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Purkinje fibers also have the ability of firing at a rate of 20–40 beats per minute if upstream conduction or pacemaking ability is compromised. [9] In contrast, the SA node in normal state can fire at 60-100 beats per minute. [9] In short, they generate action potentials, but at a slower rate than the sinoatrial node. [9]
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 ...
The Purkinje fibers have a fast inherent conduction rate, and the electrical impulse reaches all of the ventricular muscle cells in about 75 ms. Since the electrical stimulus begins at the apex, the contraction also begins at the apex and travels toward the base of the heart, similar to squeezing a tube of toothpaste from the bottom.
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 impulse then spreads through both ventricles via the bundle of His and the Purkinje fibers causing a synchronized contraction of the heart muscle and, thus, the pulse. [citation needed] In adults, the normal resting heart rate ranges from 60 to 90 beats per minute. The resting heart rate in children is much faster.
Parallel fibers pass orthogonally through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers [6] forming a Granule-cell-Purkinje-cell synapse with a single Purkinje cell. Each adult Purkinje cell receives approximately 500 climbing fiber synapses, all originating from a single climbing fiber from the inferior olive. [ 7 ]
According to V. Gorshkov-Cantacuzene: "The U wave is the momentum carried by the blood in the coronary arteries and blood vessels". [4] [5] [6]The resistivity of stationary blood is expressed as () = | (+), where is a coefficient, and is the hematocrit; at that time, as during acceleration of the blood flow occurs a sharp decrease in the longitudinal resistance with small relaxation times.
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 potentials usually override those that would be produced by other tissues. [12]