$\text{Protein} + \text{ATP} \rightarrow \text{Protein-PO}_4 + \text{ADP}$

Question 1

Which of the following is a key anatomical difference between smooth muscle and skeletal muscle cells?

Accepted Answer

Smooth muscle cells are fusiform, smaller, and have a single, centrally located nucleus.

Question 2

During smooth muscle contraction, which protein does calcium bind to in order to initiate the contraction process?

Accepted Answer

Calmodulin

Question 3

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

Accepted Answer

MLCK phosphorylates myosin light chains, enabling myosin to bind actin and generate contraction.

Question 4

Which of the following mechanisms is primarily responsible for smooth muscle relaxation?

Accepted Answer

Dephosphorylation of myosin light chains by myosin light chain phosphatase (MLCP)

Question 5

A patient is experiencing abnormal gut motility due to a defect in smooth muscle contraction. Which of the following steps is MOST likely impaired?

Accepted Answer

Phosphorylation of myosin light chains by MLCK

Question 6

Which equation correctly represents the phosphorylation reaction catalyzed by a kinase in smooth muscle?

Accepted Answer

$	ext{Protein} + 	ext{ATP} ightarrow 	ext{Protein-PO}_4 + 	ext{ADP}$

Question 7

Which of the following is TRUE regarding the arrangement of contractile proteins in smooth muscle?

Accepted Answer

Actin filaments are attached to dense bodies instead of Z-lines.

Question 8

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

Accepted Answer

Smooth muscle myosin heavy chain ATPase activity is slower, and contraction requires additional steps such as phosphorylation.

Question 9

Which of the following is a physiological property unique to smooth muscle compared to skeletal and cardiac muscle?

Accepted Answer

Contraction requires phosphorylation of myosin light chains.

Question 10

A researcher is studying the effects of a drug that inhibits MLCP (myosin light chain phosphatase) in smooth muscle. What is the most likely outcome?

Accepted Answer

Smooth muscle contraction will be prolonged due to sustained phosphorylation of myosin light chains.

Question 11

Which of the following best describes pharmacomechanical coupling in smooth muscle?

Accepted Answer

Contraction can be modulated by chemical signals without changes in membrane potential.

Question 12

Which of the following is NOT a location where smooth muscle is typically found?

Accepted Answer

Skeletal muscles attached to bones

Question 13

Which of the following statements about excitation-contraction coupling in smooth muscle is correct?

Accepted Answer

Calcium binds calmodulin, which activates MLCK to phosphorylate myosin light chains.

Question 14

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

Accepted Answer

Smooth muscle can be controlled by hormones, autonomic nervous system, and pacemaker potentials.

Question 15

Which of the following best describes the function of dense bodies in smooth muscle?

Accepted Answer

They serve as attachment points for actin filaments, analogous to Z-lines in skeletal muscle.

Question 16

A smooth muscle cell is exposed to a drug that blocks L-type voltage-gated calcium channels. What is the most likely effect?

Accepted Answer

Decreased contraction due to reduced calcium entry and less activation of calmodulin.

Question 17

Which of the following is TRUE regarding the relaxation of smooth muscle?

Accepted Answer

Relaxation is promoted by the activity of myosin light chain phosphatase (MLCP).

Question 18

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

Accepted Answer

Smooth muscle uses the latch state, where myosin remains attached to actin even after dephosphorylation.

Question 19

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

Accepted Answer

Calcium binds calmodulin → MLCK activation → Myosin light chain phosphorylation → Cross-bridge formation

Smooth Muscle: Anatomy, Physiology, and Comparison with Skeletal and Cardiac Muscle

Study Guide - Practice Questions