The plateau phase of an action potential in cardiac muscle cells is due to the


The cardiac muscle cell action potential

The cardiac muscle cell action potential is a brief electrical change that occurs in cardiac muscle cells. This electrical change is caused by the movement of ions across the cell membrane. The cardiac muscle cell action potential is important because it is responsible for the contraction of cardiac muscle cells.

The plateau phase

After the peak of the action potential has been reached, there is a period of time when the membrane potential remains at a constant, or plateau, level before it starts to repolarize. This plateau phase is caused by the opening of Ca2+ channels. The influx of Ca2+ during this phase causes an increased release of Ca2+ from the sarcoplasmic reticulum, which amplifies and prolongs the action potential. In cardiac muscle, this plateau phase is particularly important in ensuring that the heart contracts strongly and efficiently.

The role of calcium


Cardiac muscle cells are unique in that they are able to generate their own action potentials, which triggers contraction of the heart. This is made possible by the presence of special membrane proteins called channels, which allow ions to flow in and out of the cell.

One key ion involved in cardiac muscle contraction is calcium. Inside cardiac muscle cells, there is a small concentration of calcium ions compared to the extracellular fluid. When the cell is at rest, calcium ions are kept out of the cell by a protein called the sodium-calcium exchanger.

When the cell is stimulated and an action potential begins, calcium channels open and calcium rushes into the cell. This increase in calcium concentration inside the cell causes the cardiac muscle fibers to contract.

The plateau phase in other cell types

The plateau phase in cardiac muscle cells is due to the

Skeletal muscle cells


The plateau phase in other cell types – (the plateau phase of an action potential in cardiac muscle cells is due to the)

Skeletal muscle cells – The plateau phase in skeletal muscle cells is due to the activation of voltage-dependent calcium channels. These channels are not activated during the early part of the action potential, but are gradually activated as the potential difference reaches a threshold value. The influx of calcium through these channels causes an increase in the intracellular calcium concentration, which leads to an increased force of contraction.

Cardiac muscle cells – The plateau phase of an action potential in cardiac muscle cells is due to the activation of voltage-dependent potassium channels. These channels are not activated during the early part of the action potential, but are gradually activated as the potential difference reaches a threshold value. The efflux of potassium through these channels causes a decrease in the intracellular potassium concentration, which leads to a decreased force of contraction.

Smooth muscle cells – The plateau phase in smooth muscle cells is due to the activation of voltage-dependent calcium channels. These channels are not activated during the early part of the action potential, but are gradually activated as the potential difference reaches a threshold value. The influx of calcium through these channels causes an increase in the intracellular calcium concentration, which leads to an increased force of contraction.

Smooth muscle cells


In other cell types the plateau phase may be preceded by a delay, during which thecell membrane is impermeable to sodium. For example, in skeletal muscle cells,the Electrical activity started well before any change in muscle length wasnoticed (Figure 1). In cardiac muscle, there is also a delay of about 0.3 secondsbefore contraction begins. This pre-excitation time is due to the propagationof electrical activity from the atria to the ventricles through the atrioventricular(AV) node. After the delay, CONTRACTION begins and force is developedwith no further change in muscle length (the plateau phase). Finally, relaxationbegins, again with no change in muscle length

In smooth muscle cells there is no such delay before contraction begins. Thisis because in smooth muscle cells, electrical activity spread much more slowlythan in skeletal or cardiac muscle cells (about 0.1 mm/second comparedwith 10 m/s in skeletal muscles and 100 m/s in cardiac muscles). As aresult, by the time an electrical stimulus has reached all regions of a smoothmuscle cell, some regions may have already started to contract

The clinical implications of the plateau phase

The plateau phase of an action potential in cardiac muscle cells is a crucial electrical event that maintains the heart’s normal function. A disruption in this phase can lead to arrhythmias, which can be life-threatening. In this article, we will discuss the clinical implications of the plateau phase.

Cardiac arrhythmias

There is a lack of clinical evidence to support the occurrence of the plateau phase in humans. However, animal studies have shown that the plateau phase can lead to cardiac arrhythmias, myocardial infarction, and sudden cardiac death. These findings suggest that the plateau phase may have clinical implications in humans.

Sudden cardiac death

The plateau phase is a period of time during which the level of cardiac output remains static despite changes in the other phases of the cardiac cycle. This phase occurs between the systolic and diastolic phases, and can last for just a few milliseconds or up to several seconds. Although it is a relatively short period of time, the plateau phase is important as it determines the size of the final heart beat.

The main clinical implication of the plateau phase is sudden cardiac death. This occurs when the heart abruptly stops beating, usually due to Ventricular Fibrillation (VF). VF is a condition where the electrical activity of the heart becomes chaotic, causing the heart to stop pumping blood around the body. This can lead to death within minutes if not treated immediately.

The plateau phase is also important in terms of diagnosis and treatment of other cardiac conditions such as acute myocardial infarction (heart attack) and heart failure. By understanding how different factors influence the length and stability of the plateau phase, clinicians can better assess and treat these conditions.


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