Question 1

Which of the following best describes the structural difference between smooth, cardiac, and skeletal muscle cells?

Accepted Answer

Smooth muscle cells are spindle-shaped with a single nucleus and lack striations, cardiac muscle cells are branched and striated with intercalated discs, and skeletal muscle cells are multinucleate, striated, and cylindrical.

Question 2

During muscle contraction, which bands or zones of the sarcomere decrease in width?

Accepted Answer

The H zone and I band

Question 3

Which protein is responsible for anchoring the thick myosin filaments in the sarcomere and runs from Z line to Z line?

Accepted Answer

Titin

Question 4

What is the primary function of the sarcoplasmic reticulum in skeletal muscle cells?

Accepted Answer

To store and release calcium ions ($$Ca^{2+}) $$during muscle contraction

Question 5

Which sequence correctly describes the steps of the contractile cycle in skeletal muscle?

Accepted Answer

Myosin binds ATP, hydrolyzes ATP to ADP and $$P_i$$, binds actin, releases ADP and $$P_i$$, power stroke, binds new ATP and releases actin.

Question 6

Which of the following statements about motor units is correct?

Accepted Answer

A motor unit consists of one motor neuron and all the muscle fibers it innervates.

Question 7

Which muscle fiber type is best suited for endurance activities such as marathon running?

Accepted Answer

Type I red fibers (slow oxidative)

Question 8

What effect does curare have on muscle contraction?

Accepted Answer

It blocks acetylcholine receptors, preventing muscle contraction and causing paralysis.

Question 9

Botulinum toxin (Botox) causes muscle paralysis by:

Accepted Answer

Blocking acetylcholine release at the neuromuscular junction.

Question 10

Which of the following is TRUE regarding the role of calcium ions ($$Ca^{2+}) in $$muscle contraction?

Accepted Answer

$$Ca^{2+}$$ binds to troponin, causing a conformational change that exposes myosin binding sites on actin.

Question 11

Which of the following best explains why skeletal muscle contraction is under voluntary control?

Accepted Answer

Skeletal muscle fibers are innervated by motor neurons that are controlled by conscious signals from the central nervous system.

Question 12

Which of the following is a real-world consequence of botulinum toxin contamination in food?

Accepted Answer

Botulinum toxin can cause paralysis and death by preventing acetylcholine release, as seen in historical outbreaks from improperly canned foods.

Question 13

Which of the following best describes the mechanism of rigor mortis?

Accepted Answer

Rigor mortis occurs because ATP is no longer available to release myosin from actin, causing muscles to remain contracted.

Question 14

Which of the following is a characteristic of cardiac muscle that distinguishes it from skeletal muscle?

Accepted Answer

Cardiac muscle cells are branched and connected by intercalated discs, allowing rapid spread of depolarization.

Question 15

Which of the following best describes the role of T-tubules in skeletal muscle contraction?

Accepted Answer

T-tubules transmit action potentials deep into the muscle fiber, triggering calcium release from the sarcoplasmic reticulum.

Question 16

Which of the following is TRUE about antagonistic muscle pairs?

Accepted Answer

One muscle contracts while the other relaxes, allowing movement around a joint.

Question 17

Which of the following best explains the difference between temporal and spatial summation in muscle contraction?

Accepted Answer

Temporal summation is increased frequency of stimulation of a single fiber, while spatial summation is increased number of motor units activated.

Question 18

Which of the following is a physiological adaptation seen in muscles after regular aerobic exercise?

Accepted Answer

Increased density of capillaries, myoglobin content, and number of mitochondria in muscle fibers.

Question 19

Which of the following statements about muscle contraction is correct?

Accepted Answer

Muscle contraction occurs when actin and myosin filaments slide past each other, shortening the sarcomere.

Muscle Structure and Function in Vertebrates

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