Cardiac conduction

Conduction of action potential through the heart:<img alt="2 step 2 3 4 5 6 7 8 9 10 elapsed time (ms) O 30 150 175 225 event sinoatrial node fires an action potential signal spreads across the atrial surfaces signal reaches the atrioventricular node atria begin to contract —100 ms delay at the atrioventricular node signal travels along the interventricular septum within the atrioventricular bundle, down the bundle branches to the Purkinje fibres and on to the moderator band in the right ventricle signal reaches the papillary muscles of the right ventricle Purkinje fibres distribute signal to ventricular myocardium, where it spreads through the muscle cells. atrial contraction ends, ventricular contraction begins 1 6 9 10 " src="https://knowt-user-attachments.s3.amazonaws.com/fc8e402c-c30a-4404-90b9-fcc7941263b9.png" /> Gap junctions:<ul><li>Cells that conduct electrical signals through the heart are connected end-to-end by structures known as intercalated disks, which contain desmosomes that hold the cells together.</li><li>Gap junctions are found near the desmosomes. They are channels formed between the cells that connect the cytoplasm of the two cells.</li><li>The membrane of each cell contains a protein, known as a hemi-channnel, and together they form the gap junction channel connecting the cells- they provide a pathway for ions and small molecules to move directly between the cells.</li></ul> Conduction Via gap junctions:<ul><li>An action potential, initiated spontaneously in a cell in the sinoatrial node , propagates to neighboring cells via gap junctions.</li><li>Conducting pathways in the heart are formed by strings of cells, connected by gap junctions, that convey the signal all the way from the sinoatrial node to the atrio ventricular node and onwards to muscle cells, where the action potential initiates contraction in a process called excitation-contraction coupling.</li></ul> Conduction delay at Atrioventricular node:<ul><li>Thus, a slow (Ca2+-dependent) action potential in a sino-atrial node cell will trigger a fast (Na+-dependent) action potential in an adjacent cell of the internodal tract.</li><li>When the signal reaches the atrio-ventricular node it activates a slow (Ca2+-dependent) action potential</li><li> It therefore takes around 30 ms for excitation to spread from the sino-atrial node to the atrio-ventricular node, but over 100 ms to pass through the atrio ventricular node and excite cells in the Bundle of His.</li><li>Action potentials in the conduction pathways are of the fast type, the signal is transmitted rapidly (~25ms) from the atrio-ventricular node to ventricular muscle.</li><li>The delay at the atrio ventricular node is important, because it allows time for the atria to finish contracting and pushing blood into the ventricles, before the ventricles start to contract</li></ul> From <<a href="https://softchalkcloud.com/lesson/files/5nbC1YSWT9AJmj/EBL_Cardiac_Conduction4.html">https://softchalkcloud.com/lesson/files/5nbC1YSWT9AJmj/EBL_Cardiac_Conduction4.html</a>> <ul><li> </li></ul>