Physiology of Smooth Muscle - Karius

Question 1

Where is smooth muscle found?

Answer 1

Vasculature (esp arteries)
GI tract
Urogenital tract
Respiratory tract and eye

Question 2

How is smooth muscle different than skeletal muscle?

Answer 2

Thin filaments anchor to dense bodies, more actin
NO troponin
2x as much actin
1/4 amount of myosin
Contains kinase and phosphatase

Question 3

When there is a lot of gap junctions in smooth muscle, what is the result?

Answer 3

Contraction is coordinated

ex. gut

Question 4

Where is smooth muscle more autonomous?

Answer 4

Vasculature

-vs gut that is coordinated by CNS

Question 5

How is the gut innervated?

Answer 5

Intrinsic - sensory and motor neurons , independent of CNS
-ex. gut and trachea
Extrinsic - ANS - allows CNS to control viscera

Question 6

What are the 3 major NT of gut and effects?

Answer 6

ACh - excite smooth muscle in gut
NE or Epi - contraction of vascular smooth m and inhibits gut smooth muscle
NO - major inhibitory on smooth muscle
-acts via cGMP mechanism

Question 7

What type of receptors does smooth muscle have?

Answer 7

Muscarinic cholinergic
Adrenergic (alpha and beta)
(FYI - varicosities)
VS skeletal ACh receptors only

Question 8

2 hormones that can elicit smooth muscle contraction?

Answer 8

Epinephrine

Cholecystokinin

Question 9

What do endothelial cells secrete?

Answer 9

EDRF - endothelium-derived relaxing factor)

-now known to be NO

Question 10

Where does Ca++ come from in smooth muscle?

Answer 10

Extracellular sources - open with binding of ligand

Sarcoplasmic reticulum - open with depolarization

Question 11

Can smooth muscle be activated in the absence of an action potential?

Answer 11

Yes

Because PKC is activated (I think, maybe…)

Question 12

To have sustained contraction of smooth muscle what is required?

Answer 12

Ca++ from extracellular sources

Question 13

What is the first step of muscle contraction?

Answer 13

Increase in intracellular calcium

-from SR or extracellular

Question 14

Step 2 of muscle contraction?

Answer 14

Calcium binds with Calmodulin

Question 15

Step 3 of muscle contraction?

Answer 15

Calmodulin activated MLCK

Question 16

Step 4 of muscle contraction?

Answer 16

MLCK phosphorylates light chain

-smooth m. uses 2 ATP for each cross bridge cycle

Question 17

Step 5 of muscle contraction?

Answer 17

Myosin cross bridge can begin cycle

-2 distinct inorganic phosphates involved - one on light chain, other at myosin head

Question 18

Smooth muscle relaxation

Answer 18

With the inactivation of MLCK, a phosphatase is activated. This phosphatase will remove the Pi from the myosin light chain and allow relaxation

Question 19

The importance of latch mechanism?

Answer 19

Decreases energy utilization by smooth muscle

Makes up for additional ATP used to phosphorylate the light chain in each cycle of smooth muscle contraction

Question 20

Passive tension in smooth muscle

Answer 20

Comes form stretching the membranes (think rubber band)
With every stretch of muscle cell, passive tension increase a little, but as actin and myosin rearrange, the passive tension decreases

Question 21

Actin-myosin in smooth muscle

Answer 21

Not organized, more random
Once myosin heads are free, will interact with a DIFFERENT thin filament
This 1. reduces passive tension by reducing strain
2. allows smooth m. to generate active tension over a wide range of length
Difference from skeletal - does not develop sustained passive tension

Question 22

One of the most interesting things about smooth muscle according to Karius

Answer 22

It is plastic - can change from one cell type to another and back
Common in vasculature - damage signals cells to become fibroblasts that can secrete collagen to repair the damage