Question 1

Which of the following best describes the arrangement of thick and thin filaments in smooth muscle compared to skeletal muscle?

Accepted Answer

Smooth muscle filaments are arranged in a diamond-shaped lattice, allowing contraction in multiple directions.

Question 2

Which of the following is a key difference in the mechanism of contraction between smooth muscle and skeletal muscle?

Accepted Answer

Smooth muscle contraction is initiated by phosphorylation of myosin light chains, while skeletal muscle contraction is initiated by troponin binding to Ca$$^{2+}.$$

Question 3

A patient presents with difficulty regulating blood flow in their large arteries. Which type of smooth muscle is most likely affected?

Accepted Answer

Multi-unit smooth muscle

Question 4

Which of the following best explains why smooth muscle can maintain contraction for long periods with minimal energy expenditure?

Accepted Answer

The latch phenomenon allows crossbridges to remain attached for extended periods without continuous ATP hydrolysis.

Question 5

Which of the following is TRUE regarding the excitation of single-unit smooth muscle?

Accepted Answer

It can generate spontaneous depolarizations due to pacemaker or slow wave potentials.

Question 6

During smooth muscle contraction, which protein does Ca$$^{2+}$$ bind to in order to initiate the contractile process?

Accepted Answer

Calmodulin

Question 7

Which of the following best describes the function of gap junctions in single-unit smooth muscle?

Accepted Answer

They allow rapid spread of depolarization from cell to cell, enabling coordinated contraction.

Question 8

A sudden stretch of the urinary bladder wall leads to a brief contraction followed by relaxation. What is this response called?

Accepted Answer

Stress-relaxation response

Question 9

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

Accepted Answer

It maintains continuous tension and is commonly found in blood vessels.

Question 10

Which of the following best explains why smooth muscle contraction is slower than skeletal muscle contraction?

Accepted Answer

Smooth muscle has lower ATPase activity and lacks troponin, resulting in slower crossbridge cycling.

Question 11

Which of the following is NOT a way that smooth muscle can be excited?

Accepted Answer

Direct stimulation by somatic motor neurons

Question 12

Which of the following statements about multi-unit smooth muscle is correct?

Accepted Answer

Each unit must be individually stimulated by autonomic neurons for contraction.

Question 13

Which of the following best describes the role of myosin light chain kinase (MLCK) in smooth muscle contraction?

Accepted Answer

MLCK phosphorylates myosin, enabling it to bind to actin and initiate contraction.

Question 14

Which of the following is a distinguishing feature of cardiac muscle compared to skeletal and smooth muscle?

Accepted Answer

Presence of intercalated discs for rapid electrical transmission

Question 15

A drug that blocks voltage-gated Ca$$^{2+}$$ channels in smooth muscle would most likely have which of the following effects?

Accepted Answer

It would inhibit contraction by preventing Ca$$^{2+}$$ influx and subsequent activation of calmodulin.

Question 16

Which of the following best explains why the strength of single-unit smooth muscle contraction depends on the number of crossbridges formed rather than the number of motor units recruited?

Accepted Answer

Single-unit smooth muscle cells are electrically coupled via gap junctions, so they contract as a unit.

Question 17

Which of the following is a correct sequence of events in smooth muscle contraction?

Accepted Answer

Ca$$^{2+}$$ influx → Ca$$^{2+}-$$calmodulin complex formation → MLCK activation → Myosin phosphorylation → Crossbridge formation

Question 18

Which of the following is a real-life example of phasic smooth muscle activity?

Accepted Answer

Peristaltic contractions in the digestive tract

Question 19

Which of the following statements about the source of Ca$$^{2+}$$ for contraction is correct?

Accepted Answer

Smooth muscle relies primarily on extracellular Ca$$^{2+}$$ influx, while skeletal muscle relies on Ca$$^{2+}$$ release from the sarcoplasmic reticulum.

Smooth Muscle: Structure, Function, and Comparison with Other Muscle Types

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