BIOLOGY 20 Lecture Notes - Lecture 24: Artificial Cardiac Pacemaker, Calcium Atpase, Cardiac Action Potential
Document Summary
Sa node fires spontaneously 70 times per minute at rest. Av node fires 40-50 times per minute. If both nodes are suppressed fibres in ventricles by themselves fire only 20-40 times per minute. Artificial pacemaker needed if pace is too slow. Extra beats forming at other sites are called ectopic pacemakers (caffeine and nicotine increase activity) Sa node setting pace since is the fastest. In 50 msec excitation spreads through both atria and down to av node. 100 msec delay at av node due to smaller diameter fibres allows atria to fully contract filling ventricles before ventricles contract in 50 msec excitation spreads through both ventricles simultaneously. This means that chemicals or ions cause electrical signal called an action potential the cardiac action potential is a brief change in voltage across the cell membrane of heart cells. This is caused by the movement of ions between the inside and outside of the cell, through proteins called ion channels.
