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An action potential occurs when the membrane potential of a specific cell rapidly ... Anatomy of a neuron ... function by blocking the action potential.
The action potential travels from one location in the cell to another, but ion flow across the membrane occurs only at the nodes of Ranvier. As a result, the action potential signal jumps along the axon, from node to node, rather than propagating smoothly, as they do in axons that lack a myelin sheath.
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.
Once this initial action potential is initiated, principally at the axon hillock, it propagates down the length of the axon. Under normal conditions, the action potential would attenuate very quickly due to the porous nature of the cell membrane. To ensure faster and more efficient propagation of action potentials, the axon is myelinated ...
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 ...
T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
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 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 action potentials and contraction at a much lower rate than the primary or ...