Experimental beating heart transplants depend upon cardiac muscle's ability to contract on its own. This new technique circulates blood and allows the heart to beat while in transit. Contrast this to typical heart transplants, where a picnic cooler filled with ice is used to preserve and transport the heart. The ability of cardiac muscle to beat on its own is dependent on the electrical impulses that are generated in the sinoatrial node. The heart has a built-in system that is responsible for generating impulses that are sequentially transmitted through the heart. This system, made up of cardiac pacemaker cells, is called the intrinsic conduction system, colored yellow in the drawing. This video will describe the components of the intrinsic conduction system; define electrocardiogram and what it measures; correlate the electrical events in the heart with the waves of an ECG tracing; define segments and intervals; and enable you to predict the effect of various scenarios on the R to R interval. The structures of the intrinsic conduction system include the sinoatrial node, the atrioventricular node, the atrioventricular bundle, the left and right bundle branches, and the subendocardial conducting network (also known as Purkinje fibers). The conduction of impulses through the heart generates electrical currents that spread and can be detected on the body's surface. A graphic recording of these electrical changes is called an electrocardiogram (abbreviated ECG or EKG). The ECG is a recording of voltage on the vertical axis against time on the horizontal axis. Shown here is a normal ECG with normal sinus rhythm. The waves or deflections on the tracing correlate to electrical changes in the heart, either depolarization or repolarization. The excitation of the heart begins with an impulse generated in the sinoatrial (or SA) node, located in the right atrium. The SA node, also known as the pacemaker, initiates and sets the rate of depolarization. The deflection of the P wave on the ECG represents the beginning of depolarization of the atria. The P wave as a whole is caused by atrial depolarization. From the SA node, impulses spread through the cardiac muscle of the atria via gap junctions and stimulate the atria to contract. So under normal conditions, the atria should contract shortly after the P wave. Note that an ECG does not detect contraction; it is inferred to occur following depolarization. The impulses travel from the SA node to the atrioventricular (or AV) node via the internodal pathway. The AV node is located in the lower interatrial septum in the right atrium. At the atrioventricular node, the impulse is slightly delayed, allowing the atria to completely contract. After the delay, the impulses travel from the AV node to the AV bundle located in the interventricular septum, then through the left and right bundle branches also located in the interventricular septum. Although the atria and ventricles are adjacent to each other, they are not connected by gap junctions. Consequently, the AV bundle is the only electrical connection between them. Let's check your understanding. Which of the following structures primarily controls the rate of heartbeats: the SA node, AV node, AV bundle, or bundle branches? >> The SA node controls the intrinsic heartbeat rate in its role as the pacemaker of the heart. The impulses travel from the bundle branches to the subendocardial conducting network, also known as Purkinje fibers, which carry the impulses to the apex of the heart and through the walls of the ventricles. The QRS complex represents the depolarization of the ventricles. There is no visible wave representing atrial repolarization because it is small in amplitude and is hidden by the QRS complex. Usually the ventricles will contract shortly after the S deflection. The ventricles are uniformly depolarized during the S-T segment. Ventricular repolarization begins at the apex and is represented by the T wave. The ventricular repolarization progresses superiorly. Let's check your understanding. Which of the following is not matched correctly? P wave and atrial depolarization; QRS complex and ventricular depolarization; or T wave and atrial repolarization? >> The T wave corresponds to ventricular repolarization. Repolarization of the atria is hidden by the large QRS complex. Abnormalities of the waves and changes in the timing of the deflections are useful in detecting cardiac abnormalities and problems with the conduction system of the heart. For example, an enlarged R wave could indicate that the ventricles are enlarged. In addition to measuring the height and duration of a wave, we also analyze segments and intervals. A segment is a region between two waves. For example, the S-T segment starts at the end of the S deflection and ends at the beginning of the T wave. An interval is a region that includes a segment and one or more waves. Two important intervals that are measured include the P to R and the Q-T intervals. The P to R interval starts at the beginning of atrial depolarization and goes to the start of ventricular depolarization. The Q-T interval is the period from the start of ventricular depolarization through ventricular repolarization. Let's check your understanding. Given the description "the end of the T wave to the start of the P wave," would this be a segment or an interval? >> It is a segment, because it is a region between two waves. There are no waves between the T wave and the P wave. Heart rate is usually expressed in beats per minute, or bpm. The R to R interval provides a convenient way to calculate heart rate, since the distance between R peaks corresponds to one heartbeat. Your instructor will explain how to convert the R to R interval into a heart rate. In this lab, you will record electrical activity of the heart of a subject lying down, sitting up, and after exercise. You will use electrocardiograms to determine heart rate. Think about how you expect heart rate to change with these scenarios.
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
- Levels of Organization13m
- Variation in Anatomy & Physiology12m
- Introduction to Organ Systems27m
- Homeostasis9m
- Feedback Loops11m
- Feedback Loops: Negative Feedback19m
- Feedback Loops: Positive Feedback11m
- Anatomical Position7m
- Introduction to Directional Terms3m
- Directional Terms: Up and Down9m
- Directional Terms: Front and Back6m
- Directional Terms: Body Sides12m
- Directional Terms: Limbs6m
- Directional Terms: Depth Within the Body4m
- Introduction to Anatomical Terms for Body Regions3m
- Anatomical Terms for the Head and Neck8m
- Anatomical Terms for the Front of the Trunk8m
- Anatomical Terms for the Back9m
- Anatomical Terms for the Arm and Hand9m
- Anatomical Terms for the Leg and Foot15m
- Review- Using Anatomical Terms and Directions12m
- Abdominopelvic Quadrants and Regions19m
- Anatomical Planes & Sections17m
- Organization of the Body: Body Cavities13m
- Organization of the Body: Serous Membranes14m
- Organization of the Body: Serous Membrane Locations8m
- Organization of the Body: Thoracic Cavity8m
- Organization of the Body: Abdominopelvic Cavity12m
- 2. Cell Chemistry & Cell Components12h 37m
- Atoms- Smallest Unit of Matter57m
- Isotopes39m
- Introduction to Chemical Bonding19m
- Covalent Bonds40m
- Noncovalent Bonds5m
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- Introduction to Water7m
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- Prokaryotic & Eukaryotic Cells26m
- Introduction to Eukaryotic Organelles16m
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- Endosymbiotic Theory10m
- Introduction to the Cytoskeleton10m
- Cell Junctions8m
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- Types of Membrane Proteins7m
- Concentration Gradients and Diffusion9m
- Introduction to Membrane Transport14m
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- Osmosis33m
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- Introduction to Cellular Respiration22m
- Types of Phosphorylation11m
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- Krebs Cycle16m
- Electron Transport Chain14m
- Chemiosmosis7m
- Review of Aerobic Cellular Respiration19m
- Fermentation & Anaerobic Respiration23m
- Introduction to Cell Division22m
- Organization of DNA in the Cell17m
- Introduction to the Cell Cycle7m
- Interphase18m
- Phases of Mitosis48m
- Cytokinesis16m
- Cell Cycle Regulation18m
- Review of the Cell Cycle7m
- Cancer13m
- Introduction to DNA Replication22m
- DNA Repair7m
- Central Dogma7m
- Introduction to Transcription20m
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- Genetic Code25m
- Introduction to Translation30m
- Steps of Translation23m
- Post-Translational Modification6m
- 4. Tissues & Histology10h 3m
- Introduction to Tissues & Histology16m
- Introduction to Epithelial Tissue24m
- Characteristics of Epithelial Tissue37m
- Structural Naming of Epithelial Tissue19m
- Simple Epithelial Tissues1h 2m
- Stratified Epithelial Tissues55m
- Identifying Types of Epithelial Tissue32m
- Glandular Epithelial Tissue26m
- Introduction to Connective Tissue36m
- Classes of Connective Tissue8m
- Introduction to Connective Tissue Proper40m
- Connective Tissue Proper: Loose Connective Tissue56m
- Connective Tissue Proper: Dense Connective Tissue49m
- Specialized Connective Tissue: Cartilage44m
- Specialized Connective Tissue: Bone12m
- Specialized Connective Tissue: Blood9m
- Introduction to Muscle Tissue7m
- Types of Muscle Tissue45m
- Introduction to Nervous Tissue8m
- Nervous Tissue: The Neuron8m
- 5. Integumentary System2h 20m
- 6. Bones & Skeletal Tissue2h 16m
- An Introduction to Bone and Skeletal Tissue18m
- Gross Anatomy of Bone: Compact and Spongy Bone7m
- Gross Anatomy of Bone: Periosteum and Endosteum11m
- Gross Anatomy of Bone: Bone Marrow8m
- Gross Anatomy of Bone: Short, Flat, and Irregular Bones5m
- Gross Anatomy of Bones - Structure of a Long Bone23m
- Microscopic Anatomy of Bones - Bone Matrix9m
- Microscopic Anatomy of Bones - Bone Cells25m
- Microscopic Anatomy of Bones - The Osteon17m
- Microscopic Anatomy of Bones - Trabeculae9m
- 7. The Skeletal System2h 35m
- 8. Joints2h 17m
- 9. Muscle Tissue2h 33m
- 10. Muscles1h 11m
- 11. Nervous Tissue and Nervous System1h 35m
- 12. The Central Nervous System1h 6m
- 13. The Peripheral Nervous System1h 26m
- Introduction to the Peripheral Nervous System5m
- Organization of Sensory Pathways16m
- Introduction to Sensory Receptors5m
- Sensory Receptor Classification by Modality6m
- Sensory Receptor Classification by Location8m
- Proprioceptors7m
- Adaptation of Sensory Receptors8m
- Introduction to Reflex Arcs13m
- Reflex Arcs15m
- 14. The Autonomic Nervous System1h 38m
- 15. The Special Senses2h 41m
- 16. The Endocrine System2h 48m
- 17. The Blood1h 22m
- 18. The Heart1h 42m
- 19. The Blood Vessels3h 35m
- 20. The Lymphatic System3h 16m
- 21. The Immune System14h 37m
- Introduction to the Immune System10m
- Introduction to Innate Immunity17m
- Introduction to First-Line Defenses5m
- Physical Barriers in First-Line Defenses: Skin13m
- Physical Barriers in First-Line Defenses: Mucous Membrane9m
- First-Line Defenses: Chemical Barriers24m
- First-Line Defenses: Normal Microbiota7m
- Introduction to Cells of the Immune System15m
- Cells of the Immune System: Granulocytes28m
- Cells of the Immune System: Agranulocytes26m
- Introduction to Cell Communication5m
- Cell Communication: Surface Receptors & Adhesion Molecules16m
- Cell Communication: Cytokines27m
- Pattern Recognition Receptors (PRRs)48m
- Introduction to the Complement System24m
- Activation Pathways of the Complement System23m
- Effects of the Complement System23m
- Review of the Complement System13m
- Phagocytosis17m
- Introduction to Inflammation18m
- Steps of the Inflammatory Response28m
- Fever8m
- Interferon Response25m
- Review Map of Innate Immunity
- Introduction to Adaptive Immunity32m
- Antigens12m
- Introduction to T Lymphocytes38m
- Major Histocompatibility Complex Molecules20m
- Activation of T Lymphocytes21m
- Functions of T Lymphocytes25m
- Review of Cytotoxic vs Helper T Cells13m
- Introduction to B Lymphocytes27m
- Antibodies14m
- Classes of Antibodies35m
- Outcomes of Antibody Binding to Antigen15m
- T Dependent & T Independent Antigens21m
- Clonal Selection20m
- Antibody Class Switching17m
- Affinity Maturation14m
- Primary and Secondary Response of Adaptive Immunity21m
- Immune Tolerance28m
- Regulatory T Cells10m
- Natural Killer Cells16m
- Review of Adaptive Immunity25m
- 22. The Respiratory System3h 20m
- 23. The Digestive System2h 5m
- 24. Metabolism and Nutrition4h 0m
- Essential Amino Acids5m
- Lipid Vitamins19m
- Cellular Respiration: Redox Reactions15m
- Introduction to Cellular Respiration22m
- Cellular Respiration: Types of Phosphorylation14m
- Cellular Respiration: Glycolysis19m
- Cellular Respiration: Pyruvate Oxidation8m
- Cellular Respiration: Krebs Cycle16m
- Cellular Respiration: Electron Transport Chain14m
- Cellular Respiration: Chemiosmosis7m
- Review of Aerobic Cellular Respiration18m
- Fermentation & Anaerobic Respiration23m
- Gluconeogenesis16m
- Fatty Acid Oxidation20m
- Amino Acid Oxidation17m
- 25. The Urinary System2h 39m
- 26. Fluid and Electrolyte Balance, Acid Base Balance Coming soon
- 27. The Reproductive System2h 5m
- 28. Human Development1h 21m
- 29. Heredity Coming soon
18. The Heart
Electrocardiogram (ECG)
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