Smooth Muscle Physiology

Question 1

With Multi-unit smooth muscle:
The fibers operate in what manner?
They are innervated by?
Examples?

Answer 1

1) Individually
2) Single nerve
3) Ciliary muscles of eye, iris, piloerector muscles

Question 2

With Unitary smooth muscle:
They are also known as?
They operate in what manner?
Cell membranes adhere and contain?
Examples?

Answer 2

1) Visceral smooth muscle
2) Work together as a unit
3) Gap junctions
4) GI tract, bile ducts, uterus

Question 3

How is cycling of myosin cross bridges in smooth muscle compare to skeletal?
How is the time myosin and actin are attached in smooth muscle compare to skeletal?

Answer 3

1) Slower in smooth m.

2) Greater in smooth m.

Question 4

What is the key molecule in the activation of a smooth muscle contraction?
What is the key enzyme?

Answer 4

1) Calcium

2) Calmodulin

Question 5

The calmodulin-calcium complex activates what enzyme in the activation of smooth muscle contraction?

Answer 5

Myosin light chain kinase

Question 6

What enzyme is a major player in the relaxation stage of smooth muscle contraction?

Answer 6

Myosin light chain phosphatase

Question 7

In the nerve stimulation of smooth muscle, what serve as neurotransmitter release sites?

Answer 7

Varicosities

Question 8

Angiotensin II, vasopressin, and endothelin have what type of effect on smooth muscle?
Adenosine has what type of effect on smooth muscle?
Nitric oxide has what type of effect on smooth muscle?

Answer 8

1) Contraction
2) Relaxation
3) Relaxation

Question 9

Hypoxia, excess CO2, increased H+, Adenosine, and increased K+ have what type of effect on smooth muscle?

Answer 9

Relaxation

Question 10

APs such as plateaus and spike potentials only occur in what type of smooth muscle?

Answer 10

Unitary smooth muscle

Question 11

What is the latch mechanism?

Answer 11

Myosin and actin remaining connected to increase time of contraction and tension while decreasing ATP usage

Question 12

In the latch mechanism,
What happens to light chains?
At what rate is the cycle occuring?
What is still generating tension?

Answer 12

1) Dephosphorylation of light chains
2) Slowly
3) Attached cross bridges

Question 13

Norepinephrine binding to alpha 1 adrenergic receptors has what type of effect on smooth muscle?

Answer 13

Contraction

Question 14

The movement of a bolus of food through the small intestine has what type of effect on smooth muscle?

Answer 14

Contraction

Question 15

What allows the smooth muscle in your stomach to still contract even when it is stretched from a large meal?

Answer 15

Myosin is able to interact with different actin filaments due to actin and myosin rearrangement

Question 16

What is the actin and myosin composition in smooth muscle vs skeletal muscle?

Answer 16

More actin is smooth but more myosin in skeletal

Question 17

Most of the calcium for contraction of a smooth muscle cell comes from?

Answer 17

Extracellular stores

Question 18

What are the three methods for getting calcium out of a smooth muscle cell?

Answer 18

1) SERCA
2) 3Na/Ca2+ antiporter
3) Sarcolemmal Ca2+ ATPase

Question 19

What is different about the length tension curve between skeletal and smooth muscle?

Answer 19

Smooth muscle can adjust its length tension curve in order to maintain closer to the ideal