Trystan Casey
The human heart is a pump made of muscle tissue. Like all muscles, it requires energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its chambers. This system is made up of nodes, cells, and signals that work together to control the heartbeat. The sinus node, a small mass of specialized tissue located in the upper right chamber of the heart, generates an electrical stimulus that travels through the heart, causing it to contract and pump blood. This electrical conduction system ensures a steady heart rate and adjusts it according to the body's needs.
| Characteristics | Values |
|---|---|
| What is the heart's electrical system? | The heart's electrical system is a network of nodes, cells, and signals that controls the heartbeat. |
| What is the heart's electrical signal? | An electrical signal is generated by the heart's sinus node, a small mass of specialized tissue located in the right upper chamber of the heart. |
| How does the electrical signal travel through the heart? | The electrical signal travels through the conduction pathway of the heart, starting at the sinus node and spreading across the right and left atria, causing them to contract and pump blood into the ventricles. |
| What is the role of the atrioventricular (AV) node? | The AV node is located in the middle of the heart, between the atria and ventricles. It receives the electrical signal from the sinus node and delays it for a short period before sending it to the ventricles. |
| What is the role of the bundle of His? | The bundle of His is a branch of nerve cells that extends from the AV node and carries the electrical signal to the Purkinje fibers, which then transmit the signal to the right and left ventricles. |
| What is the role of the Purkinje fibers? | The Purkinje fibers are specialized nerve cells that transmit electrical signals very quickly to the right and left ventricles, causing them to contract and pump blood to the body and lungs. |
| What happens during atrial depolarization? | Atrial depolarization occurs when the electrical impulse spreads across the atria, causing them to contract and push blood into the ventricles. |
| What is the normal heart rate? | Under normal conditions, the heart beats 60 to 100 times per minute in adults and 60 to 190 times per minute in children, depending on age and activity level. |
| What is the impact of heart block? | Heart block is a conduction disorder where electrical signals are unable to move from the atria to the ventricles. This can cause symptoms such as fatigue, dizziness, and fainting. |
| How is the electrical system visualized? | The movement of electrical signals across the heart is traced on an electrocardiogram (EKG) and allows for the assessment of irregularities in the heart's electrical system. |
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What You'll Learn
The sinus node: the heart's pacemaker
The heart is a pump made of muscle tissue. As with all muscles, it requires a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its chambers. This electrical conduction system is made up of nodes, cells, and signals that control the heartbeat.
The sinus node (also called the sinoatrial node, or SA node) is a small mass of specialized tissue located in the right upper chamber (atria) of the heart. It is the heart's natural pacemaker. The SA node is a crescent-like cluster of myocytes (specialized cardiac muscle cells) with pacemaker activity. These cells can spontaneously generate electrical impulses that set the rhythm and rate of the heart.
The SA node is located at the junction of the crista terminalis in the upper wall of the right atrium and the opening of the superior vena cava. The superior vena cava is a large vein that brings oxygen-poor blood from the body to the heart. The SA node is approximately 15 mm long, 3 mm wide, and 1 mm thick.
The sinus node continuously generates electrical impulses, 60 to 100 times per minute under normal conditions. These impulses travel through the conduction pathway of the heart, causing the heart to contract and pump blood through the body. The rate of action potentials produced (and therefore the heart rate) is influenced by the autonomic nervous system, which controls how quickly or slowly the SA node sends electrical signals.
If the SA node is not functioning properly, the lower segments of the conduction system act as a backup pacemaker. Sinus node dysfunction, or sick sinus syndrome, can cause the heart's rhythm to become abnormal, typically resulting in a slow heart rate. This can be treated with the implantation of a permanent pacemaker, a medical device that regulates the heartbeat.
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Electrical signals and the cardiac conduction system
The heart is a pump made up of muscle tissue. Like all muscles, it requires a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart. This electrical conduction system is also known as the cardiac conduction system.
The cardiac conduction system is a network of nodes, cells and signals that controls the heartbeat. Each time the heart beats, electrical signals travel through the heart, causing different parts of it to expand and contract. These actions regulate blood flow through the heart and body. The conduction system contains specialised cells and nodes that control the heartbeat. The main parts of the system are the SA node, AV node, bundle of His, bundle branches, and Purkinje fibres.
The SA node (sinoatrial node) is the heart's natural pacemaker. It sends the electrical impulses that start the heartbeat. The SA node is located in the upper part of the heart's right atrium, near the superior vena cava, a large vein that brings oxygen-poor blood from the body to the heart. The autonomic nervous system controls how quickly or slowly the SA node sends electrical signals. When the SA node isn't working well, the lower segments of the conduction system act as backup pacemaker cells.
The electrical impulse travels from the SA node to the AV node (atrioventricular node). The AV node slows down the impulses for a very short period, then continues them down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways, called bundle branches, to stimulate the right and left ventricles. The bundle branches send electrical signals through the Purkinje fibres to the ventricles.
The cardiac conduction system is essential for maintaining a steady heart rate and adjusting it according to the body's needs. However, several conditions can affect the heart's electrical system, causing issues with the heart's rhythm, such as arrhythmia, bundle branch block, and heart block.
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Electrocardiograms (EKGs) and how they work
The heart, a pump made up of muscle tissue, requires a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its various chambers. This electrical conduction system is made up of nodes, cells, and signals that control the heartbeat. The sinus node (also called the sinoatrial node, or SA node), a small mass of specialized tissue located in the upper right chamber (atria) of the heart, generates an electrical stimulus 60 to 100 times per minute under normal conditions. This electrical impulse causes the heart to contract, pushing blood around the body.
An electrocardiogram (EKG) is a diagnostic test that a healthcare professional uses to measure the electrical activity of a person's heart. EKG is the abbreviation from the German spelling of electrocardiogram (elektrokardiogramm). An EKG is used to look for certain issues with a person's heart rhythm and can be used to detect heart attacks that have already happened, or silent heart attacks. The test is short, painless, and common, and can be performed in a doctor's office, outpatient clinic, or hospital. During the test, electrodes (sticky patches with metal conductors that transmit electrical current) are attached to the patient's chest, arms, or legs. These electrodes are connected to a computer, which records the heart's electrical activity.
As the electrical impulse moves through the heart, it generates a "P" wave on the EKG, indicated by a solid red line. As the wave of electricity reaches the AV disc, a layer of fibrous tissue that separates the atria and ventricles, it is stopped, except in the AV node. When the electrical signal travels through the ventricles, it generates the "QRS complex" on the EKG. This process of contracting and relaxing controls blood flow through the heart and to the rest of the body.
There are many conditions that can cause a person to have an irregular EKG reading, and in some cases, an irregular EKG reading can be normal for certain individuals.
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Heart block: when electrical signals are weakened or blocked
The heart is a pump made up of muscle tissue. Like all muscles, it requires a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the heart's various chambers. This electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat.
Electrical signals are generated by the sinus node (also called the sinoatrial node, or SA node). This is a small mass of specialized tissue located in the right upper chamber (atria) of the heart. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions.
Heart block is a conduction disorder in which the heart's electrical signals are unable to move from the atria to the ventricles. This interference prevents the atria from telling the ventricles when to contract and pump blood. In most cases of heart block, the electrical signals are weakened but do not stop completely. There are three degrees of heart block severity.
First-degree heart block is the least severe and most common type of heart block. The electrical signals are not completely blocked but slow down as they move from the atria to the ventricles. They continue to reach the ventricles without interruption, just slower than normal. People with first-degree heart block may not have any symptoms and may not need treatment.
Second-degree heart block occurs when only some electrical signals from the heart's upper chambers reach the lower chambers. This can cause the heart to miss beats and beat slowly and irregularly. There are two types of second-degree heart block: Mobitz type I and Mobitz type II. In Mobitz type I, the electrical signals get slower and slower between beats. In Mobitz type II, the electrical signals sometimes get to the ventricles, and sometimes they don't. This type of heart block can often progress to third-degree heart block and is, therefore, more dangerous.
Third-degree heart block (complete heart block) is the most severe form of heart block. In this type of block, electrical signals don't pass from the atria to the ventricles at all for periods of time. There is a complete failure of electrical conduction. This can result in no pulse or a very slow pulse. Third-degree heart block negatively affects the heart's ability to pump blood out to the body and usually requires a pacemaker for treatment.
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How the heart's electrical system affects heart rate
The heart is a pump made of muscle tissue that requires a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its chambers. This electrical conduction system is made up of a network of nodes, cells, and signals that controls the heartbeat.
The electrical impulse that stimulates the heart originates in a small mass of specialized tissue called the sinus node (also called the sinoatrial node or SA node). The sinus node is located in the upper portion of the right atrium, which is one of the four chambers of the heart. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. This electrical stimulus is like electricity travelling through wires to an appliance in your home.
The electrical impulse first spreads across the right and left atria, causing them to contract. This action, known as atrial depolarization, pushes blood into the right and left ventricles, which are the bottom two chambers of the heart. The atria contract a fraction of a second before the ventricles so that their blood empties into the ventricles before the ventricles contract. This process is important for maintaining the proper flow of blood through the heart and to the rest of the body.
As the electrical impulse passes through the atria, it generates a "P" wave on an electrocardiogram (EKG), which is used to assess the heart's electrical system and any related medical conditions. When the electrical impulse reaches the AV disc, it is stopped, except in the AV node, where it travels at a slow, controlled rate toward the ventricles. This pause allows the atria to contract fully and empty blood into the ventricles before the ventricles contract.
The electrical system of the heart controls the heartbeat, with each electrical impulse generating one heartbeat. Therefore, the number of electrical impulses produced by the sinus node determines the heart rate. When the SA node fires at an increased rate, it can lead to sinus tachycardia, which refers to a rapid heart rate. On the other hand, when the electrical pathway of the heart is disrupted, it can lead to conduction disorders, such as heart block, where the electrical signals are unable to move from the atria to the ventricles. In severe cases of heart block, a person's pulse may slow dramatically or stop completely, requiring the use of a pacemaker.
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Frequently asked questions
A heart's electrical conduction system is a network of nodes, cells and signals that controls the heartbeat. Each time the heart beats, electrical signals travel through the heart, causing it to expand and
The sinus node, or sinoatrial node (SA node), is a small mass of specialised tissue located in the right upper chamber (atrium) of the heart. It is the heart's natural pacemaker and generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions.
The electrical impulse originates in the sinus node and spreads across the right and left atria, causing them to contract and push blood into the ventricles. The electrical signal then reaches the atrioventricular (AV) node, where it is briefly delayed before continuing into the ventricles.
Abnormalities in the heart's electrical system can cause the heart to beat too quickly, too slowly or irregularly. This condition is called arrhythmia and can be treated with an automated external defibrillator (AED). Another condition is heart block, where the electrical signals are unable to move from the atria to the ventricles, which can cause symptoms such as fatigue, dizziness and fainting.
