Ventricular Action Potential | Cardiac Action Potential | Part 1 | Phases | Cardiac Physiology

Summary

This video explains the cardiac action potential, focusing on the phases of the ventricular action potential. It covers how ions like sodium, potassium, and calcium move through different channels to create the action potential's distinct phases: depolarization, initial repolarization, plateau, late repolarization, and resting phase. The video also discusses the refractory periods and their role in preventing repeated action potentials. Additionally, it explains excitation-contraction coupling and how action potentials propagate through gap junctions, ensuring synchronized heart contractions. A deeper dive into the sinoatrial node will be explored in Part 2.

Takeaways

• 😀 Cardiac action potentials differ from those in neurons and skeletal muscles, with unique phases and a plateau in ventricular muscle cells.
• 😀 The ventricular action potential includes five phases: depolarization (phase 0), initial repolarization (phase 1), plateau (phase 2), repolarization (phase 3), and resting membrane potential (phase 4).
• 😀 Action potentials are brief changes in membrane potential caused by ion movements (sodium, potassium, and calcium), which carry charges and alter the membrane potential.
• 😀 Neurons have a resting membrane potential of about -70mV, while cardiac muscle cells have a more negative resting potential of around -90mV.
• 😀 In neurons, action potentials involve the movement of sodium and potassium ions, resulting in depolarization, repolarization, and hyperpolarization.
• 😀 Cardiac muscle cells experience depolarization due to sodium and calcium influx, followed by a repolarization phase due to potassium efflux, creating a prolonged action potential.
• 😀 The plateau phase of the cardiac action potential is caused by a balance of calcium influx and potassium efflux, allowing sustained depolarization.
• 😀 Potassium channels contribute to repolarization during phase 3 of the cardiac action potential, with the membrane returning to the resting potential in phase 4.
• 😀 Similar to neurons, cardiac cells undergo a refractory period, during which a second stimulus cannot trigger another action potential, ensuring coordinated heart contractions.
• 😀 The process of excitation-contraction coupling occurs in contractile cardiac muscle cells, where calcium influx triggers muscle contraction by interacting with the sarcoplasmic reticulum.
• 😀 Cardiac action potentials spread through gap junctions to ensure synchronized contraction of heart muscle cells in the atria and ventricles.

Q & A

What is the main focus of the video?

The video focuses on explaining the cardiac action potential, particularly the ventricular action potential in part one. It also briefly mentions the sinoatrial node, which will be covered in part two.

How do cardiac action potentials differ from those in nerves and skeletal muscles?

Cardiac action potentials have distinct phases, including a plateau phase, unlike the action potentials in nerves and skeletal muscles, which are simpler and do not have this plateau.

What are the five phases of the ventricular cardiac action potential?

The five phases are: phase 0 (depolarization), phase 1 (initial repolarization or the notch), phase 2 (plateau), phase 3 (late repolarization), and phase 4 (resting membrane potential).

What ions are involved in the cardiac action potential and what are their roles?

The main ions involved are sodium (Na+), potassium (K+), and calcium (Ca2+). Sodium and calcium enter the cell during depolarization, while potassium exits the cell during repolarization.

How does the plateau phase in the cardiac action potential occur?

The plateau phase occurs due to the balance between the entry of calcium ions into the cell and the exit of potassium ions. This balance results in sustained depolarization.

What causes the upstroke of the cardiac action potential?

The upstroke is primarily caused by the rapid entry of sodium ions through fast sodium channels, making the inside of the cell less negative and more positive.

What happens during the repolarization phase of the cardiac action potential?

During repolarization, potassium ions leave the cell, making the membrane potential more negative, while calcium channels slowly close, contributing to the decrease in the positive charge.

What is the absolute refractory period in the cardiac action potential?

The absolute refractory period is the phase during which no new action potential can be triggered, no matter how strong the stimulus is, because sodium channels are inactivated.

How does the relative refractory period differ from the absolute refractory period?

In the relative refractory period, a second action potential can be initiated, but it requires a stronger-than-usual stimulus, as the cell is almost repolarized but not fully.

What role does calcium play in muscle contraction during the cardiac action potential?

Calcium enters the cell during the plateau phase, stimulating a receptor on the sarcoplasmic reticulum. This triggers the release of more calcium, which leads to muscle contraction through excitation-contraction coupling.