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The slope of phase 0 on the action potential waveform (see figure 2) represents the maximum rate of voltage change of the cardiac action potential and is known as dV/dt max. In pacemaker cells (e.g. sinoatrial node cells ), however, the increase in membrane voltage is mainly due to activation of L-type calcium channels.
Further down the electrical conducting system of the heart is the Bundle of His. The left and right bundle branches, and the Purkinje fibers, will also produce a spontaneous action potential at a rate of 30–40 beats per minute, so if the SA and AV node both fail to function, these cells can become pacemakers. These cells will be initiating ...
An impulse (action potential) that originates from the SA node at a relative rate of 60–100 bpm is known as a normal sinus rhythm. If SA nodal impulses occur at a rate less than 60 bpm, the heart rhythm is known as sinus bradycardia. If SA nodal impulses occur at a rate exceeding 100 bpm, the consequent rapid heart rate is sinus tachycardia ...
The slope determines the time taken to reach the threshold potential, and thus the timing of the next action potential. [ 2 ] 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 [ 3 ] [ 4 ] ), the pacemaker potential is the ...
The heart is composed of an excitable tissue and an electrical pulse of a certain voltage is needed to "capture" the myocardium to make the heart function. The minimum voltage to achieve this is called the threshold. As this is a probabilistic property, the actual voltage used is higher than the threshold (usually by a 50-100% margin).
A molecule, called adenosine triphosphate (ATP) which is produced by an intracellular structure called a mitochondrion, is then used, as a source of energy, to help move the myosin head, carrying the actin. As a result, the actin slides across the myosin filament shortening the muscle. This is called a power stroke.
Once the pacemaker potential reaches a set value, the threshold potential, it produces an action potential. [2] Other cells within the heart (including the Purkinje fibers [ 11 ] and atrioventricular node ) can also initiate action potentials; however, they do so at a slower rate and therefore, if the SA node is functioning properly, its action ...
Several agents called "heart rate reducing agents" act by specifically inhibiting f-channel function. [3] Ivabradine is the most specific and selective I f inhibitor and the only member of this family that is now marketed for pharmacological treatment of chronic stable angina in patients with normal sinus rhythm who have a contraindication or ...