Smooth Muscle

Question 1

Smooth muscle characteristics, differences from skeletal

Answer 1

Small, single nucleus, no striations
Poorly developed SR
Membrane with caveoli
Actin and tropomysin (no troponin)
Myosin, ATPase activity is slow

Question 2

Smooth muscle role of calcium, mechanism to allow actin and myosin binding

Answer 2

Ca binds to calmodulin, activates MLCK (myosin light chain kinase)
Phosphorylation of myosin light chain
Dephosphorylation relaxes muscle
Actin attaches to dense bodies/adherens junctions

Question 3

Difference in contraction of smooth muscle

Answer 3

Cycling of myosin cross-bridges is slower than skeletal
Time myosin and actin are attached is greater- which leads to greater force, and less ATP demand
This is known as latch mechanism

Question 4

Mechanism of contraction

Answer 4

Calcium enters from ECF, some is released from SR
IP3 gated Ca release channels and ryanodine receptors play a role as well
MLCK is activated
Myosin light chain phosphorylated, binds actin

Question 5

Important neurotransmitters effecting smooth muscle

Answer 5

Norepi/epi
Ach- contraction is direct, relaxation can be indirect
Angiontensin II, vasopressin, endothelin - contraction
Adenosine- relaxation
NO- relaxation

Question 6

Examples of environmental clues to smooth muscle

Answer 6

Hypoxia
Excess CO2
Increased H+
Adenosine, LA, increased K+

Question 7

Smooth muscle action potentials

Answer 7

Only occur in unitary smooth muscle

Graded potentials are common

Question 8

Spike potentials

Answer 8

Stimulated by hormones, NTs, stretch, or spontaneous

Question 9

Slow waves

Answer 9

Oscillating influx of calcium and efflux of potassium cause deviations in membrane potentials

Question 10

Latch mechanism

Answer 10

Way to increase tension while decreasing ATP usage
Dephosphorylation of light chain
Cycle proceeds slowly- increases time of contraction
Attached cross bridges are still generating tension