Q: Which equation best represents the relationship between calcium, calmodulin, and MLCK activation in smooth muscle contraction?

$$Ca^{2+}$$ + \text{calmodulin} \rightarrow \text{Ca}^{2+}\text{-calmodulin complex} \rightarrow \text{activates MLCK}$$

Question 1

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

Accepted Answer

Smooth muscle lacks t-tubules and relies on caveolae for calcium entry, resulting in slower contraction and relaxation.

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 is TRUE regarding the regulation of smooth muscle contraction?

Accepted Answer

Myosin light chain kinase (MLCK) phosphorylates myosin light chains, increasing myosin ATPase activity.

Question 4

Which equation best represents the relationship between calcium, calmodulin, and MLCK activation in smooth muscle contraction?

Accepted Answer

$$Ca^{2+}$$ + 	ext{calmodulin} ightarrow 	ext{Ca}^{2+}	ext{-calmodulin complex} ightarrow 	ext{activates MLCK}$$

Question 5

A drug that increases myosin light chain phosphatase (MLCP) activity in smooth muscle would most likely have which effect?

Accepted Answer

Decrease calcium sensitivity and promote relaxation

Question 6

Which of the following best distinguishes single-unit smooth muscle from multiunit smooth muscle?

Accepted Answer

Single-unit smooth muscle cells are electrically coupled via gap junctions and contract as a coordinated unit.

Question 7

Which of the following is a characteristic of smooth muscle but NOT of skeletal muscle?

Accepted Answer

Ability to maintain contraction in a latch state with low ATP consumption

Question 8

A researcher observes that a smooth muscle cell contracts in response to stretch, even in the absence of neural input. Which mechanism is most likely responsible?

Accepted Answer

Opening of stretch-activated calcium channels leading to myogenic contraction

Question 9

Which of the following best describes the role of caveolae in smooth muscle cells?

Accepted Answer

They are invaginations of the plasma membrane that facilitate calcium entry from the extracellular fluid.

Question 10

Which of the following statements about cardiac muscle is correct?

Accepted Answer

Cardiac muscle cells are connected by gap junctions in intercalated disks, allowing electrical coupling.

Question 11

A patient with a mutation that prevents the formation of dense bodies in smooth muscle would most likely experience which of the following?

Accepted Answer

Impaired transmission of force from actin filaments, leading to weak contractions

Question 12

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

Accepted Answer

It is a state where myosin remains attached to actin after dephosphorylation, maintaining tension with minimal ATP consumption.

Question 13

Which of the following is a key difference between cardiac and smooth muscle?

Accepted Answer

Cardiac muscle contains sarcomeres, while smooth muscle does not.

Question 14

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

Accepted Answer

Contraction initiated by chemical signals without a change in membrane potential

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 → Increased myosin ATPase activity

Question 16

A smooth muscle cell is exposed to a drug that blocks voltage-gated calcium channels. Which of the following would most likely occur?

Accepted Answer

Decreased contraction due to reduced calcium entry

Question 17

Which of the following best describes the function of intermediate filaments in smooth muscle?

Accepted Answer

They anchor actin filaments to dense bodies, helping transmit contractile force throughout the cell.

Question 18

Which of the following is a feature shared by both cardiac and smooth muscle, but not skeletal muscle?

Accepted Answer

Ability to contract without neural stimulation (autorhythmicity)

Question 19

A smooth muscle cell is exposed to a chemical that increases the activity of myosin light chain kinase (MLCK). What is the most likely effect on muscle contraction?

Accepted Answer

Increased phosphorylation of myosin light chains and enhanced contraction

Question 20

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

Accepted Answer

Smooth muscle enters a latch state, where dephosphorylated myosin remains attached to actin.

Smooth and Cardiac Muscle: Structure, Function, and Physiology

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드