Smooth & Cardiac Muscle
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What are the excitation-contraction coupling steps of the cardiac muscle?
- 1) The membrane is depolarized by Na+ entry as an AP begins and opens L-type Ca2+ channels in the T-tubules
- 2) Ca2+ enters the cytosol and binds tom and opens, ryanodine receptor Ca2+ channels in the saracoplasmic reticulum membrane
- 3) Ca2+ flows into the cytosol, raising the Ca2+ concentration. Binding of Ca2+ to troponin exposes cross-bridge cyclign causes force generation and sliding thick and thin filaments
- 4) Cross-bridge cycling causes force generation and sliding of thick and thin filaments
- 5)Ca2+ ATPase pumps return Ca2+ to the sarcoplasmic reticulum and remove Ca2+ from the cell
- 6)The membrane is repolarized when K+ exits to end of the action potential
What events occure after an increase of cytosolic Ca2+ in a smooth muscle fiber?
- 1) Ca2+ binds to calmodulin
- 2)Ca2+-calmodulin complex binds to myosin light-chain kinase
- 3)Active myosin light-chain kinase uses ATP to phosphorylate myosin light chains in the globular head of myosin
- 4)Phosphorylations of myosin drives the cross-bridge away from the think filament backbone, allowing it to bind to actin
- 5) Cross-bridges go through repeated cycles of force generation if myosin light chains are phosphorylated
In muscle, ATP is used:
- is used by myosin ATPase to energize the myosin cross-bridge
- binding to myosin ATPase induced conformation changes that break actin and the myosin bond
- is used for ca transport back to the sarcoplasmic reticulum
The contraction of smooth muscle cells is
a)quick and of short duration
b)is all or none
c) is graded and dependent upon the concentration of calcium
A muscle will ___ if the tension if the tension it develops is greater than the load on it
Some smooth muscles have a membrane potential that spontaneously and rhymically depolarizes. This spontaneous depolarization towards the threshold voltage is known as a -_______.
A condition of smoooth muscle in which persistent cytosolic Ca2+ results in slow ATP hydrolysis and sustained tension is known as the ______ state.
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