BIPN 100 Lecture 20: BIPN 100 Lecture 20
13 Jun 2018
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BIPN 100 Lecture 20
5/21/2018
• Depolarization starts at SA node, goes through gap junction of contractile cells and
through the internodal pathways to the AV node
o The electrical event of depolarization must happen before anything mechanical
(contraction) can happen
• AV node is the only place where the signal can propagate from the atria to the ventricles
due to the connective fibers there, but there is a delay because it takes time for the
small diameters need to sum so that ventricular contraction can happen
• Mechanism of contraction
•
o Happens after the depolarization wave goes through
o Sarcolemma→t-tubules→L-type calcium channels (are voltage gated) moving
calcium from a higher to lower concentration in the ECF to the ICF
o Calcium goes into the cell and causes calcium-induced calcium release
o Activates RYR2 of the SERCA
o This allows calcium to move from the sarcoplasmic reticulum into the cell
o This all causes the calcium signal, when calcium binds to troponin, moving
tropomyosin out of the way, so the myosin head can bind to actin and for a
cross-bridge
o The myosin head has the ATPase and causes a power stroke, shortening the
sarcomere by the muscle filaments sliding towards each other
• Mechanism of relaxation
o Calcium needs to be moved out of the compartment, and into the ECF
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