Increased [Ca2+]cyt activates plasma membrane anion efflux channels, and these two effects combine to depolarize the membrane. Membrane depolarization closes voltage‐sensitive K+ in channels but opens K+ out channels. 

TLS Online TPP Program

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#Unit 7. System Physiology – Animal

The action potential spreads throughout the myocardium in the following sequence:

SA node  Atrial internodal tracts and atria  AV node  Bundle of His  Purkinje system  Ventricles

TLS Online TPP Program

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#Unit 7. System Physiology – Animal

Myocardial fibers have a resting membrane potential of approximately –90 mV.

TLS Online TPP Program

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#Unit 7. System Physiology – Animal

The individual fibers are separated by membranes, but depolarization spreads radially (syncytium) because of the presence of gap junctions.

TLS Online TPP Program

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#Unit 7. System Physiology – Animal

In cardiac muscle, the action potential is caused by opening of three types of channels: 

Voltage activated fast sodium channels 

L-type calcium channels (slow calcium channels or calcium-sodium channels)

Voltage activated potassium ion channels

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#Unit 7. System Physiology – Animal

Phase 0 (depolarization), fast sodium channels open. 

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#Id: 5264

#Unit 7. System Physiology – Animal

Phase 1 (initial repolarization), fast sodium channels close.