Learning Module 1: Cardiac Physiology Clark J. Cotton

What is Your Heart Rate? To take your pulse, place your fingers on your wrist and count heart beats. Alternatively, place your fingers over your neck and count beats. Your pulse is the number of beats in 15 seconds multiplied by 4.

What is a Heart? The heart is composed of contractile muscle, similar to our skeletal muscle. The heart acts as a pump for our bodies’ blood supply. –Blood is pumped to the lungs via the right ventricle to pick up oxygen. –Blood is pumped to the tissue via the left ventricle to distribute oxygen throughout the body.

Basic Heart Anatomy Heart consists of 4 chambers (2 atria & 2 ventricles). Atria are smaller than ventricles, left ventricle bigger than right ventricle. Blood flows in the following order: 1. Right atria 2. Right ventricle 3. Lungs 4. Left atria 5. Left ventricle 6. Rest of Body

What is an Action Potential? Normally, our cells maintain a membrane potential of -55mV. During an action potential, the membrane potential quickly reaches +5mV for a short time. The large spike in membrane potential is due to an influx of positive Na + and Ca 2+ ions.

What Causes a Heart Contraction? There are several areas of the heart that rhythmically fire action potentials generating a wave of electrical energy. This electrical signal is what causes the heart muscles to contract. The S-A node depolarizes at the fastest rate and is therefore the pacemaker for the heart. The rest of the nodes transfer the electrical signal of the SA-node to the other chambers of the heart, stimulating them to contract in turn.

Electrocardiograms (ECGs) Because a large number of cells in the heart rhythmically depolarize, with each contraction, we can record the electrical changes on our body surface. This electrical trace is known as an electrocardiogram.

Electrocardiogram and Heart Rate 1.The SA-node is the first part of the heart to show electrical activity. ECGHeart

Electrocardiogram and Heart Rate 2.Shortly after the SA-node fires, both atria of the heart depolarize (P-wave) followed closely by atrial contraction. ECGHeart

Electrocardiogram and Heart Rate 3.There is a brief pause, and then the AV-node, Bundle of HIS, and Purkinje fibers fire in succession (QRS complex). ECGHeart

Electrocardiogram and Heart Rate 3.There is a brief pause, and then the AV-node, Bundle of HIS, and Purkinje fibers fire in succession (QRS complex). ECGHeart

Electrocardiogram and Heart Rate 3.There is a brief pause, and then the AV-node, Bundle of HIS, and Purkinje fibers fire in succession (QRS complex). ECGHeart

Electrocardiogram and Heart Rate 3.There is a brief pause, and then the AV-node, Bundle of HIS, and Purkinje fibers fire in succession (QRS complex). ECGHeart

Electrocardiogram and Heart Rate 4.Following Ventricular depolarization, the ventricles contract and repolarization (T-wave) occurs. ECGHeart

How Does the Electrical Signal Travel Throughout the Heart? The electrical signal from pacemaker cells spreads to nearby cells via gap junctions. Gap junctions are channels that are shared by two adjacent cell membranes. When one heart cell fires an electrical signal, the signal quickly spreads to neighboring cells.

Concept Maps Concept maps are a great way to organize complex material in an easy to understand manner. For example, consider the concept of a farm. To describe a farm, you might use the following terms: Farm, Farmer, Banker, Hired Help, Livestock, Land, Machinery, Crops, Manure. A concept map provides a useful framework in which to visualize these terms.

Concept Maps Concept maps are a great way to organize complex material in an easy to understand manner. For example, consider the concept of a farm. To describe a farm, you might use the following terms: Farm, Farmer, Banker, Hired Help, Livestock, Land, Machinery, Crops, Manure. A concept map provides a useful framework in which to visualize these terms.

Cardiac Physiology Concept Map Construct a concept map of cardiac physiology using the following terms: Atria, Ventricles, gap junctions, action potentials, p-waves, QRS complex, t- wave, arteries, veins, systole, diastole, pacemaker, SA-node, AV-node, Bundle of HIS, Purkinje fibers, electrocardiogram.