Pacemaker potencial

Pacemaker is designation for cells, that spontaneously generate an action potential. This ability is called autorythmicity. Pacemaker cells are typically used in cardiac conduction system, where they produce a heart rhythm.

Spontaneous diastolic depolarization
Resting membrane potencial does not occur in sinoatrial and atrioventricular node cells. Instead, each action potential is preceded by a gradual change of the membrane potential towards a threshold value. This process is called spontaneous diastolic depolarization and depends on the autonomic nervous system.

The principle of the process is the movement of the following ions.
 * Na+ intracellularly
 * Ca2+ intracellularly
 * reduced current K+ extracellularly

Na+ ions pass into the cell through 'funny channels' and are less important in terms of overall depolarization. Ca2+ ions have the largest share in the development of spontaneous diastolic depolarization. Ca2+ influx occurs through specific channels. The influx of calcium ions causes a gradual depolarization and subsequent formation of the action potential. The last of these is the reduction of the flow of K+ out of the cell. This gradual inactivation plays a crucial role in the development of spontaneous diastolic depolarization - under normal circumstances, the current K+is responsible for maintaining the resting membrane potential.

Formation of the electrical impulses
Physiologically, the sinoatrial (SA) node is responsible for generating the electrical impulses. Of all the other parts of the transmission system, its membrane potential is closest to the threshold, and thus forms the action potential first. This node acts as a primary (natural) pacemaker and the rhythm it specifies is called a sinus rhytm. Under pathological conditions, the pacemaker is taken over by a atrioventricular (AV) node, or by a cell of the transmission system (most often Purkinje fibers) - the resulting pacemaker is called an ectopic pacemaker. The rhythm generated by the AV node is called nodal, the Purkinje fibers generate the idioventricular rhythm.

Regulation of pacemaker potential
Pacemaker potential formation is primarily controlled by the autonomic nervous system nervovým systémem. Sympatic causes increased influx of Ca 2+ and Na + into cell and at the same time inactivates K+ channels and thus prevents the efflux of ions from the cell - this leads to a faster course of spontaneous diastolic depolarization. The effect of parasympathetic is exactly the opposite. Given that the SA node generates at rest approximately 100 stimuli per minute[1], the parasympathetic nerve must predominate at a resting frequency of 60-80 beats per minute

Related articles

 * Heart
 * Action potential in heart
 * Resting Membrane Potential
 * Conduction system of the heart
 * Elektrokardiography

Literature

 * KITTNAR, Otomar, et al. Lékařská fyziologie. 1. vydání. Praha : Grada, 2011. 790 s.  ISBN 978-80-247-3068-4.


 * SILBERNAGL, Stefan a Agamemnon DESPOPOULOS. Atlas fyziologie člověka. 6. vydání. Praha : Grada, 2003. 435 s.  ISBN 80-247-0630-X.