How are action potentials propagated in the heart?

How are action potentials propagated in the heart?

Action potentials from the SA node propagate to the atria. From there, the impulse travels to the atrioventricular (AV) node and through specialized conduction fibers (Purkinje fibers) into the ventricular muscle.

How do class I antiarrhythmics work?

Class 1a antiarrhythmics inhibit the Na+ channels and the K+ channels on atrial and ventricular myocytes and cells of the purkinje fibers. When Na+ channels are blocked, it decreases the amount of sodium entering the cell so this causes a slower depolarization, which means a decrease in the slope during phase 0.

Where will action potentials propagate after the AV node?

After crossing the AV node, the impulse spreads into the rapidly conducting bundle of His and through the bundle branches to the Purkinje fibers. The electrical impulse is distributed throughout the bulk of the ventricular myocyte for precisely timed stimulation and contraction of the ventricles.

Why is it called Funny Channel?

Funny current (or funny channel, or If) refers to a specific current in the heart. It is called “funny” because it has effects opposite to those of most other heart currents. Funny currents have been associated with cyclic-nucleotide-gated channels.

What happens if Na channels are blocked?

Complete block of sodium channels would be lethal. However, these drugs selectively block sodium channels in depolarized and/or rapidly firing cells, such as axons carrying high-intensity pain information and rapidly firing nerve and cardiac muscle cells that drive epileptic seizures or cardiac arrhythmias.

How long does it take for antiarrhythmics to work?

This medication must be taken regularly for one to three weeks before a response is seen and for several months before the full effect occurs.

How is action potential propagation different in cardiac muscle cells than in skeletal muscle cells?

Cardiac action potentials in the heart differ considerably from action potentials found in neural and skeletal muscle cells. One major difference is in the duration of the action potentials. In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of fast sodium channels.

How do antiarrhythmic drugs affect cardiac action potentials?

All antiarrhythmic drugs directly or indirectly alter membrane ion conductances, which in turn alters the physical characteristics of cardiac action potentials. For example, some drugs are used to block fast sodium channels. These channels determine how fast the membrane depolarizes (phase 0) during an action potential.

How do antiarrhythmics stabilize the cell membrane?

Class I antiarrhythmics stabilize cell membrane by depressing phase 0 of action potential. They bind to sodium channels and change the duration of action potential of the cells. Class Ia drugs depress phase 0 and prolong duration of action potential.

What are the modes of action of antiarrhythmic drugs?

The classic work defined 4 major possible modes of action of antiarrhythmic drugs variously modifying Na +, K +, and Ca 2+ channel function and intracellular mechanisms regulated by adrenergic activity.

Are there any antiarrhythmics that are proarrhythmic?

Several classes of antiarrhythmics, including , also have other medical uses, which are discussed in their respective articles. . All antiarrhythmic drugs are also potentially proarrhythmic! Intravenous administration should only be performed with ! opyramide. “LInDO MEXIco Is the Best”: LIDOcaine and MEXIletine are class IB antiarrhythmic drugs.