[#1] POTENCIAIS DE AÇÃO CARDÍACO: POTENCIAL DE AÇÃO RÁPIDO (RESPOSTA RÁPIDA) | MK Fisiologia

Summary

This video, hosted by Miriam Curauch from MK Physiology, explores the action potentials of heart muscle fibers, comparing them to skeletal muscle. While both are striated, cardiac fibers have a longer depolarization phase. The video explains the phases of cardiac action potentials, including depolarization, rapid repolarization, and the calcium-potassium balance during the plateau phase. It emphasizes the role of calcium in heart contraction and explains why heart muscle action potentials are different from skeletal muscles and neurons. The video concludes by introducing the unique properties of auto-rhythmic heart cells.

Takeaways

• 💓 The cardiac muscle, like skeletal muscle, is striated due to the organization of thin and thick filaments forming sarcomeres, but the action potential of cardiac fibers differs.
• ⏱️ Cardiac muscle cells have a longer duration of depolarization compared to skeletal muscle cells, which have short action potentials similar to neurons.
• 🔬 The action potential in skeletal muscle involves three phases: depolarization due to sodium channels, repolarization due to potassium channels, and hyperpolarization due to slow potassium channel inactivation.
• 🫀 In cardiac muscle, there are five phases of the action potential, including a plateau phase (phase 2) that lasts about 100-200 milliseconds, due to the balance between potassium efflux and calcium influx.
• 🚀 The long duration of the plateau phase in cardiac action potential is due to the interplay between potassium and calcium ions, maintaining a stable membrane potential.
• 🔋 The opening and closing of voltage-gated ion channels specific to sodium, potassium, and calcium ions explain the action potential in cardiac fibers.
• 🌀 The action potential in cardiac fibers begins with the rapid depolarization phase (phase 0), followed by rapid repolarization (phase 1), the plateau (phase 2), and then complete repolarization (phase 3) back to the resting potential (phase 4).
• 🛠️ The resting membrane potential of cardiac fibers is maintained near the potassium equilibrium potential, around -90 millivolts, due to the continued opening of potassium channels.
• 💡 The automatic generation of action potentials in the sinoatrial (SA) node, composed of autorhythmic cells, initiates the heartbeat without external stimuli.
• ⏲️ The SA node's autorhythmic cells generate a slower depolarization (phase 0) compared to the rapid depolarization in cardiac fibers, resulting in a slower or 'response slow' action potential.

Q & A

What is the main difference between the action potential of cardiac muscle and skeletal muscle?

The main difference is that the action potential of cardiac muscle lasts much longer than that of skeletal muscle, which is similar to the action potential in neurons. This is due to the different ion channels involved and their dynamics during the action potential phases.

How many phases are there in the action potential of cardiac muscle fibers?

There are five phases in the action potential of cardiac muscle fibers: phase 0 (depolarization), phase 1 (rapid repolarization), phase 2 (plateau), phase 3 (final repolarization), and phase 4 (resting potential).

What causes the plateau phase in the action potential of cardiac muscle?

The plateau phase, or phase 2, is caused by the balance between the outward movement of potassium ions and the inward movement of calcium ions through their respective voltage-dependent channels, which stabilizes the membrane potential.

What is the role of calcium ions in the action potential of cardiac muscle?

Calcium ions play a crucial role by entering the cell through slow calcium channels during phase 2, contributing to the plateau phase. Additionally, the influx of calcium ions triggers the contraction of cardiac muscle fibers.

How does the resting membrane potential of cardiac muscle fibers differ from that of skeletal muscle?

The resting membrane potential of cardiac muscle fibers is closer to the equilibrium potential of potassium, around -90 millivolts, due to the higher permeability of the membrane to potassium ions.

What is the significance of the sodium-potassium pump in the context of cardiac muscle action potentials?

The sodium-potassium pump maintains the concentration gradient of ions across the cell membrane, which is essential for the generation and maintenance of action potentials in cardiac muscle fibers.

What is the role of the 'pacemaker' cells in the heart, and how do they differ from other cardiac muscle cells?

Pacemaker cells, found in the sinoatrial node, are self-excitable and can generate action potentials spontaneously without external stimulation. Their action potentials are slower in phase 0 compared to other cardiac muscle cells, and they are known as slow response or slow action potentials.

Why is the action potential of pacemaker cells different from that of the rest of the cardiac muscle?

The action potential of pacemaker cells is different because they have a unique ion channel composition and dynamics that allow for spontaneous depolarization, leading to the generation of slow action potentials.

How does the intercalated disc play a role in the propagation of action potentials in cardiac muscle?

Intercalated discs are specialized structures that electrically couple cardiac muscle cells, allowing the rapid and coordinated propagation of action potentials throughout the heart.

What is the threshold potential for cardiac muscle cells, and what happens when it is reached?

The threshold potential for cardiac muscle cells is around -65 millivolts. When this potential is reached, it triggers the opening of fast sodium channels, leading to the rapid depolarization phase of the action potential.