Smooth Muscle

Question 1

Anatomical properties

Answer 1

fusiform
found in walls of viscera and blood vessels
much smaller than skeletal muscle
no striations
one long central nucleus
less sarcoplasmic reticulum
thin actin attached to dense bodies
innervation
under involuntary control
still excitable and contractile
slightly altered myosin-actin arrangement
attachment plaques hold cells together
may be linked by gap junctions

Question 2

Physiological properties

Answer 2

longer actin and myosin filaments push antiparallel
myosin ATPase activity is much slower
myosin light chain plays regulatory role
different Ca mechanism

Question 3

Smooth is like skeletal

Answer 3

it is muscle
has actin and myosin
does contract
may be innervated

Question 4

smooth is unlike skeletal

Answer 4

different locations
shorter fusiform fibers
uni-nucleated
no striations
less sarcoplasmic reticulum
involuntary

Question 5

Contraction

Answer 5

1. intracellular Ca conc. increases when Ca enters the cell and is released from SR
2. Ca binds to Calmodulin (Ca sensor)
3. Ca-calmodulin activates myosin light chain kinase (MLCK)
4. MLCK phosphorylates light chain in myosin heads and increases myosin ATPase activity
5. active myosin crossbridges slide on actin and create tension

Question 6

What is the role of myosin light chain

Answer 6

speed up myosin heavy chain/ myosin ATPase

Question 7

Protein phosphorylation

Answer 7

post-translational modifications may dictate protein shape, activity, stability, binding partners or localization

Question 8

What do phosphatase and De phosphorylation do

Answer 8

de-activate proteins

Question 9

what do kinase and phosphorylation do

Answer 9

activate proteins

Question 10

Relaxation

Answer 10

1. free Ca in cytosol decreases when Ca is pumped out of cell/back into SR
2. Ca unbinds from Calmodulin
3. myosin phosphatase removes phosphate from myosin, decreasing myosin ATPase activity
4. less myosin ATPase results in decreased muscle tension

Question 11

Action Potentials

Answer 11

Time course of AP is seconds
slow wave potentials
pacemaker potentials
pharmomechanical couplic potentials

Question 12

slow wave potentials

Answer 12

fire APs IF they reach threshold

Question 13

pacemaker potentials

Answer 13

always depolarize to threshold

Question 14

pharmomechanical couplic potentials

Answer 14

occurs when chemical signals change muscle tension through signal transduction pathways with little to no change in membrane potential

Question 15

Contraction comparison

Answer 15

skeletal contraction is quick
cardiac contraction is slightly slower
smooth contraction is much slower