal muscle contraction?

Accepted Answer

To bind to troponin and expose myosin-binding sites on actin

Question 4

Which protein forms the thick filaments in skeletal muscle and is responsible for the power stroke during contraction?

Accepted Answer

Myosin

Question 5

A patient is experiencing muscle stiffness after death (rigor mortis). What is the molecular cause of this phenomenon?

Accepted Answer

Depletion of ATP preventing myosin head detachment from actin

Question 6

Which of the following correctly describes the sequence of events in the sliding filament theory of muscle contraction?

Accepted Answer

Calcium binds to troponin, tropomyosin shifts, myosin binds to actin, power stroke occurs

Question 7

Which of the following is TRUE regarding the structure of thin filaments in skeletal muscle?

Accepted Answer

They consist of F-actin polymers and regulatory proteins such as troponin and tropomyosin

Question 8

If ATP is not available in a muscle cell, which step of the cross-bridge cycle will be directly affected?

Accepted Answer

Detachment of myosin head from actin after the power stroke

Question 9

Which of the following best explains why calcium and ATP are both required for muscle contraction?

Accepted Answer

Calcium binds to troponin to expose myosin-binding sites, and ATP is needed for myosin head movement and detachment

Question 10

A researcher measures the length of the sarcomere before and after contraction. Which of the following changes would be expected?

Accepted Answer

The distance between Z-lines decreases

Question 11

Which of the following events occurs FIRST during excitation-contraction coupling in skeletal muscle?

Accepted Answer

Binding of acetylcholine to nicotinic receptors at the neuromuscular junction

Question 12

Which equation correctly represents the hydrolysis of ATP during muscle contraction?

Accepted Answer

$$\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{Pi}$$

Question 13

Which of the following statements about myofibrils is CORRECT?

Accepted Answer

Myofibrils are composed of repeating units called sarcomeres

Question 14

A mutation prevents troponin from binding calcium. What is the most likely consequence for muscle contraction?

Accepted Answer

Tropomyosin will not shift, preventing myosin from binding actin

Question 15

Which of the following is a direct result of the power stroke in the cross-bridge cycle?

Accepted Answer

Movement of actin filaments toward the center of the sarcomere

Question 16

Which structure in skeletal muscle is responsible for storing and releasing calcium ions during contraction?

Accepted Answer

Sarcoplasmic reticulum

Question 17

Which of the following best describes the role of tropomyosin in muscle contraction?

Accepted Answer

It blocks myosin-binding sites on actin in the absence of calcium

Question 18

Which of the following is TRUE regarding the organization of skeletal muscle?

Accepted Answer

Muscle fibers are organized into fascicles, which are grouped to form the whole muscle

Question 19

A muscle cell is exposed to a toxin that prevents ATP synthesis. Which of the following would occur during contraction?

Accepted Answer

Myosin heads would remain attached to actin, causing muscle rigidity

Question 20

Which of the following is a correct statement about the relationship between myofibrils, myofilaments, and sarcomeres?

Accepted Answer

Myofibrils are composed of repeating sarcomeres, which contain myofilaments

Skeletal Muscle Structure and Contraction: Anatomy & Physiology Study Notes

Study Guide - Practice Questions