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The action potential passes along the cell membrane causing the cell to contract, therefore the activity of the sinoatrial node results in a resting heart rate of roughly 60–100 beats per minute. All cardiac muscle cells are electrically linked to one another, by intercalated discs which allow the action potential to pass from one cell to the ...
The plateau lasts on the order of 100 ms. At the time that calcium channels are getting activated, channels that mediate the transient outward potassium current open as well. This outward potassium current causes a small dip in membrane potential shortly after depolarization. This current is observed in human and dog action potentials, but not ...
Depolarization is essential to the function of many cells, communication between cells, and the overall physiology of an organism. Action potential in a neuron , showing depolarization, in which the cell's internal charge becomes less negative (more positive), and repolarization, where the internal charge returns to a more negative value.
The cells that make up the SA node are specialized cardiomyocytes known as pacemaker cells that can spontaneously generate cardiac action potentials. These signals are propagated through the heart's electrical conduction system. [1] [2] Only one percent of the heart muscle cells are conductive, the rest of the cardiomyocytes are contractile.
However, some excitable cells require no such stimulus to fire: They spontaneously depolarize their axon hillock and fire action potentials at a regular rate, like an internal clock. [32] The voltage traces of such cells are known as pacemaker potentials. [33] The cardiac pacemaker cells of the sinoatrial node in the heart provide a good example.
The heart is a functional syncytium as opposed to a skeletal muscle syncytium. In a functional syncytium, electrical impulses propagate freely between cells in every direction, so that the myocardium functions as a single contractile unit. This property allows rapid, synchronous depolarization of the myocardium.
Afterdepolarizations may lead to cardiac arrhythmias. Afterdepolarization is commonly a consequence of myocardial infarction, cardiac hypertrophy, or heart failure. [1] It may also result from congenital mutations associated with calcium channels and sequestration. [2]
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.