Pacemaker potential

Pacemaker potential‏‎ is the ability of certain types of cardiac cells to spontaneously create an electrical impulse. These cells are found in the sinoatrial node (SA node) and the atrioventricular node (AV node) of the heart. The pacemaker potential is the basis for the heart's rhythmic, autonomous contractions.

Mechanism

The pacemaker potential is initiated by the slow, spontaneous depolarization of the cell membrane of the pacemaker cells. This depolarization is due to two main factors: the slow inward current of sodium ions (Na+) and the slow outward current of potassium ions (K+).

The pacemaker potential begins at the end of the previous action potential. At this point, the membrane potential is at its most negative. The slow inward current of Na+ ions through the funny current channels (also known as HCN channels) begins to depolarize the membrane. This is the first phase of the pacemaker potential.

As the membrane potential becomes less negative, the T-type calcium ion (Ca2+) channels open, allowing a rapid influx of Ca2+ ions. This further depolarizes the membrane, leading to the second phase of the pacemaker potential.

When the membrane potential reaches a threshold, the L-type Ca2+ channels open. This causes a rapid influx of Ca2+ ions, leading to the upstroke of the action potential. This is the third phase of the pacemaker potential.

Following the action potential, the K+ channels open, allowing an outward current of K+ ions. This repolarizes the membrane, returning it to its most negative potential and beginning the cycle anew.

Role in Heart Function

The pacemaker potential plays a crucial role in the function of the heart. It is responsible for the heart's automaticity, or its ability to generate a rhythmic, spontaneous heartbeat. The rate of the pacemaker potential determines the heart rate. Changes in the rate of the pacemaker potential can lead to arrhythmias, or irregular heart rhythms.

See Also

• Cardiac action potential
• Electrophysiology
• Heart rate
• Arrhythmia

References

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