BIOL 1344 Lecture 7Outline of Last Lecture I. Cell Polarization and DepolarizationII. Generating Action PotentialA. Sodium/potassium PumpB. mV Levels in Cardiac Muscle CellsIII. Pacemaker Cell Cycle – Generating Action Potential Outline of Current Lecture IV. Path of Action Potential in the HeartV. Cardiac CycleA. Ventricular Filling and EjectionB. Cardiac OutputVI. Control of Heart RateCurrent LectureAction potential starts in the sinoatrial node, also known as SA node, or sinus node. From here ittravels to the atrial muscle which causes atrial contraction then goes to the atrioventricular, or AV node. Then this movement spreads to the myocardial cell which is ventricular and finally results in myocardial cell contraction. This whole cycle is cardiac contraction which is the heart’srhythm. This is the line that is sketched out in an EKG test which should go up and down in a regular rhythm, if the line changes in any way, this can be cause for concern. This line has regular intervals labeled P, Q, R, S, and T at which the line slopes or drops. The behaviors of these intervals can determine different heart conditions. For example, if the P slope repeats frequently before moving on to the next intervals, this is called an atrial flutter or fibrillation which is the most common abnormal heart rhythm. While not necessarily life threatening, it is afaster beating of the heart and can result in shortness of breath and trouble with regular life activities. Cardiac Cycle: the process of ventricular filling1. Isovolumetric relaxation – ventricles expand and all valves close so there is no blood flow2. Passive filling – atrioventricular valves open and ventricles are 80% filled3. Active filling: remaining 20% of blood goes into the ventricles through atrial contractionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The volume of blood in the heart at this point is called End Diastolic Volume (EDV). At this point the ejection phase begins during which blood leaves the ventricles.1. Isovolumetric contraction – ventricles contract and all valves close so there is no blood flow2. Ejection – pulmonary and aortic valves open and blood goes outThe blood volume in the heart at this point is called End Systolic Volume (ESV). There is always some level of blood in the heart, it is never completely empty. The EDV-ESV = stroke volume (SV)per beat for each ventricle. Therefore cardiac output = SV multiplied by the heart rate. For example, 70mL stroke volume X 70 beats/min = 5 L blood/minute.Control of Heart Rate – the human heart is myogenic which means no nerves are necessary to keep the heart beating. Even if all the nerves were cut, the heart would continue beating. There are two types of nerve fibers – sympathetic and parasympathetic. Sympathetic nerve fibers speed the heart rate up by secreting epinephrine and this is called a positive chronotropic effect. These fibers are part of the cardio-accelerator center. If the heart starts beating too fast, sometimes beta blockers are necessary to slow it down. Parasympathetic nerve fibers slow the heart rate down through acetylcholine which is a negative chronotrpic effect. These are part of the cardio-inhibitor center. If the heart rate becomes too slow, epinephrine can be administered to help a failing