Question 1

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

Accepted Answer

Smooth muscle relies on phosphorylation of myosin light chains and has slower calcium handling mechanisms.

Question 2

A patient is experiencing difficulty with peristalsis in the gastrointestinal tract. Which type of smooth muscle is most likely affected?

Accepted Answer

Single-unit (unitary or visceral) smooth muscle

Question 3

Which of the following statements about smooth muscle is correct?

Accepted Answer

Smooth muscle contraction is initiated by calcium binding to calmodulin, not troponin.

Question 4

During smooth muscle contraction, which enzyme is directly responsible for phosphorylating the myosin light chain?

Accepted Answer

Myosin light chain kinase (MLCK)

Question 5

Which of the following best describes the 'latch state' in smooth muscle?

Accepted Answer

A state where myosin remains attached to actin after dephosphorylation, maintaining tension with low ATP consumption.

Question 6

Which of the following is a key difference between single-unit and multiunit smooth muscle?

Accepted Answer

Single-unit smooth muscle cells are connected by gap junctions, allowing coordinated contraction, while multiunit smooth muscle cells are not.

Question 7

A researcher applies a drug that increases the activity of myosin light chain phosphatase (MLCP) in smooth muscle. What is the most likely effect on muscle contraction?

Accepted Answer

Decreased contraction due to increased dephosphorylation of myosin light chains.

Question 8

Which of the following best describes the source(s) of calcium that initiate smooth muscle contraction?

Accepted Answer

From both the sarcoplasmic reticulum (SR) and extracellular fluid (ECF)

Question 9

A patient has a mutation that prevents the formation of caveolae in smooth muscle cells. Which process would be most directly affected?

Accepted Answer

Calcium entry from the extracellular fluid

Question 10

Which of the following is true regarding the regulation of smooth muscle contraction by membrane potential changes?

Accepted Answer

Smooth muscle contraction can be triggered by both electrical (electromechanical coupling) and chemical (pharmacomechanical coupling) signals.

Question 11

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

Accepted Answer

Smooth muscle has a latch state where myosin remains attached to actin even after dephosphorylation.

Question 12

Which of the following is a characteristic unique to cardiac muscle compared to both skeletal and smooth muscle?

Accepted Answer

Intercalated disks with gap junctions

Question 13

A drug that blocks voltage-gated calcium channels in smooth muscle would most likely have which effect?

Accepted Answer

Decrease smooth muscle contraction by reducing calcium influx

Question 14

Which of the following best describes the role of calmodulin in smooth muscle contraction?

Accepted Answer

Calmodulin binds to calcium and activates myosin light chain kinase (MLCK).

Question 15

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

Accepted Answer

Calcium binds to calmodulin → MLCK activation → Myosin light chain phosphorylation → Contraction

Question 16

Which of the following is a feature of multiunit smooth muscle?

Accepted Answer

Each cell is innervated and contracts independently.

Question 17

A patient with hypertension is given a drug that increases the activity of MLCP in vascular smooth muscle. What is the expected physiological effect?

Accepted Answer

Decreased vascular resistance due to enhanced relaxation

Question 18

Which of the following best explains why cardiac muscle can generate its own action potentials?

Accepted Answer

Cardiac muscle cells have pacemaker potentials due to unstable membrane potentials.

Question 19

Which of the following is a correct comparison between skeletal, cardiac, and smooth muscle?

Accepted Answer

Only skeletal and cardiac muscle are striated due to sarcomere structure.

Question 20

A smooth muscle cell is exposed to a chemical that increases the activity of store-operated Ca$$^{2+}$$ channels. What is the most likely result?

Accepted Answer

Increased cytosolic Ca$$^{2+}$$ and enhanced contraction

Smooth and Cardiac Muscle: Structure, Function, and Physiology

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