Flashcards in Physiology of Smooth Muscle - Karius Deck (22)
Where is smooth muscle found?
Vasculature (esp arteries)
Respiratory tract and eye
How is smooth muscle different than skeletal muscle?
Thin filaments anchor to dense bodies, more actin
2x as much actin
1/4 amount of myosin
Contains kinase and phosphatase
When there is a lot of gap junctions in smooth muscle, what is the result?
Contraction is coordinated
Where is smooth muscle more autonomous?
-vs gut that is coordinated by CNS
How is the gut innervated?
Intrinsic - sensory and motor neurons , independent of CNS
-ex. gut and trachea
Extrinsic - ANS - allows CNS to control viscera
What are the 3 major NT of gut and effects?
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
What type of receptors does smooth muscle have?
Adrenergic (alpha and beta)
(FYI - varicosities)
VS skeletal ACh receptors only
2 hormones that can elicit smooth muscle contraction?
What do endothelial cells secrete?
EDRF - endothelium-derived relaxing factor)
-now known to be NO
Where does Ca++ come from in smooth muscle?
Extracellular sources - open with binding of ligand
Sarcoplasmic reticulum - open with depolarization
Can smooth muscle be activated in the absence of an action potential?
Because PKC is activated (I think, maybe...)
To have sustained contraction of smooth muscle what is required?
Ca++ from extracellular sources
What is the first step of muscle contraction?
Increase in intracellular calcium
-from SR or extracellular
Step 2 of muscle contraction?
Calcium binds with Calmodulin
Step 3 of muscle contraction?
Calmodulin activated MLCK
Step 4 of muscle contraction?
MLCK phosphorylates light chain
-smooth m. uses 2 ATP for each cross bridge cycle
Step 5 of muscle contraction?
Myosin cross bridge can begin cycle
-2 distinct inorganic phosphates involved - one on light chain, other at myosin head
Smooth muscle relaxation
With the inactivation of MLCK, a phosphatase is activated. This phosphatase will remove the Pi from the myosin light chain and allow relaxation
The importance of latch mechanism?
Decreases energy utilization by smooth muscle
Makes up for additional ATP used to phosphorylate the light chain in each cycle of smooth muscle contraction
Passive tension in smooth muscle
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
Actin-myosin in smooth muscle
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