Name: how the heart sets its own beat
Uploaded: 2025-05-15T09:15:50.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Human Anatomy and Physiology

Transport

Cardiovascular System

Conduction System of the Heart

Autorhythmicity refers to the innate ability of the heart to initiate electrical signals and trigger muscle contractions.
This intrinsic conduction system comprises the pacemaker and specialized conducting cells.
The pacemaker cells are present in the sinoatrial or the SA node and the atrioventricular or the AV node, while the conducting cells are distributed throughout the myocardium.
The SA node pacemaker cells can spontaneously depolarize to trigger an action potential, leading to atrial contraction.
This cardiac action potential reaches the AV node via internodal pathways, pausing momentarily, allowing atrial contraction.
This impulse progresses through the AV bundles or bundle of His into the left and right bundle branches.
Finally, it reaches the Purkinje fibers, which begin ventricular contraction.
While the SA nodes naturally generate cardiac signals at a rate of about 100 contractions per minute, the ANS and hormones can modify the timing and strength of each heartbeat.
At rest, the parasympathetic division of the ANS slows the pacing of the SA node to around 75 contractions per minute, while the sympathetic division can elevate it.

conduction system of the heart

Autorhythmicity is a term that refers to the heart's inherent ability to generate electrical signals and instigate muscle contractions. This self-regulating conduction system within the heart consists of two key components: the pacemaker cells and specialized conducting cells.
The pacemaker cells are located in two primary nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node pacemaker cells can autonomously depolarize, triggering an action potential that leads to the contraction of the atria. This electrical potential then travels to the AV node via specific pathways, pausing briefly to ensure complete atrial contraction before proceeding.
From the AV node, this electrical impulse is transmitted through the AV bundle or the bundle of His, which bifurcates into the left and right bundle branches. Eventually, it reaches the Purkinje fibers, initiating the contraction of the ventricles.
The SA node inherently produces cardiac signals at a rate of roughly 100 contractions per minute. However, the autonomic nervous system (ANS) and various hormones can adjust both the timing and strength of each heartbeat. In a state of rest, the parasympathetic division of the ANS reduces the SA node pacing to approximately 75 contractions per minute. Conversely, the sympathetic division can increase this rate. So, autorhythmicity plays a crucial role in regulating our heartbeat, adapting to the body's needs in different states of activity or rest.

Autorhythmicity refers to the innate ability of the heart to initiate electrical signals and trigger muscle contractions.
This intrinsic conduction system ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

The Heart

KEY TERMS AND CONCEPTS

how the heart sets its own beat

The heart sets its own beat through autorhythmicity, which is its built-in ability to generate electrical signals and start muscle contractions. This process depends on a self-regulating conduction system. It includes pacemaker cells and specialized conducting cells.

Pacemaker cells are found in two main nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node can depolarize on its own. That electrical change starts an action potential that causes the atria to contract.

The signal then travels from the SA node to the AV node through specific pathways. It pauses briefly at the AV node so the atria can finish contracting. After that, the impulse moves through the AV bundle, also called the bundle of His.

The bundle of His splits into the left and right bundle branches. The signal then reaches the Purkinje fibers, which trigger the ventricles to contract. This sequence helps the heart contract in an organized way.

The SA node normally produces cardiac signals at about 100 contractions per minute. The autonomic nervous system and hormones can change both the timing and the strength of each heartbeat. At rest, the parasympathetic division lowers the SA node pacing to about 75 contractions per minute. The sympathetic division can raise the rate when the body needs it.

How the Heart Sets Its Own Beat

overview of the heart

How the Heart Pumps Blood

The heart is a muscular organ in the chest that pumps blood through the body. It works as the main pump of the vascular system. The heart has four chambers. The two atria are on top, and the two ventricles are below. Blood enters the right atrium from the body as deoxygenated blood, which means it has less oxygen. It then moves to the right ventricle. The right ventricle pumps this blood to the lungs for oxygenation. Oxygenated blood returns from the lungs to the left atrium. It then passes to...

location and orientation of the heart

Heart Position, Apex, and Pericardium

The human heart sits in the mediastinum, the middle space of the thorax. It is about the size of a fist and weighs about 250 to 350 grams. The heart lies on the superior surface of the diaphragm and extends obliquely for about 12 to 14 cm. The heart is positioned anterior to the vertebral column and posterior to the sternum. About two-thirds of its mass lies to the left of the midsternal line. The lungs lie on either side of the heart. The broad base of the heart points toward the right...

layers of the heart wall

Heart Wall Layers and Their Roles

The heart wall has three layers: the epicardium, myocardium, and endocardium. Each layer has a different structure and job. Together, they help the heart pump blood through the body. The outermost layer is the epicardium. It is the visceral layer of the serous pericardium. This layer has a thin, transparent mesothelial surface and an inner layer of areolar connective tissue. Fat deposits are also found here, and they increase with age. The myocardium is the thickest layer of the heart wall.

chambers of the heart

Heart Chambers and Blood Flow Pathway

The heart chambers work together to move blood through the body and the lungs. The human heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle. The atria are the upper chambers, and the ventricles are the lower chambers. They are separated by the interatrial septum and the interventricular septum. The outside of the heart also shows clear dividing lines. The coronary sulcus separates the atria from the ventricles. The anterior and posterior...

heart valves

How Heart Valves Prevent Backflow

The heart valves keep blood moving in one direction through the heart. The main valve groups are the atrioventricular, or AV, valves and the semilunar valves. Together, they help stop blood from flowing backward as the heart chambers contract and relax. The AV valves stop blood from moving back into the atria when the ventricles contract. They work with the chordae tendineae, which are tough cord-like strands, and the papillary muscles. When the ventricles relax, the chordae tendineae are...

overview of systemic and pulmonary circulation

overview-of-systemic-and-pulmonary-circulation

Pathway of Blood Through Heart and Lungs

The circulatory system moves blood in two linked routes: pulmonary circulation and systemic circulation. Together, these circuits carry blood between the heart, the lungs, and the rest of the body. Pulmonary circulation comes first in this cycle. In pulmonary circulation, deoxygenated blood is pumped from the right ventricle to the lungs through the pulmonary trunk and pulmonary arteries. In the lungs, the blood picks up oxygen. It then returns to the heart through the pulmonary veins and...

coronary circulation

How the Heart Gets Its Blood

Coronary circulation is the blood supply that keeps the heart muscle alive. The heart does not use the same blood it pumps to feed itself. Instead, it depends on a separate vessel network that delivers oxygen and nutrients to the myocardium, or heart muscle. This is the shortest circulation in the body. Coronary circulation begins at the base of the aorta, where the left and right coronary arteries arise. These arteries wrap around the heart in the coronary sulcus and send blood inward to the...

The heart sets its own beat through autorhythmicity, which is its built-in ability to generate electrical signals and start muscle contractions. This process depends on a self-regulating conduction system. It includes pacemaker cells and specialized conducting cells. Pacemaker cells are found in two main nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node can depolarize on its own. That electrical change starts an action potential that causes the atria to contract. <br...

electrocardiogram

Reading Heart Waves on an ECG

An electrocardiogram, or ECG/EKG, records the heart’s electrical signals during each heartbeat. Electrodes are placed on the arms, legs, and chest. The electrocardiograph then amplifies the signals and creates 12 tracings that show the heart’s electrical activity from different views. A normal ECG has three main waveforms. The P wave shows atrial depolarization, which is the spread of action potentials through the atria. The QRS complex shows rapid ventricular depolarization, and the T wave...

cardiac cycle

Heartbeat Stages and Valve Action

The heartbeat follows a set of stages that move blood through the heart. This process is driven by changes in pressure and by the opening and closing of the heart valves. It includes systole, or contraction, and diastole, or relaxation. The sequence starts in mid-to-late diastole, when the heart is fully relaxed. During this time, blood flows passively from the atria into the ventricles. Atrial systole then begins as the atria contract and push the remaining blood into the ventricles. Next...

correlation between ecg and cardiac cycle

correlation-between-ecg-and-cardiac-cycle

ECG Waves Across the Cardiac Cycle

ECG waves show how the heart’s electrical signals line up with the cardiac cycle. The electrical activity appears before the heart muscle’s mechanical contraction and relaxation. On an electrocardiogram, the main waves help link each electrical event to a specific stage of the heartbeat. A cardiac action potential starts in the SA node, or sinoatrial node, and spreads through the atria and the AV node in about 0.03 seconds. This creates the P wave on the ECG and triggers atrial contraction.

disturbances in heart rhythm

Heart Rhythm Disorders and Emergency Care

Heart rhythm disorders, also called arrhythmias or dysrhythmias, happen when the heart’s conduction system has a defect. They can make the heart beat irregularly, too fast, or too slow. People may notice chest pain, shortness of breath, or fainting. Many things can trigger an arrhythmia. Stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte imbalances are all possible causes. These triggers can disrupt the electrical signals that control the...

heart sounds

Auscultation and Normal Heart Sounds

Auscultation is the process of listening to internal body sounds with a stethoscope. Heart sounds are created by turbulence in blood flow when the heart valves close. These sounds are usually heard best a little away from the valves, where the blood flow spreads the sound. The heart makes four types of sounds, but a stethoscope usually picks up only S1 and S2. S1 is the “lub” sound. It happens when the atrioventricular, or A-V, valves close at the start of ventricular systole. S1 is usually...

cardiac output and stroke volume

How Heart Rate Shapes Cardiac Output

Cardiac output shows how much blood the heart pumps each minute. It is the volume ejected by the left or right ventricle into the aorta or pulmonary trunk. Heart rate and stroke volume work together to set this value. Heart rate is the number of heartbeats per minute, and stroke volume is the amount of blood pumped out with each beat. Cardiac output is found by multiplying heart rate by stroke volume. In an average resting adult male, it is about 5.25 L/min. That estimate uses a heart rate of...

regulation of stroke volume

Stroke Volume: Preload to Afterload

Stroke volume depends on preload, contractility, and afterload. These three factors work together to control how much blood a ventricle ejects with each heartbeat. Understanding them helps explain how the heart keeps blood moving through the circulatory system. Preload is the stretch on the heart before it contracts. It is linked to the Frank-Starling law of the heart, which says that when the heart fills with more blood during diastole, it contracts more forcefully during systole. Preload is...

regulation of heart rates

How the Heart Adjusts Its Beat

Heart rate changes through signals from the autonomic nervous system, hormones, and the heart's own built-in control systems. The autonomic nervous system has two main parts. The sympathetic nervous system raises heart rate, and the parasympathetic nervous system lowers it. The sympathetic nervous system releases norepinephrine and epinephrine. These chemicals act on beta-1 adrenergic receptors in the heart. They increase the rate of depolarization in the sinoatrial (SA) node, which is the...

exercise and cardiac output

How Exercise Strengthens the Heart

Exercise strengthens the heart and improves cardiovascular health. Aerobic exercise is especially effective. The American Heart Association recommends 150 minutes of moderate to intense aerobic exercise each week for a healthy heart. Brisk walking, running, bicycling, cross-country skiing, and swimming are all examples. These activities are best done three to five times per week. During sustained exercise, muscles need more oxygen. The body meets this demand through enough cardiac output and...

imbalances in cardiac output

Congestive Heart Failure Causes and Effects

Congestive heart failure (CHF) happens when the heart becomes an inefficient pump. The heart normally keeps blood leaving the heart and blood returning to it in balance. When that balance is disrupted, blood circulation drops and the body does not get enough flow. CHF can affect the left side of the heart, the right side, or both. Left-side failure can cause pulmonary congestion, which means blood backs up in the lungs. The right side may still send blood to the lungs, but the left side cannot...

development of the heart

Heart Tube Formation and Folding

Heart tube formation and folding shape the early human heart. The process begins in the mesoderm, a middle layer of embryonic tissue, on day 18 or 19 after fertilization. It starts in the cardiogenic area, a group of mesodermal cells at the head end of the embryo. These cells extend into cardiogenic cords and then change into hollow endocardial tubes. As the embryo folds from side to side, the paired tubes move closer together. They join into one primitive heart tube by day 21. By day 22, this...

key terms and concepts

Learn how autorhythmicity lets the heart generate its own electrical signals, from the SA node to Purkinje fibers, and how nerve signals adjust heart rate.

How the Heart Sets Its Own Beat | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

Florida Department of Education

High School

Life Science

SC.912.L.14

SC.912.L.14.37

Overview of the Cardiovascular System

The cardiovascular or circulatory system comprises the blood, the heart, and the blood vessels.
Blood is a specialized fluid comprising cells in a liquid ...

Characteristics and Functions of Blood

Approximately 8% of the body mass comprises whole blood, a specialized connective tissue vital for transportation, regulation, and protection.
The ...

Composition of Blood

Whole blood consists of the blood plasma, a fluid extracellular matrix, and formed elements, including cells and cell fragments.
Blood plasma, which makes ...

Composition of Blood Plasma

Blood plasma is a fluid that contains approximately 92% water and 8% solutes. The solutes include various types of proteins, which constitute about 7% of ...

Overview of Hematopoiesis

Hematopoiesis, or hemopoiesis, is the production of the formed elements in blood from common progenitors, called hematopoietic stem cells, or HSCs.
During ...

Production of Formed Elements

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The HSCs undergo hematopoiesis to produce ...

Role of Hematopoietic Growth Factors

Hematopoietic growth factors are a group of regulatory and signaling molecules that influence the differentiation of hematopoietic stem cells, or HSCs.
...

Erythropoiesis

Factors Affecting Erythropoiesis

The cardiovascular system regulates erythrocyte numbers for optimal oxygen transport. It also prevents erythrocyte over-proliferation, maintaining blood ...

Structure and Function of Erythrocytes

There are 4.2 to 6 million erythrocytes, or red blood cells, per microliter of blood. These small cells are flattened biconcave discs with depressed ...

Hemoglobin

Hemoglobin is a tetrameric globular protein consisting of two alpha and two beta polypeptide chains.
Each of these chains has an iron-containing heme ...

Lifecycle of Erythrocytes

The circulating erythrocytes frequently squeeze through blood capillaries, damaging their plasma membrane due to constant friction.
After about 100 to 120 ...

Disorders of Erythrocytes

Erythrocyte disorders are broadly categorized into anemic and polycythemic conditions.
Anemia develops due to the low oxygen-carrying capacity of the ...

Structure and Function of Leukocytes

A healthy individual has about 4,500 to 11,000 leukocytes or white blood cells per microliter of blood, accounting for about 1% of blood volume.
Unlike ...

Classification of Leukocytes

Leukocytes are classified into two groups based on the presence or absence of cytoplasmic granules. Granular leukocytes, which contain granules, belong to ...

Disorders of Leukocytes

Leukocyte disorders are characterized by either leukopenia, an abnormally low leukocyte count, or leukocytosis, a very high leukocyte number.
Bone marrow ...

Structure and Function of Platelets

The cell fragments known as platelets are disc-shaped, with an average diameter of about 3 &#956;m and a thickness of roughly 1 &#956;m. They play a ...

Introduction to Hemostasis

Hemostasis is a series of rapid, defensive reactions triggered to stop excessive bleeding and promote healing after a vascular injury.
It is a highly ...

Vascular Spasm

The vascular phase, also known as vasospasm, is the initial stage of hemostasis, crucial for preventing excessive bleeding when a blood vessel is injured. ...

Formation of the Platelet Plug

In an injured blood vessel, the platelet phase - which overlaps with the vascular phase - begins about 15-20 seconds after the onset of vascular spasm.
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Coagulation

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extrinsic-and-intrinsic-pathways-of-hemostasis

Extrinsic and Intrinsic Pathways of Hemostasis

The extrinsic and intrinsic pathways of coagulation involve reaction cascades of clotting factors. They merge into the common pathway, eventually forming ...

Clot Retraction and Fibrinolysis

The activated platelets in a blood clot extend projections and interact with other platelets and fibrin fibers.
Within 30 to 60 minutes, the contractile ...

Disorders of Hemostasis

Thromboembolic disorders and bleeding disorders are two types of disruptions in hemostasis.
The thromboembolic disorders are characterized by the ...

The ABO Blood Group

The ABO blood group system is based on the presence of specific antigens or agglutinogens on the red blood cells, or RBCs, and antibodies or agglutinins ...

Rh Blood Group

The Rhesus or Rh antigen is a class of agglutinogen on the red blood cells or RBCs. Its presence or absence categorizes a person as Rh-positive or ...

Blood Typing

The antigens A, B, and Rh on the surface of red blood cells serve as the foundation for blood grouping.
When these antigens come in contact with their ...

Blood Transfusion

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Bone Marrow Sampling and Transplants

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Blood

Content elaboration: Blood is composed of plasma and the formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). The primary functions of blood are transportation, protection and regulation. Plasma, the most abundant component of blood, is the liquid portion that transports dissolved nutrients, waste, hormones, antibodies and proteins throughout the body. Red blood cells carry oxygen used during cellular processes throughout the body. White blood cells identify and protect the body against infectious disease and foreign cells. Platelets bind together when a blood vessel is damaged resulting in blood clot formation. The major ABO blood types, A, B, AB and O, are determined by the presence or absence of antigens on the surface of red blood cells. An additional antigen is present or absent on the surface of red blood cells determining Rh factor. Blood type antibodies are found in plasma. Processes related to blood include the production of blood cells and platelets, and hemostasis. Homeostatic imbalances are explored. These include, but are not limited to, sickle cell anemia, hemophilia, deep vein thrombosis, leukemia and lymphoma. Investigations are used to understand and explain blood in a variety of inquiry and design scenarios that can incorporate evolutionary concepts, scientific reasoning, comparative analysis, communication skills and real-world applications.

Blood

Overview of the Heart

The heart is a hollow muscular organ that pumps blood through the body.
It is cone-shaped and weighs about 250 to 300 grams on average.
The heart is ...

Location and Orientation of the Heart

The heart is located in the mediastinum and spans from the first rib to the diaphragm. It lies anterior to the vertebral column, posterior to the sternum, ...

Layers of the Heart Wall

The heart wall has three layers&#8212;the epicardium, the myocardium, and the endocardium.
The outermost layer, the epicardium, is the visceral layer of ...

Chambers of the Heart

The heart has four chambers&#8212;the right atrium, right ventricle, left atrium, and left ventricle.
Externally, the coronary sulcus separates the atria ...

Heart Valves

The heart valves open and close in response to the pressure gradients created by the contracting heart chambers.
These valves regulate the blood flow by ...

Overview of Systemic and Pulmonary Circulation

The pulmonary and systemic circuits work sequentially to move blood between the heart, lungs, and peripheral tissues.
Pulmonary circulation transports ...

Coronary Circulation

The myocardium has its own network of blood vessels, separate from the systemic and pulmonary circuits, called the coronary circulation.
The left and ...

Electrocardiogram

An electrocardiogram, abbreviated as ECG, or EKG, is a test that captures a record of the heart&#39;s electrical activity.
It is performed by placing ...

Cardiac Cycle

The cardiac cycle comprises the contraction, or systole, and relaxation, or diastole, during one heartbeat.
During atrial systole, cardiac action ...

Correlation between ECG and Cardiac Cycle

The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac ...

Disturbances in Heart Rhythm

Disturbances in the heart rhythm, or arrhythmia, can cause irregular heartbeats.
If the heart rate falls below fifty beats per minute, it is called ...

Heart Sounds

Heart sounds are mainly produced when valve closures cause turbulence in the blood.
These are best heard at chest locations slightly away from the valves ...

Cardiac Output and Stroke Volume

Cardiac output is the blood volume ejected from the ventricles into the blood vessels each minute. It is calculated by multiplying the stroke volume by ...

Regulation of Stroke Volume

The stroke volume, which is the volume of blood ejected by a ventricle with each heartbeat, is regulated by three factors: preload, contractility, and ...

Regulation of Heart Rates

The brain's cardiovascular center activates the ANS based on inputs received from sensory receptors.
For example, proprioceptors in muscles and joints ...

Exercise and Cardiac Output

Physical activity is beneficial for cardiovascular health.
For example, the American Heart Association recommends moderate-intensity aerobic exercises, ...

Imbalances in Cardiac Output

Congestive heart failure, or CHF, can reduce the heart's pumping efficiency.
In CHF, an increase in preload excessively stretches the myocardium, ...

Development of the Heart

Development of the heart starts on the 18th or 19th day post-fertilization from a group of mesodermal cells called the cardiogenic area.
By day 20, these ...

Overview of Blood Vessels

Blood vessels are essential components of the cardiovascular system, serving as conduits for blood flow throughout the body.
There are five main types of ...

Structure of Blood Vessels

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Tunica externa is the outermost layer infiltrated with ...

Measurement of Blood Pressure

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Arteries and Arterioles

Based on their size and function, arteries can be grouped into three types.
The elastic arteries are the largest arteries located close to the heart. They ...

Venous Return

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It is primarily driven by the pressure difference between ...

Capillaries and Their Types

Capillaries are the smallest blood vessels, with a diameter of 8 to 10 &#956;m.
They comprise a single layer of endothelial cells surrounded by a basement ...

Pulse

The pulse is a pressure wave caused by the expansion and recoil of elastic arteries after each systole.
It is a vital sign providing insights into the ...

Capillary Beds

A capillary bed is a network of 10 to 100 capillaries that run between an arteriole and a venule, facilitating microcirculation.
The oxygenated blood ...

Capillary Exchange

Capillary exchange refers to the movement of substances between blood and interstitial fluid.
It occurs through three mechanisms &#8212; diffusion, ...

Cardiovascular System

Content elaboration: The cardiovascular system consists of the heart and blood vessels. The heart is mostly comprised of cardiac muscle which is supplied with oxygenated blood by coronary arteries. The structure of the heart includes four chambers, four valves and major vessels leading to and from the heart. The flow of blood through the heart, pulmonary and systemic circuits should be explored. Blood flows from arteries, to arterioles, to capillaries, to venules, then to veins. In the capillaries, oxygen, nutrients, and chemical messengers diffuse out (leave) and carbon dioxide and other waste products diffuse in (enter). Veins have valves that keep the blood flowing toward the heart. The primary function of the cardiovascular system is the transport of oxygen, carbon dioxide, hormones, nutrients, waste products and chemical messengers. Processes involved in the cardiovascular system include the cardiac cycle and cardiac and conductive pathway which is measured by electrocardiograms and blood pressure. Homeostatic imbalances are explored. These include, but are not limited to, a variety of cardiovascular diseases and structural imperfections of the heart, valves and vessels. Examples include, but are not limited to, myocardial infarction, aneurysm, atherosclerosis, hypertrophic cardiomyopathy, hypo/hypertension and arrhythmias. Investigations are used to understand and explain the cardiovascular system in a variety of inquiry and design scenarios that can incorporate evolutionary concepts, scientific reasoning, comparative analysis, communication skills and real-world applications.

How the Heart Sets Its Own Beat

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