$$\text{Myosin} + \text{ATP} \xrightarrow{\text{Myosin Light Chain Kinase}} \text{Myosin-P} + \text{ADP}$$

Question 1

Which structural feature is unique to smooth muscle cells compared to skeletal muscle cells?

Accepted Answer

Spindle-shaped fibers with a central nucleus

Question 2

What is the primary function of caveolae in smooth muscle cells?

Accepted Answer

Trap extracellular calcium for contraction

Question 3

Which of the following best describes the arrangement of smooth muscle in the walls of hollow organs such as the intestine?

Accepted Answer

Longitudinal and circular layers of smooth muscle run at right angles to each other

Question 4

Which of the following is TRUE regarding the contraction mechanism in smooth muscle?

Accepted Answer

Calcium binds to calmodulin, activating myosin light chain kinase

Question 5

A patient is experiencing prolonged smooth muscle contractions in the gastrointestinal tract. Which of the following best explains this phenomenon?

Accepted Answer

Delayed removal of cytosolic calcium due to slower calcium pumps

Question 6

Which equation best represents the activation of myosin ATPase in smooth muscle contraction?

Accepted Answer

$$	ext{Myosin} + 	ext{ATP} \xrightarrow{	ext{Myosin Light Chain Kinase}} 	ext{Myosin-P} + 	ext{ADP}$$

Question 7

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

Accepted Answer

Multi-unit smooth muscle cells contract independently due to fewer gap junctions

Question 8

Which of the following mechanisms is NOT involved in the relaxation of smooth muscle?

Accepted Answer

Activation of myosin light chain kinase

Question 9

A researcher applies a hormone to a smooth muscle cell, resulting in contraction. Which pathway is most likely involved?

Accepted Answer

Hormone binds to G-protein linked receptor, triggering Ca$$^{2+}$$ release from the SR

Question 10

Which of the following is a plausible consequence of a genetic mutation that prevents the formation of caveolae in smooth muscle cells?

Accepted Answer

Reduced ability to trap extracellular calcium, leading to impaired contraction

Question 11

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

Accepted Answer

Calcium influx and efflux are slower due to reliance on extracellular sources and caveolae

Question 12

Which of the following is NOT a source of calcium for smooth muscle contraction?

Accepted Answer

T-tubules

Question 13

A smooth muscle cell is exposed to a neurotransmitter that causes depolarization. Which event is most likely to occur next?

Accepted Answer

Opening of voltage-gated Ca$$^{2+}$$ channels and influx of Ca$$^{2+}$$

Question 14

Which of the following best describes the role of myosin phosphatase in smooth muscle relaxation?

Accepted Answer

Removes phosphate from myosin, decreasing myosin ATPase activity

Question 15

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

Accepted Answer

Ca$$^{2+}$$ influx → Ca$$^{2+}$$ binds calmodulin → Myosin light chain kinase activation → Myosin phosphorylation → Cross bridge formation

Question 16

Which of the following factors can stimulate smooth muscle contraction?

Accepted Answer

Hormones, chemicals, physical factors, and autorhythmic activity

Question 17

Which of the following is a plausible effect of blocking Ca$$^{2+}-Na$^+$$ antiport exchange in smooth muscle cells?

Accepted Answer

Impaired removal of cytosolic Ca$$^{2+}$$, leading to sustained contraction

Question 18

Which of the following is TRUE regarding the myofilaments in smooth muscle?

Accepted Answer

They lack a troponin-tropomyosin complex and are always ready for cross bridge formation

Question 19

A patient with a mutation in calmodulin is likely to experience which of the following symptoms?

Accepted Answer

Reduced smooth muscle contraction due to inability to activate myosin light chain kinase

Smooth Muscle Tissue: Anatomy and Contraction Mechanisms

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