Conduction of electrical activity in the heart
Burt B. Hamrell in Cardiovascular Physiology, 2018
The sinoatrial (SA) node is in the right atrium at its juncture with the superior vena cava (Figure 6.1). The SA node is the normal pacemaker of the heart (self-study module Cardiac Action Potentials, Part 2: Nodal and Conduction System Myocytes). As noted above, electrical activity begins here, initiates each heartbeat, and then spreads throughout the atria.
Circarhythms
Sue Binkley in Biological Clocks, 2020
An ultradian rhythm, or high frequency rhythm, has a period shorter than 24 hours, or a frequency greater than one cycle in 20 hours. This would seem to include circatidal rhythms, and bimodal patterns of activity in house sparrows, but they are usually treated as a separate case. The “ultra” refers to frequency, not period length. There are 24 eyeblinks/minute in the human. Compound action potentials (CAPs) have up to 300 impulses/hour in the optic nerve of the Aplysia eye. 12–15 respirations take place every minute and there are about 70 heartbeats/minute in the human. Erections take place every 90 minutes in sleeping men. The pacemaker for the heartbeat resides in is in the heart’s sinoatrial node. The pacemakers signals are transmitted electrically to other parts of the heart. Pieces of hearts are capable of beating when isolated in vitro, but the fastest rate is in the sino-atrial node. The signal from the fast beating node drives the rest of the heart. The heart has a pacemaker, a driving oscillator, and its beat might be considered to freerun. However, there is not an environmental signal that entrains the heartbeat. In the laboratory, or with an electronic pacemaker, the heartbeat can be driven experimentally, and shows the phenomenon of frequency demultiplication. Hearts do not exhibit temperature compensation, the turtle heart rate speeds up as temperature increases, and it slows down when the temperature decreases. Signals transmitted to the heart via the vagus nerve slow it down. A transplanted heart is dependent upon its own pacemaker. Siberian hamsters (Phodopus sungorus) exhibited a circadian rhythm of wheel running activity in constant light or dark.
The patient with acute cardiovascular problems
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
The sinoatrial (SA) node is the pacemaker of the heart and can spontaneously become activated (depolarise) at a fixed rate. This inbuilt heartrate is around 100 beats per minute and is referred to as the rate of automaticity. Each cell of the cardiac conduction system has its own rate of automaticity, but the further down in the conduction system the cell is, the slower its rate of automaticity. In order for the heart rate to be increased in times of need and for it to slow down at times of rest, the SA node is controlled externally by the sympathetic and para-sympathetic branches of the autonomic nervous system. The sympathetic nervous system has an excitatory effect on the heart, making it beat faster during exercise, stress, pain or increased metabolic need. The SA node’s rate of automaticity is slightly too fast for normal resting activity or sleeping. Therefore, the SA node is constantly being slowed down, according to the metabolic requirements, via the vagus nerve of the parasympathetic nervous system. So, despite the intrinsic rate of automaticity of the SA node being 100 beats per minute, the heart rate that we accept as being normal (60–100) is actually maintained mostly by the autonomic nervous system. Once the SA node depolarises, the wave of depolarisation spreads across the atria via internodal pathways. These ensure that the atria both depolarise at the same time and that the contraction of the atria occurs in a downward motion (allowing the blood to be pushed down into the ventricles).
Potassium channels in the sinoatrial node and their role in heart rate control
Published in Channels, 2018
Qadeer Aziz, Yiwen Li, Andrew Tinker
ABSTRACT Potassium currents determine the resting membrane potential and govern repolarisation in cardiac myocytes. Here, we review the various currents in the sinoatrial node focussing on their molecular and cellular properties and their role in pacemaking and heart rate control. We also describe how our recent finding of a novel ATP-sensitive potassium channel population in these cells fits into this picture.
Biochemical Processes in Cardiac Function
Published in Hospital Practice, 1970
When the pacemaking impulse is released from the sinoatrial node a series of events is set in motion involving depolarization within the myocardial cell, the diffusion of calcium to the sarcomere, the linkage of thick and thin filaments in the sarcomere, and cardiac contraction. The specific biochemical interactions in this sequence are described in this second article of a symposium on cardiac failure.
Detecting spatial susceptibility to cardiac toxicity of radiation therapy for lung cancer
Published in IISE Transactions on Healthcare Systems Engineering, 2020
Xiaonan Liu, Mirek Fatyga, Steven E. Schild, Jing Li
Radiation therapy (RT) is a commonly used approach for treating lung cancer. Because the lungs are close to the heart, radiation dose may inevitably spill to the heart, causing heart damage and diminishing treatment outcomes. There is an urgent need to better understand how treatment outcomes are affected by radiation dose spilled to the heart in order to optimize RT planning. However, despite the fact that dose distribution on the heart is 3-D, most existing research collapses the 3-D dose map into a 1-D histogram to be linked with outcomes. This ignores the spatial information. We propose a novel method that automatically searches for subregions of the heart that are susceptible to radiation toxicity, called Toxicity-Susceptible Subregions (TSSs), based on the 3-D dose distribution. We apply the proposed method to a real-world dataset and find TSSs that harbor the sinoatrial node of the electronic conduction system of the heart. Damage of the sinoatrial node by radiation toxicity disrupts the crucial function of the heart, leading to shortening of the overall survival. Our finding suggests that protective strategies may be developed to spare the TSSs, and thus helping RT planning achieve optimal results in treating lung cancer patients.
Related Knowledge Centers
- Cardiac Muscle
- Heart
- Sinus Rhythm
- Right Atrium
- Superior Vena Cava
- Action Potential