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Old 10-07-2012
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Question cardiac muscle cell contraction

while reading an explanation of one question, it got me a bit confused about this...
when the cardiac muscle cell contracts, we have:
1) the action potential that has phases 0,1,2 -platue,3 and 4. and all the voltage gated channels working there including the calcium channels (L-type)

2) also we have the ryanodine receptor path: electrical depolarization opens voltage gated Calcium channels > calcium goes in and activated the ryanodine receptors which allows calcium to come out the sarcoplasmic reticulum, which goes to bind troponin-C which removed tropomyocin from the way so actin and myocin interact and contractions happens..

my question:
A) how can we integrate points 1 and 2? are they happening together? one is first? like, what's the relation between the two events.

b) the voltage gated calcium channels (ones highlighted in purple) in those two points (1 and 2), are they the same?

thanks in advance and good luck to everybody
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Old 05-03-2014
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Cardiac myocytes contraction (Ca+2 Induced Ca+2 Release):

During plateau of ventricular action potential:
Increased Ca+2 conductance, Ca+2 enters the cardiac myocyte (Ca+2 inward current) through voltage-gated L-type Ca+2 channels, also known as dihydropyridine receptors.
This Ca+2 entry triggers the release of even more Ca+2 from SR through Ca+ release channels known as ryanodine receptors.
Intracellular Ca+2 increases leading to myocytes contraction.

The more Ca+2 inward current --> the more Ca+2 released from SR --> the higher intracellular Ca+2 --> the higher the magnitude of tension developed.

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Musculoskeletal-, Physiology-

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