What is cardiac action potential duration?
In a typical nerve, the action potential duration is about 1 ms. In skeletal muscle cells, the action potential duration is approximately 2-5 ms. In contrast, the duration of cardiac action potentials ranges from 200 to 400 ms.
What is the duration of the refractory period in cardiac muscle?
250ms
After an action potential initiates, the cardiac cell is unable to initiate another action potential for some duration of time (which is slightly shorter than the “true” action potential duration). This period of time is referred to as the refractory period, which is 250ms in duration and helps to protect the heart.
Where is action potential fastest in the heart?
Other than the SAN, the AVN and purkinje fibres also have pacemaker activity and can therefore spontaneously generate an action potential. However, these cells usually do not depolarize spontaneously, simply because, action potential production in the SAN is faster.
Why is cardiac action potential prolonged?
During phase 1, there is partial repolarization, because of a decrease in sodium permeability. Phase 2 is the plateau phase of the cardiac action potential. Membrane permeability to calcium increases during this phase, maintaining depolarization and prolonging the action potential.
What affects duration of action potentials?
For example, abnormality of the protein channels inside the cell membrane directly affects the movement of ions entering and exiting the cell, thereby changing the action potential duration (APD) [3]. This is because the K+ channel plays an important role in determining the repolarization of the cell’s AP.
What is the relative refractory period of an action potential?
The relative refractory period is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before.
What is refractory period of AV node?
The functional refractory period of atrioventricular (AV) transmission has been accepted as a measure of AV nodal refractoriness and has been assumed to be determined solely by conduction of interpolated extrasystoles through the AV node when it is partially refractory.
During which of the following periods of time are the ventricles unable to respond to a stimulus?
During the early part of the QT interval, the ventricles are completely refractory and unable to respond to another electrical impulse. During the latter part of the interval, the ventricles are only partially refractory and may respond to some impulses but not to others. The normal QT interval is <0.44 seconds.
What determines the length of an action potential?
Thus, the amplitude, duration, and shape of the action potential are determined largely by the properties of the excitable membrane and not the amplitude or duration of the stimulus.
What is the typical time interval between the initiation of an impulse by the SA node and the last depolarization of ventricular cells in a healthy heart?
The period of time from the onset of the P wave to the beginning of the QRS complex is termed the PR interval, which normally ranges from 0.12 to 0.20 seconds in duration. This interval represents the time between the onset of atrial depolarization and the onset of ventricular depolarization.
What is the duration of cardiac action potentials?
Cardiac Action Potentials. Cardiac action potentials differ from the APs found in other areas of the body. Typical neural AP duration is around 1ms and those of skeletal muscle are roughly 2-5ms, whereas cardiac action potentials range from 200-400ms.
What is cardiac action potential and how is it investigated?
The cardiac action potential has been investigated elucidated using traditional patch clamp and sharp electrode techniques in single cells and myocardial wedge preparations. However, the main clinical tool used to investigate patients is the 12-lead surface ECG.
What are the three phases of cardiac action potentials?
Cardiac action potentials Phase 0 Influx of sodium ions Phase 1 Inactivation of the sodium-channel Phase 2 Voltage plateau causes the opening of ca Phase 3 Repolarizing of potassium ions
What is the plateau phase of cardiac action potential?
The ST segment, which is the period between the end of the QRS complex and the onset of the T wave, represents the plateau phase of the cardiac action potential.