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      • In the pacemaking cells of the heart (e.g., the sinoatrial node), the pacemaker potential (also called the pacemaker current) is the slow, positive increase in voltage across the cell's membrane, that occurs between the end of one action potential and the beginning of the next. It is responsible for the self-generated rhythmic firing (automaticity) of pacemaker cells.


      Background



      The cardiac pacemaker is the heart's natural rhythm generator. It employs pacemaker cells that generate electrical impulses, known as cardiac action potentials. These potentials cause the cardiac muscle to contract, and the rate of which these muscles contract determines the heart rate.
      As with any other cells, pacemaker cells have an electrical charge on their membranes. This electrical charge is called the membrane potential. After the firing of an action potential, the pacemaking cell's membrane repolarizes (decreases in voltage) to its resting potential of -60 mV. From here, the membrane gradually depolarizes (increases in voltage) to the threshold potential of -40 mV, upon which the cell would go on to fire the next action potential. The rate of depolarization is the slope: the faster voltage increases, the steeper the slopes are in graphs. The slope determines the time taken to reach the threshold potential, and thus the timing of the next action potential.
      In a healthy sinoatrial node (SAN, a complex tissue within the right atrium containing pacemaker cells that normally determine the intrinsic firing rate for the entire heart), the pacemaker potential is the main determinant of the heart rate. Because the pacemaker potential represents the non-contracting time between heart beats (diastole), it is also called the diastolic depolarization.
      The amount of net inward current required to move the cell membrane potential during the pacemaker phase is extremely small, in the order of few pAs, but this net flux arises from time to time changing contribution of several currents that flow with different voltage and time dependence. Evidence in support of the active presence of K+, Ca2+, Na+ channels and Na+/K+ exchanger during the pacemaker phase have been variously reported in the literature, but several indications point to the “funny”(If) current as one of the most important.(see funny current). There is now substantial evidence that also sarcoplasmic reticulum (SR) Ca2+-transients participate to the generation of the diastolic depolarization via a process involving the Na–Ca exchanger.
      The rhythmic activity of some neurons like the pre-Bötzinger complex is modulated by neurotransmitters and neuropeptides, and such modulatory connectivity gives to the neurons the necessary plasticity to generating distinctive, state-dependent rhythmic patterns that depend on pacemaker potentials.


      Pacemakers



      The heart has several pacemakers, each which fires at its own intrinsic rate:

      SA node: 60–100 bpm
      Atrioventricular node(AVN): 40–60 bpm
      Purkinje fibres: 20–40 bpm
      The potentials will normally travel in order
      SA node → Atrioventricular node → Purkinje fibres
      Normally, all the foci will end up firing at the SA node rate, not their intrinsic rate in a phenomenon known as overdrive-suppression. Thus, in the normal, healthy heart, only the SA node intrinsic rate is observable.


      Pathology


      However, in pathological conditions, the intrinsic rate becomes apparent. Consider a heart attack which damages the region of the heart between the SA node and the AV node.
      SA node → |block| AV node → Purkinje fibres
      The other foci will not see the SA node firing; however, they will see the atrial foci. The heart will now beat at the intrinsic rate of the AV node.


      Induction


      The firing of the pacemaker cells is induced electrically by reaching the threshold potential of the cell membrane. The threshold potential is the potential an excitable cell membrane, such as a myocyte, must reach in order to induce an action potential. This depolarization is caused by very small net inward currents of calcium ions across the cell membrane, which gives rise to the action potential.


      Bio-pacemakers


      Bio-pacemakers are the outcome of a rapidly emerging field of research into a replacement for the electronic pacemaker. The bio-pacemaker turns quiescent myocardial cells (e.g. atrial cells) into pacemaker cells. This is achieved by making the cells express a gene which creates a pacemaker current.


      See also


      Pacemaker action potential
      Graded potential


      References

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    Artikel Terkait "pacemaker potential"

    Pacemaker potential - Wikipedia

    In the pacemaking cells of the heart (e.g., the sinoatrial node), the pacemaker potential (also called the pacemaker current) is the slow, positive increase in voltage across the cell's membrane, that occurs between the end of one action potential and the beginning of the next.

    Sinoatrial Node Action Potentials - CV Physiology

    Cells within the sinoatrial (SA) node are the primary pacemaker site within the heart. These cells are characterized as having no true resting potential, but instead generate regular, spontaneous action potentials.

    Cardiac Pacemaker Cells - Cardiac Cycle - TeachMePhysiology

    17 Jul 2023 · The pacemaker potential is achieved by activation of hyperpolarisation activated cyclic nucleotide gated channels (HCN channels). These allow Na+ entry into the cells, enabling slow depolarisation. These channels are activated when the membrane potential is lower than …

    Physiology, Cardiac Repolarization Dispersion and Reserve

    17 Apr 2023 · Pacemaker cells are highly specialized myocardial cells with an intrinsic ability to depolarize rhythmically and initiate an action potential. The pacemaker cells are located primarily in the SA and atrioventricular (AV) nodes, with some cells also in …

    Cardiac Pacemaker Cells and Action potential • LITFL

    03 Nov 2020 · Draw and describe the cardiac pacemaker action potential and explain the effects of vagal or sympathetic stimulation at the Sino-Atrial (SA) node

    Overview of Cardiac Pacemaker Action Potential

    13 Feb 2016 · Diastolic depolarization (green) (a.k.a.; pacemaker potential) begins at ~-60mV (mean diastolic potential, MDP) as shown on the graph. It initially involves both a gain of sodium ions through membrane channels leading to an interaction between calcium ions from the sarcoplasmic reticulum and external environment with sodium calcium exchangers ...

    Physiology, Cardiac - StatPearls - NCBI Bookshelf

    30 Jul 2023 · The action potential for cardiac pacemaker cells (SA node, AV node, and bundle of His/Purkinje fibers) is unique to the AP of general cardiac myocytes. These cells undergo automaticity and are responsible for the heart rate.

    Cardiac pacemaker cells – Basic Human Physiology

    Unlike skeletal muscles and neurons, cardiac pacemaker cells do not have a stable resting potential. Pacemaker cells contain a series of Na + channels that allow a normal and slow influx of Na + ions that causes the membrane potential to rise …

    Functiogenesis of cardiac pacemaker activity - PMC

    Throughout our investigations on the ontogenesis of the electrophysiological events in early embryonic chick hearts, using optical techniques to record membrane potential probed with voltage-sensitive dyes, we have introduced a novel concept of “functiogenesis” corresponding to “morphogenesis”.

    Pacemaker potential - wikidoc

    In the heart, the pacemaker potential is the voltage created by impulses from an artificial electronic pacemaker or the SA node which drives the rhythmic firing of the heart. The pacemaker potential brings the membrane potential to the threshold potential and initiates an action potential.