What causes the depolarization phase of a pacemaker action potential?

What causes the depolarization phase of a pacemaker action potential?

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.

What ion causes depolarization in pacemaker cells?

This gradual depolarization mainly occurs via a depolarization current or pacemaker current (If). Pacemaker current occurs due to the slow influx of Na+ ions through the hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel).

How do pacemaker cells depolarize?

Cells within the sinoatrial (SA) node are the primary pacemaker site within the heart. 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.

Is action potential polarization and depolarization?

Resting potential gives the neuron a break. When the neuron is inactive and polarized, it’s said to be at its resting potential. This causes complete depolarization of the neuron and an action potential is created. In this state, the neuron continues to open Na+ channels all along the membrane.

What do pacemaker cell action potentials lack?

What do pacemaker cell action potentials lack? the length or degree of stretch of the sarcomeres in the ventricular cells before they contract. the force the ventricles must overcome to eject blood into their respective arteries. the amount of blood that has drained into the ventricle by the end of the filling phase.

What is depolarization in ECG?

Atrial depolarization is reflected by the P wave, and ventricular depolarization is reflected by the QRS complex, whereas the T wave reflects ventricular repolarization, see Figure 6.10. Atrial repolarization cannot usually be discerned from the ECG since it coincides with the much larger QRS complex.

Why do pacemaker cells depolarize slowly?

In all other cells, the resting potential (-60mV to -70mV) is caused by a continuous outflow or “leak” of potassium ions through ion channel proteins in the membrane that surrounds the cells. However, in pacemaker cells, this potassium permeability (efflux) decreases as time goes on, causing a slow depolarization.

What triggers action potentials in pacemaker cells?

The firing of the pacemaker cells is induced electrically by reaching the threshold potential of the cell membrane. This depolarization is caused by very small net inward currents of calcium ions across the cell membrane, which gives rise to the action potential.

Why are cardiac action potentials longer?

The action potentials of ventricular myocytes are distinct from those of neurons in that they are longer in duration with a plateau in depolarization. This prolonged depolarization is necessary to give myocytes adequate time to contract and to synchronize their contraction to maximize pumping efficiency.