Question 1

Which of the following best describes the main difference between cardiac, smooth, and skeletal muscle cells in terms of structure and control?

Accepted Answer

Cardiac muscle cells are striated and involuntary, smooth muscle cells are non-striated and involuntary, and skeletal muscle cells are striated and voluntary.

Question 2

During muscle contraction, which of the following changes occur within the sarcomere?

Accepted Answer

The H zone and I band narrow, and the Z lines move closer together.

Question 3

Which protein is responsible for anchoring the thin filaments to the Z line in a sarcomere?

Accepted Answer

Actin

Question 4

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

Accepted Answer

They bind to troponin, causing a conformational change that exposes myosin-binding sites on actin.

Question 5

Which of the following best explains why curare poisoning leads to paralysis?

Accepted Answer

Curare blocks acetylcholine receptors at the neuromuscular junction, preventing muscle contraction.

Question 6

Which of the following is true regarding the 'sliding filament' theory of muscle contraction?

Accepted Answer

Actin and myosin filaments slide past each other, shortening the sarcomere without changing the length of the filaments.

Question 7

A patient is injected with botulinum toxin (Botox) in a facial muscle. Which of the following best describes the effect at the neuromuscular junction?

Accepted Answer

The toxin blocks the release of acetylcholine, preventing muscle contraction.

Question 8

Which of the following muscle fiber types is most resistant to fatigue and optimal for endurance activities such as marathon running?

Accepted Answer

Type I (slow oxidative) fibers

Question 9

Which of the following best describes the sequence of events leading to skeletal muscle contraction after an action potential reaches the neuromuscular junction?

Accepted Answer

Acetylcholine is released → T-tubules depolarize → Sarcoplasmic reticulum releases $\mathrm{Ca^{2+}}$ → Troponin binds $\mathrm{Ca^{2+}}$ → Myosin binds actin

Question 10

Which of the following best explains why muscles can only pull and not push?

Accepted Answer

Muscle contraction is due to the sliding of filaments, which shortens the muscle but cannot extend it actively.

Question 11

Which of the following is a direct effect of increasing the frequency of action potentials in a motor neuron innervating a muscle fiber?

Accepted Answer

Temporal summation, resulting in increased force of contraction in the same muscle fiber.

Question 12

Which of the following adaptations would you expect in the skeletal muscles of a professional long-distance swimmer compared to a non-athlete?

Accepted Answer

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

Question 13

Which of the following best describes the function of titin in the sarcomere?

Accepted Answer

Titin anchors myosin filaments and provides elasticity to the sarcomere.

Question 14

A person suffers from a genetic disorder that reduces the number of functional T-tubules in their skeletal muscle fibers. Which of the following symptoms would most likely result?

Accepted Answer

Slower and weaker muscle contractions due to impaired transmission of action potentials into the muscle fiber.

Question 15

Which of the following statements about the role of ATP in muscle contraction is correct?

Accepted Answer

ATP hydrolysis by myosin provides the energy for the power stroke and detachment of myosin from actin.

Question 16

Which of the following best explains why botulism from improperly canned food can be fatal?

Accepted Answer

The toxin blocks acetylcholine release, paralyzing the diaphragm and causing respiratory failure.

Question 17

Which of the following is a characteristic of smooth muscle cells?

Accepted Answer

They are spindle-shaped, have a single nucleus, and are not striated.

Question 18

Which of the following best describes the effect of aerobic exercise on skeletal muscle fibers?

Accepted Answer

It increases the density of capillaries, myoglobin content, and mitochondria, enhancing oxidative capacity.

Muscle Structure and Function in Vertebrates (Lecture 12)

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