1. Excitation contraction coupling in cardiac muscle occurs by: a) Ca induced Ca

Question

1. Excitation contraction coupling in cardiac muscle occurs by:

a) Ca induced Ca release from the SR that is triggered by Ca flow thru L-type Ca Sarcolemma receptors

b) Ca induced Ca release from the SR that is triggered by Ca flow thru the ryanodine receptors of the sarcolemma

c) A molecular link between the L-type Ca T-tubule receptor and the SR ryanodine receptor

d) Exchange of 3 sodium ions for 1 Ca ion across the sarcolemma via the sodium/calcium pump

2. According to the Law of LaPlace, if the radius of a ventricular chamber increases and the wall tension stays the same then:

a) Chamber pressure will rise

b) Chamber pressure will drop

c) Maximum developed force will increase

d) Maximum developed force will decrease

e) Chamber pressure will rise and developed force will increase

Explanation / Answer

Please find the answers below:

Part 1: Choice b (cardiac muscles contract and relax rhythemically and their rhythemic contractibility is highly coupled to intracellular calcium concentrations. This hold true for both cytoplasmic and organellar caclium concentrations of calcium in a cardiac muscle cell. The extracellular calcium moves inside the cell via the L-type calcium channels and modulate the intracellular calcium levels by controlling release of store-operated calcium concentrations in the endoplasmic reticulum by ryanodine receptors)

Part 2: Choice b (According to LaPlace law, if a vessels comprises of fluid filled inside it and the flow of fluid increases hence pressure increases, then the vessel walls experience more wall-tension to withstand the increased vessel pressure, i.e. in general:

Tension = (Pressure * Radius)/2

Thus, if the radius of a ventricular chamber increases, and the wall tension remains same, then the quantity Pressue must decrease to keep the value constant. )

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