Physiology of smooth muscle

Question 1

What is different about the sarcoplasmic reticulum in smooth muscle when compared to that in skeletal muscle?

Answer 1

it is much less developed

Question 2

How does smooth muscle get its calcium?

Answer 2

Through both the SR and ECF

Question 3

Release of calcium from the SR utilizes what?

Answer 3

A Gq protein

Question 4

When Gq proteins are activated what is produced?

Answer 4

IP3/DAG

Question 5

What is the role of IP3/DAG?

Answer 5

it is a very strong stimulus of calcium to be released from the SR

Question 6

How does smooth muscle get its Ca2+ from the ECF?

Answer 6

via calcium channels

Question 7

Why does smooth muscle require Ca2+ from extracellular sources?

Answer 7

because smooth muscle has sustained contractions

Question 8

At rest, what does the myosin head have associated with it?

Answer 8

ADP and Pi

Question 9

What is different about the actin in smooth muscle when compared to the actin in skeletal muscle?

Answer 9

actin in smooth muscle does not have tropomyosin bound to it

Question 10

What does a rise in intracellular Ca2+ cause?

Answer 10

it causes 4 calcium molecules to bind to 1 calmodulin molecule

Question 11

What happens when calcium binds to calmodulin?

Answer 11

the calmodulin will activate myosin light chain kinase

Question 12

what is the action of kinases?

Answer 12

kinases will add an inorganic phosphate to something

Question 13

When the MLCK is activated what happens?

Answer 13

It adds an inorganic phosphate to the myosin light chain

Question 14

What happens once the MLC is phosphorylated?

Answer 14

the myosin head has a higher affinity for the active site on the actin

Question 15

How many inorganic phosphates will be associated with the myosin found in smooth muscle?

Answer 15

2

Question 16

What happens when calcium leaves calmodulin and the MLCK is no longer activated?

Answer 16

a myosin light chain phosphorylase will remove the inorganic phosphate from the myosin light chain, and myosin will once again have a low affinity for the actin binding sites

Question 17

What are two reasons why smooth muscle overall uses less ATP than skeletal muscle?

Answer 17

1) the isoform of the myosin that is found in smooth muscle is much slower than that found in skeletal muscle= less cycles per minute
2) the latch mechanism

Question 18

What does the latch mechanism state?

Answer 18

at any given moment in time, the inorganic phosphate that is on the myosin light chain can be removed

Question 19

if the inorganic phosphate is removed from the myosin light chain, what will happen?

Answer 19

The cross-bridge cycle will continue through the power stroke

Question 20

What happens at the end of the power stroke, if the Pi has been removed from the myosin light chain?

Answer 20

the mysoin and actin will now have a low affinity for the ATP that is trying to bind. So it will take a long time for it to finally bind, which will then cause the myosin and actin to dissociate

Question 21

Swellings in axon that function as the presynaptic terminal. Neurotransmitter is released from here

Answer 21

varicosity

Question 22

What is nitric oxide made by?

Answer 22

endothelial cells

Question 23

What is NO released into?

Answer 23

the space inbetween the endothelial cells and the smooth muscle

Question 24

What is the role of NO?

Answer 24

it relaxes smooth muscle

Question 25

What’s an example of mechanical influence?

Answer 25

stretch