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By hyperpolarizing a neuron, an inhibitory stimulus results in a greater negative charge that must be overcome for depolarization to occur. Excitation stimuli, on the other hand, increase the voltage in the neuron, which leads to a neuron that is easier to depolarize than the same neuron in the resting state.
For example, depolarizing from right to left would produce a positive deflection in lead I because the two vectors point in the same direction. In contrast, that same depolarization would produce minimal deflection in V 1 and V 2 because the vectors are perpendicular, and this phenomenon is called isoelectric.
Diagram of membrane potential changes during an action potential. Hyperpolarization is a change in a cell's membrane potential that makes it more negative. Cells typically have a negative resting potential, with neuronal action potentials depolarizing the membrane.
P-wave changes in left and right atrial hypertrophy. Bifid P waves (known as P mitrale) indicate left-atrial abnormality - e.g. dilatation [6] or hypertrophy. [1] If at least three different shaped P waves can be seen in a given ECG lead tracing, this implies that even if one of them arises from the SA node, at least two others are arising ...
Further, the left ventricle has thicker walls than the right because it needs to pump blood to most of the body while the right ventricle fills only the lungs. [ citation needed ] [ 1 ] On the inner walls of the ventricles are irregular muscular columns called trabeculae carneae which cover all of the inner ventricular surfaces except that of ...
The standard model used to understand the cardiac action potential is that of the ventricular myocyte. Outlined below are the five phases of the ventricular myocyte action potential, with reference also to the SAN action potential. Figure 2a: Ventricular action potential (left) and sinoatrial node action potential (right) waveforms.
As diastole ends, the ventricles begin depolarizing and, while ventricular pressure starts to rise owing to contraction, the atrioventricular valves close in order to prevent backflow to the atria. At this stage, which corresponds to the R peak or the QRS complex seen on an ECG , the semilunar valves ( aortic and pulmonary valves) are also closed .
The left posterior fascicle transmits impulses to the papillary muscles, leading to mitral valve closure. As the left posterior fascicle is shorter and broader than the right, impulses reach the papillary muscles just prior to depolarization, and therefore contraction, of the left ventricle myocardium. This allows pre-tensioning of the chordae ...