Action Potential in Cardiac Muscle | Cardiac Physiology | Electrophysiology

Understanding Action Potential in Cardiac Muscle

Introduction to Action Potential

• The video introduces the concept of action potential in cardiac muscle, highlighting its complexity for undergraduates and encouraging viewers to watch until the end for clarity.

Components of Action Potential

• The speaker emphasizes that action potential in cardiac muscle differs significantly from that in skeletal muscle or nerve fibers. Understanding resting membrane potential is crucial before delving into action potentials.

Resting Membrane Potential

• The resting membrane potential in cardiac muscle is identified as -90 millivolts. Key terms such as depolarization (inside becoming more positive) and repolarization (inside becoming more negative) are defined.

Phases of Action Potential

• Four phases of action potential are outlined:

• Phase 0: Rapid depolarization.

• Phase 1: Initial rapid repolarization.

• Phase 2: Plateau phase with minimal change in membrane potential.

• Phase 3: Repolarization phase returning to resting state.

Ionic Basis of Phases

• During Phase 0, voltage-gated sodium channels open, leading to sodium influx and rapid depolarization, peaking at +20 millivolts before these channels close.

• Potassium channels open rapidly causing potassium efflux, contributing to initial rapid repolarization.

Plateau Phase Dynamics

• In Phase 2, L-type calcium channels open allowing calcium influx while delayed rectifier potassium channels also allow potassium efflux; this balance results in a plateau phase where membrane potential remains stable.

Final Repolarization Phase

Understanding Cardiac Action Potentials

Phases of Cardiac Action Potential

• Phase Zero: Rapid Depolarization

• This phase is characterized by the rapid opening of sodium channels, leading to a significant influx of sodium ions into the cell.

• Phase One: Initial Rapid Repolarization

• Sodium channels that were open during depolarization close quickly, halting sodium influx.

• Concurrently, potassium channels open and close rapidly, causing a brief efflux of potassium ions which contributes to initial repolarization.

• Phase Two: Plateau Phase

• The opening of L-type calcium channels initiates calcium influx into the cell.

• Another type of potassium channel, known as delayed rectifier potassium channels, also opens. This results in a balance between positive ions moving in (calcium) and out (potassium), stabilizing the membrane potential.

• Phase Three: Slow Repolarization

• L-type calcium channels begin to close, stopping further calcium influx.

• Delayed rectifier potassium channels remain open, allowing for continued potassium efflux which leads to further repolarization.

• Continued Repolarization Mechanisms