Cardiac Conduction  Autorhythmic: cardiac muscle cells depolarize at regular intervals  Cardiac Conduction system: cardiac cells that are specialized to generate AP’s to control contractions of the heart  Pacemaker: the sinoatrial (SA) node, found in the R atrium starts HB and controls rate of contraction. AP’s from node travel down walls of atrium

Cardiac Conduction  Atrioventricular (AV) node: found by the AV valve, acts as a gateway carrying the AP’s from the SA node to the ventricles  AV bundle: a pathway for the AP’s from the AV node to travel through the septum as it splits into R and L branches toward apex of heart  Purkinje fibers: branches of the AV bundle that travel from the apex upward

Cardiac Rhythm  Sinus rhythm: normal heartbeat /min  Nodal rhythm: caused by SA node damage 40-50/min, AV node still working but ectopic focus working for SA node  If both SA and AV nodes are damaged then ectopic foci keep heart beating at /min body lives but brain dies due to lack of oxygen

Electrocardiogram  Electrocardiogram (ECG or EKG): a visual record of the heart’s electrical activity  Systole: contraction of a heart chamber  Diastole: heart chamber relaxes and fills with blood  P wave: caused by the signal from the SA node as it spreads through the atria depolarizing the walls causing systole

Electrocardiogram  PQ segment: time it takes the signal to travel from the SA to AV node,  QRS complex: caused by the signal traveling through the two ventricles,  QRS interval: atria repolarization and diastole  ST segment: ventricular systole  T wave: the repolarization of the ventricles before diastole

Cardiac Output  Cardiac Output (CO): CO= HR x SV normal CO =5250ml/min so all blood in the body will pass through and return to the heart in about a min  Cardiac reserve: the difference of CO at rest and max CO

Heart Rate  Pulse: the heart rate measured at an artery  Tachycardia: persistent heart rate at rest above 100bpm  Bradycardia: persistent heart rate at rest below 60bpm

Stroke Volume  Preload: the stretch on the myocardium before systole  Contractility: how hard the myocardium can contract for a certain preload  Afterload: the blood pressure in the vessels that resists the blood flow out of heart