Otis Singleton
The human heart is a hollow muscle that pumps blood to the lungs and throughout the body. In order to do this, the heart requires an electrical impulse to stimulate a heartbeat. This electrical impulse is generated by the sinus node, a small mass of specialized tissue located in the upper right chamber of the heart. The sinus node acts as the heart's natural pacemaker, controlling the heart rate and causing the heart to contract in a coordinated manner. The electrical signal then travels through the atria, causing them to contract and pump blood into the ventricles. This process is essential for the proper functioning of the heart and ensures that the heart beats at a rate that meets the body's demands.
| Characteristics | Values |
|---|---|
| Purpose of the electrical system of the heart | To coordinate the pumping of the four chambers of the heart and to control the heart rate |
| Heart's "natural pacemaker" | Sino-atrial (SA) node, a small area of special electrical tissue high on the right side of the heart that starts the electrical signal |
| Location of SA node | Upper part of the heart's right atrium |
| Function of SA node | Sends electrical impulses that start the heartbeat |
| Heartbeat range | 60-190 times per minute, depending on the age and activity level of the person |
| Heartbeat abnormalities | Arrhythmia, which causes the heart to beat too quickly, too slowly, or irregularly |
| Treatment for arrhythmia | Electric shock from an automated external defibrillator (AED) |
| Conduction disorder | When the heart's electric pathway is disrupted, increasing the risk of major complications, including cardiac arrest |
| Treatment for conduction disorder | Regular exercise and a heart-healthy diet |
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What You'll Learn
- The sinus node, or SA node, acts as the heart's pacemaker
- Electrical signals travel through the atria, causing them to contract
- The atrioventricular node, or AV node, slows down the electrical impulses
- The bundle of His carries the electrical signal to the Purkinje fibres
- The Purkinje fibres deliver electrical signals to the ventricles, causing them to contract
The sinus node, or SA node, acts as the heart's pacemaker
The SA node is the heart's natural pacemaker because it sets the rhythm and rate of the heart. In a healthy heart, the SA node continuously produces action potentials, or electrical impulses, 60 to 100 times per minute under normal conditions. These impulses travel through the heart's electrical conduction system, causing the heart to contract in a coordinated manner. The rate of action potentials produced, and therefore the heart rate, is influenced by the nerves that supply it. The autonomic nervous system regulates the firing of the sinus node. Parasympathetic input slows down the rate of action potential production, thereby decreasing the heart rate, while sympathetic input increases it.
The SA node was first discovered by medical student Martin Flack in the early 1900s. It 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 sinus node is approximately 15 mm long, 3 mm wide, and 1 mm thick.
Dysfunction of the SA node, also known as sick sinus syndrome, can cause problems with the heart's rhythm and rate. This can include a slow heart rate (bradycardia) or a fast heart rate (tachycardia). Treatment for sick sinus syndrome may include medication or a permanent pacemaker.
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Electrical signals travel through the atria, causing them to contract
The heart is a hollow muscle that is a little larger than a person's fist. It is a pump made up of four chambers. The two upper chambers are called the atria, and the two lower chambers are called the ventricles. The atria receive blood from the body and empty it into the ventricles.
The electrical system of the heart coordinates the pumping of the four chambers and controls the heart rate. The sinus node (also called the sinoatrial node or SA node) is the heart's natural pacemaker. It is a small mass of specialized tissue located in the right upper chamber (atrium) of the heart. The sinus node 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 atrium and the left atrium, causing both atria to contract. This is referred to as atrial depolarization, which pushes blood into the ventricles.
As the electrical impulse passes through the atria, it generates a P wave on an EKG. When the wave of electricity reaches the AV disc, it is stopped, except in the AV node. The AV node, located near the central area of the heart, delays the SA node's electrical signal by a fraction of a second. This delay ensures that the atria are empty before the contraction stops.
From the AV node, the electrical signal travels down through the bundle of His, which separates into the right and left bundle, and then out to the muscle fibres of the ventricles through the Purkinje fibres. As the impulse spreads, the muscles contract and the ventricles pump blood out to the body.
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The atrioventricular node, or AV node, slows down the electrical impulses
The human heart is a hollow muscle that is slightly bigger than a person's fist. It functions like a pump, with four chambers. The two upper chambers are called the atria, and the two lower chambers are called the ventricles. The heart requires an electrical impulse to beat and contract, which is provided by the sinus node (also called the sinoatrial node or SA node). The sinus node is a small mass of specialized tissue located in the right upper chamber (atria) of the heart. It generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions.
The electrical impulse then travels from the sinus node to the atrioventricular node (AV node). The AV node is located between the atria and the ventricles. At the AV node, the electrical impulses are slowed down for a very short period, ensuring that the atria (upper chambers) are empty before the contraction stops. This delay is consistent, lasting only a fraction of a second. The AV node acts as a gatekeeper, allowing the electrical signal to pass through and continue down the conduction pathway into the ventricles.
The AV node is an essential component of the heart's electrical system, which includes the sinus node and other structures. This electrical system is responsible for coordinating the pumping action of the heart's four chambers and controlling the heart rate. The heart rate varies depending on the body's demands, increasing during physical activity and decreasing during rest or sleep. The AV node plays a crucial role in maintaining this delicate balance by regulating the timing of the electrical impulses.
The AV node is not the sole determinant of the heart rate, as it works in conjunction with other components of the cardiac conduction system. This system comprises a network of nodes, cells, and signals that collaborate to control the heartbeat. The autonomic nervous system, for instance, influences the speed at which the SA node sends electrical signals. Additionally, the bundle of His, a branch of nerve cells extending from the AV node, carries the electrical signal further down the conduction pathway to the Purkinje fibers, which then spread the signal through the ventricles, causing them to contract and pump blood.
Abnormalities in the AV node or the heart's electrical system can lead to arrhythmias, which are variations in heart rhythm. These abnormalities may include extra electrical pathways or an abnormal "focus" that acts like a second pacemaker, resulting in abnormally fast heartbeats. In other cases, conditions such as heart block or sinus node dysfunction can cause bradycardia, or a slow heartbeat, where the electrical signals cannot reach the lower chambers effectively. Treatment options for conduction disorders may include pacemakers or, in some cases, implantable cardioverter defibrillators.
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The bundle of His carries the electrical signal to the Purkinje fibres
The electrical system of the heart is a complex network of nodes, cells, and signals that controls the heartbeat. The cardiac conduction system sends a signal to start a heartbeat and also sends signals that tell different parts of the heart to relax and contract. The sinus node (also called the sinoatrial node or SA node) generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The SA node is a small area of specialised electrical tissue located in the upper right chamber (atrium) of the heart.
The electrical impulse originates in the sinus node and spreads across the right and left atria, causing both atria to contract. This is called atrial depolarisation, which pushes blood into the right and left ventricles. As the electrical impulse passes through the atria, it generates a "'P' wave on an EKG". The P wave can be seen on the left side of an EKG graph.
The electrical impulse then travels from the sinus node to the atrioventricular node (AV node), where it is slowed down for a very short period before continuing down the conduction pathway. The AV node is located between the atria and the ventricles. The bundle of His is a branch of nerve cells that extends from the AV node and receives the electrical signal from the AV node. It carries the electrical signal to the Purkinje fibres.
The bundle of His runs down the length of the septum (wall) that separates the right and left ventricles. The bundle of His has two branches: the left bundle branch and the right bundle branch. The left bundle branch sends electrical signals through the Purkinje fibres to the left ventricle, while the right bundle branch sends electrical signals to the right ventricle. The Purkinje fibres are specialised nerve cells that send electrical signals very quickly to the ventricles. When the Purkinje fibres deliver electrical signals to the ventricles, the ventricles contract and pump out blood.
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The Purkinje fibres deliver electrical signals to the ventricles, causing them to contract
The human heart is a complex organ with a network of nodes, cells, and signals that work together to control the heartbeat. The cardiac conduction system is an essential component of the heart's electrical system, coordinating the pumping action of the four chambers of the heart and controlling the heart rate.
The Purkinje fibres are a crucial part of the cardiac conduction system. Named after Jan Evangelista Purkyně, these specialized conducting fibres are located in the inner ventricular walls of the heart, in a space called the subendocardium. They are composed of electrically excitable cells, which are larger than cardiomyocytes and have a higher number of mitochondria. This unique structure enables Purkinje fibres to conduct cardiac action potentials more rapidly and efficiently than other cells in the heart's electrical conduction system.
The Purkinje fibres receive electrical signals from the atrioventricular bundle, also known as the bundle of His. This bundle is a collection of nerve cells that extend from the AV node, located between the atria and ventricles. The bundle of His divides into two branches: the left bundle branch and the right bundle branch. These branches transmit the electrical impulse to the Purkinje fibres in the respective left and right ventricles.
The Purkinje fibres then deliver the electrical signals to the muscle fibres of the ventricles, causing them to contract. This contraction of the ventricles generates the force required to eject blood out of the heart. The left ventricle pumps blood to the systemic circulation, supplying oxygenated blood to the body, while the right ventricle pumps blood to the pulmonary circulation, sending deoxygenated blood to the lungs for oxygenation.
The coordinated contraction of the ventricles, facilitated by the Purkinje fibres, ensures the efficient pumping of blood and helps maintain a healthy and consistent heart rhythm. The Purkinje fibres act as the "thin wires" that spread the electrical signal, allowing the heart to contract in a synchronized manner. This synchronization is vital for the proper functioning of the heart and the overall circulation of blood throughout the body.
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Frequently asked questions
The electrical system of the heart coordinates the pumping of the four chambers of the heart and controls the heart rate.
The electricity in the heart comes from the sinus node (also called the sinoatrial node or SA node), a small mass of specialised 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. The electrical impulse then travels from the sinus node to the atrioventricular node (AV node), where it is slowed down for a fraction of a second, before continuing down the conduction pathway into the ventricles.
When the electrical signal reaches the ventricles, the ventricles contract and pump out blood.
Abnormalities in the heart's electrical system can cause the heart to beat too quickly, too slowly, or irregularly, a condition known as arrhythmia. In some cases, a pacemaker may be required to regulate the heartbeat.
