Q: Which equation best represents the relationship between calcium influx and contraction in smooth muscle?

$$[Ca$$^{2+}$$]_{cytosol} \uparrow \Rightarrow \text{Contraction}$$

Question 1

Which of the following best describes the arrangement of smooth muscle layers in most hollow organs?

Accepted Answer

Two layers: one longitudinal and one circular, with fibers oriented perpendicularly

Question 2

What is the primary function of varicosities in smooth muscle innervation?

Accepted Answer

To store and release neurotransmitters into a wide synaptic cleft called a diffuse junction

Question 3

Which of the following is TRUE regarding the excitation-contraction coupling in smooth muscle?

Accepted Answer

Calcium binds to calmodulin, which activates myosin light chain kinase

Question 4

A patient is experiencing bronchoconstriction due to smooth muscle contraction in the airways. Which neurotransmitter would most likely inhibit this contraction?

Accepted Answer

Norepinephrine

Question 5

Which of the following features distinguishes unitary (visceral) smooth muscle from multiunit smooth muscle?

Accepted Answer

Presence of gap junctions allowing coordinated contraction as a syncytium

Question 6

Smooth muscle contraction is slower and more sustained than skeletal muscle contraction. Which of the following mechanisms contributes to this property?

Accepted Answer

Longer duration of crossbridge attachment and slower Ca$$^{2+}$$ removal

Question 7

Which equation best represents the relationship between calcium influx and contraction in smooth muscle?

Accepted Answer

$$[Ca$$^{2+}$$]_{cytosol} \uparrow \Rightarrow 	ext{Contraction}$$

Question 8

Which of the following is NOT a property of smooth muscle fibers compared to skeletal muscle fibers?

Accepted Answer

Smooth muscle fibers are under voluntary control

Question 9

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

Accepted Answer

Myosin light chain kinase (MLCK)

Question 10

A bladder is able to stretch and temporarily store urine without a rapid increase in wall tension. Which physiological response explains this property?

Accepted Answer

Stress-relaxation response

Question 11

Which of the following statements about calcium regulation in smooth muscle is correct?

Accepted Answer

Calcium-induced calcium release (CICR) occurs via caveolae and SR

Question 12

Which of the following best describes the role of intermediate filaments and dense bodies in smooth muscle?

Accepted Answer

They transmit tension to the sarcolemma and anchor thin filaments

Question 13

Which of the following is a correct sequence for excitation-contraction coupling in smooth muscle?

Accepted Answer

Ca$$^{2+}$$ enters cytosol $$\rightarrow$$ binds calmodulin $$\rightarrow$$ activates MLCK $$\rightarrow$$ myosin phosphorylation $$\rightarrow$$ crossbridge formation

Question 14

Which of the following is a property unique to multiunit smooth muscle?

Accepted Answer

Independent fibers form motor units and allow recruitment

Question 15

Which of the following chemical stimuli can enhance smooth muscle contraction by increasing Ca$$^{2+}$$ entry into the cytoplasm?

Accepted Answer

High CO$$_2$$, low pH, low O$$_2$$

Question 16

Which of the following best explains why smooth muscle can maintain tone for prolonged periods without fatigue?

Accepted Answer

ATP synthesis primarily by aerobic respiration and slower crossbridge cycling

Question 17

Which of the following is a correct comparison between skeletal and smooth muscle regarding connective tissue coverings?

Accepted Answer

Skeletal muscle has epimysium, perimysium, and endomysium; smooth muscle has only endomysium

Question 18

Which of the following is TRUE regarding the arrangement of thick and thin filaments in smooth muscle?

Accepted Answer

Thick filaments are fewer and myosin heads are distributed along the entire length

Question 19

Which of the following best describes the mechanism by which smooth muscle fibers contract?

Accepted Answer

Fibers contract in a corkscrew manner, shortening along their length

Lecture 8 Smooth Muscle: Structure, Function, and Comparison with Skeletal Muscle

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