Smooth muscle contraction

Question 1

What are the 2 biggest differences between smooth muscle and skeletal muscle contraction?

Answer 1

1. Calmodulin vs. Troponin

2. Calcium from pumps vs. sarcoplasmic reticulum

Question 2

What initiates smooth muscle contraction?

Answer 2

Calcium entering the cell and binding to calmodulin

Question 3

What is the function of the calcium-calmodulin complex?

Answer 3

To bind to/activate myosin light chain kinase (MLCK)

Question 4

What is MLCK and what does it do?

Answer 4

Myosin light chain kinase

phosphorylates a light chain within a myosin head, allowing it to bind actin

Question 5

What is the rate limiting factor in smooth muscle contraction?

Answer 5

calcium.

Question 6

T/F smooth muscle cell contraction is more rapid than skeletal muscle contraction.

Answer 6

False. the myosin-actin cross bridge is intact for longer in smooth muscle

Question 7

What does myosin phosphatase do?

Answer 7

de-phosphorylates the myosin light chain

Question 8

T/F Onset and relaxation of smooth muscle contraction is much slower that in skeletal muscle and cardiac muscle.

Answer 8

True

Question 9

Why is onset and relaxation of smooth muscle slow?

Answer 9

1. calcium channels open slowly, but stay open longer

2. calcium is removed from the cell at a slow rate (calcium pumps)

Question 10

How does smooth muscle produce prolonged muscle tone without excessive energy expenditure?

Answer 10

1. long cross-bridge cycle

2. slow contraction onset and relaxation

Question 11

In what ways are smooth muscle contractions regulated?

Answer 11

1. Nervous input (multi-unit esp.)
2. Hormonal input
3. Muscle cell stretch
4. Chemical environement (e.g. lack of O2, excess CO2, increased H+ concentrations…)