Smooth Muscle Physiology

Question 1

What is the nerve-to-cell relationship in a multi-unit smooth muscle?

Answer 1

• each cell is innervated by a single nerve, so that fibers operate individually
  ex: ciliary muscle, iris, piloerector muscles

Question 2

What is the nerve-to-cell relationship in a unitary smooth muscle?

Answer 2

NOT every cell has its own innervation

-gap junctions allow coordination

Question 3

What structures does actin attach to in smooth muscle?

Answer 3

-dense bodies

Question 4

True or False: dense bodies can rearrange smooth muscle fibers to change the directionality of ctx.

Answer 4

True

Question 5

True or False: the time that myosin and actin are attached is of longer duration in smooth muscle than in skeletal muscle

Answer 5

True

Question 6

Delineate the mechanism of smooth muscle ctx.

Answer 6

1) Ca2+ enters cell through sarcolemma or from the sarcoplasmic reticulum
2) calcium-calmodulin complex forms and activates myosin light chain kinase to propel myosin head
3) MLC phosphatase deactivates myosin = relaxation

Question 7

Where does a smooth muscle cell obtain most of its calcium supply?

Answer 7

from extracellular space

Question 8

What channels and receptors are at work when calcium is released from the sarcoplasmic reticulum in smooth muscle?

Answer 8

• • IP3-gated channels

- - ryanodine receptors

Question 9

What structure on a nerve is responsible for stimulating smooth muscle?

Answer 9

varicosities (NTR release sites)

–varicosities act in a similar manner to motor neurons

Question 10

What sympathetic NTR’s are used in smooth muscle innervation?

Answer 10

norepinephrine and epinephrine

–can be excitatory or inhibitory depending on the organ

Question 11

What are the excitatory effects of epinephrine or norepi on smooth muscle and what is an example of a receptor that would be used?

Answer 11

smooth muscle ctx

alpha-1 adrenergic receptor

Question 12

What are the inhibitory effects of epinephrine or norepi on smooth muscle and what is an example of a receptor that would be used?

Answer 12

smooth muscle relaxation

beta-2 adrenergic receptor

Question 13

What NTR is used in parasympathetic smooth muscle innervation and with what type of receptors?

Answer 13

Ach

cholinergic receptors

Question 14

What is the action of angiotensin II, vasopressin, and endothelin?

Answer 14

smooth muscle ctx

Question 15

What is the action of adenosine or nitric oxide?

Answer 15

smooth muscle relaxation

Question 16

What are examples of environmental cues for control of smooth muscle?

Answer 16

• hypoxia
• increased carbon dioxide
• prostaglandins
• atrial natriuretic peptide

Question 17

What effect does hypoxia, increased carbon dioxide, prostaglandins, and atrial natriuretic peptide have on smooth muslces?

Answer 17

relaxation

Question 18

When is ATP utilized in the ctx of smooth muscle?

Answer 18

• ATP is used to phosphorylate the myosin head

- ATP is used by myosin ATPase to detach the myosin head from actin

Question 19

What is the importance of the latch mechanism in smooth muscle ctx?

Answer 19

it allows ctx to be maintained even while calcium levels in the cell are declining d/t removal by the calcium pumps

Question 20

What is unique about smooth muscle stretching versus skeletal muscle stretching?

Answer 20

-as smooth muscle is stretched, the dense bodies can rearrange it to allow for more stretch, while maintaining contractile ability; smooth muscle can thus shift its optimal range