9- Contraction Of Smooth Muscle

Question 0

Calmodulin

Answer 0

Binding by troponin, calcium ions trigger myosin activity In all striated muscle types, but in smooth muscle, they activate myosin by interacting with a regulatory molecule called calmodulin, cytoplasmic calcium binding protein.

Question 1

Sequence of events in excitation contraction coupling of smooth muscle.

Answer 1

Pg 311

1. Calcium ions enter cytosol from the ECF or from the scant SR.
2. Calcium binds to and activates calmodulin.
3. Activated calmodulin activates the myosin light chain kinase enzymes.
4. Activated kinase enzyme catalyzes transfer of phosphate to myosin heads, activating the myosin head ATPases.
5. Phosphorylated myosin heads from cross bridges with actin of the thin filaments and shortening occurs.
6. Cross bridge activity ends when phosphate is removed from the myosin heads by phosphorylase enzymes and intracellular calcium levels fall.

Question 2

Myosin kinase or myosin light chain kinase

Answer 2

Calmodulin interacts with this kinase enzyme which phosphorylates the myosin heads.

Pg 312

Question 3

Stress relaxation response

Answer 3

Allows a hollow organ to fill or expand slowly to accommodate a greater volume without promoting strong contractions that would expel its contents.

Question 4

Single unit smooth muscle or visceral muscle

Answer 4

In the walls of hollow organs except heart. It’s cells:

1. Contract rhythmically and as a unit.
2. Are electrically coupled to one another by gap junctions.
3. Often exhibit spontaneous action potential.

Question 5

Multiunit smooth muscle

Answer 5

Large airways to the lungs, and large arteries. Arrector pipili muscles, and internal eye muscles.

Pg 316

Question 6

Myosblasts

Answer 6

All muscles tissues developed from this embryonic mesoderm cell.

Read about on pg 316 and 317