What are the phases of the cardiac action potential?

How many phases are in cardiac action potential?

The cardiac action potential has five phases as shown in Fig. 2. During phase 0, membrane permeability to potassium decreases and fast sodium channels open, producing rapid depolarization from −90 mV to +10 mV.

What are the four phases of action potential?

It consists of four phases; hypopolarization, depolarization, overshoot, and repolarization. An action potential propagates along the cell membrane of an axon until it reaches the terminal button.

What happens during phase 4 of the cardiac action potential?

In these cells, phase 4 is also known as the pacemaker potential. During this phase, the membrane potential slowly becomes more positive, until it reaches a set value (around -40 mV; known as the threshold potential) or until it is depolarized by another action potential, coming from a neighboring cell.

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What are the three phases in order from start to finish that cardiac action potentials are composed of?

The action potential has three main stages: depolarization, repolarization, and hyperpolarization. Depolarization is caused when positively charged sodium ions rush into a neuron with the opening of voltage-gated sodium channels.

What are the 5 steps of an action potential?

The action potential can be divided into five phases: the resting potential, threshold, the rising phase, the falling phase, and the recovery phase.

What are the two types of action potential in the heart?

Key Concept: There are two types of action potentials in the…

  • Fast/long action potentials are produced in working cells and Purkinje fibers. Working cells do not exhibit automaticity, and they lack a spontaneous depolarization to threshold for producing an action potential. …
  • Slow/brief action potentials are produced in the SA & AV nodes.


What happens in an action potential?

An action potential occurs when a neuron sends information down an axon, away from the cell body. … The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event (a stimulus) causes the resting potential to move toward 0 mV.

What is the overshoot in an action potential?

The region of the action potential between the 0 mV level and the peak amplitude is the overshoot. The return of the membrane potential to the resting potential is called the repolarization phase.

Where are action potentials the fastest?

The fastest signals in our bodies are sent by larger, myelinated axons found in neurons that transmit the sense of touch or proprioception – 80-120 m/s (179-268 miles per hour).

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What is phase 4 depolarization?

Phase 4 is the spontaneous depolarization (pacemaker potential) that triggers the action potential once the membrane potential reaches threshold between -40 and -30 mV). Phase 0 is the depolarization phase of the action potential.

Why is it only possible to induce an Extrasystole during relaxation?

Why is it only possible to induce an extrasystole during relaxation? Extrasystole is only possible during relaxation because no new stimulation can take place during the absolute refractory period. Due to this wave summation tetanus can’t be achieved and the extrasystole can’t occur until relaxation.

What are the 4 phases of cardiac cycle?

The cardiac cycle involves four major stages of activity: 1) “Isovolumic relaxation”, 2) Inflow, 3) “Isovolumic contraction”, 4) “Ejection”.

What is the meaning of depolarization?

movement of a cell’s membrane potential to a more positive value (i.e. movement closer to zero from resting membrane potential). When a neuron is depolarized, it is more likely to fire an action potential.

What causes depolarization of cardiac muscle?

In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of fast sodium channels. This also occurs in non-pacemaker cardiac cells; however, in cardiac pacemaker cells, calcium ions are involved in the initial depolarization phase of the action potential.

How do the action potentials rapidly distribute throughout the ventricles?

From the AV node, the action potential spreads rapidly throughout the ventricles, hastended by a specialized ventricular conduction system consisting of the bundle of His and Purkinje fibers. Extends from the SA node within the right atrium to the left atrium.

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Cardiac cycle