Beatrice Lang
The human heart is a pump made of muscle tissue. 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 a network of nodes, cells, and signals that control the heartbeat. Each time the heart beats, electrical signals travel through it, causing different parts of it to expand and contract. These electrical impulses are generated by the sinus node, also called the sinoatrial node or SA node, which is a small mass of specialized tissue located in the right upper chamber of the heart.
| 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. |
| How does it work? | The sinus node (also called the sinoatrial node or SA node) generates an electrical stimulus, which causes the heart's ventricles to contract and pump out blood. |
| How often does the sinus node generate an electrical stimulus? | The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. |
| What happens if the sinus node doesn't work properly? | If the sinus node doesn't work properly, the lower segments of the conduction system act as backup pacemaker cells. |
| What is bradycardia? | Bradycardia is a condition where the electrical impulses in the heart are too slow, causing a decrease in heart rate. |
| What is tachycardia? | Tachycardia is a condition where the electrical impulses in the heart are abnormally fast. |
| What is an electrocardiogram (EKG)? | An EKG is a test that measures the electrical activity of the heart and can detect irregularities in the heart's electrical system. |
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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 conduction pathway of the heart
- The atrioventricular (AV) node slows down electrical impulses
- The bundle of His carries electrical signals to the left ventricle
- Abnormalities in the heart's electrical system can cause arrhythmia
The sinus node, or SA node, acts as the heart's pacemaker
The heart's electrical conduction system sends signals through the heart to tell it when to beat. This system contains specialised cells and nodes that control the heartbeat. The sinus node, or SA node, acts as the heart's pacemaker.
The SA node is a crescent-like cluster of myocytes (specialised cardiac muscle cells) divided by connective tissue. 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 SA node has the highest inherent rate of depolarization, which is why it is referred to as the pacemaker of the heart.
The SA node generates electrical impulses that set the rhythm and rate of the heart. These impulses are known as cardiac action potentials. The SA node initiates an action potential that results in an electrical impulse travelling through the heart's electrical conduction system, causing myocardial contraction. The impulse spreads from the SA node to the atrial myocardial contractile cells and the AV node. The impulse takes approximately 50 milliseconds to travel between the SA node and 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 to ensure that the atria are empty before the contraction stops. The electrical signal then spreads through the lower chambers, and the ventricles contract, sending blood throughout the body.
The sinus node continuously generates electrical impulses, setting a healthy heart's normal rhythm and rate. The rate of action potentials produced and, therefore, the heart rate is influenced by the nerves that supply it. The autonomic nervous system controls how quickly or slowly the SA node sends electrical signals. Parasympathetic input slows down the rate of action potential production, thereby decreasing the heart rate, while sympathetic input increases the rate of action potential production, thereby increasing the heart rate. This allows the heart to adapt to various physiologic stressors placed on the body.
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Electrical signals travel through the conduction pathway of the heart
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 a network of nodes, cells, and signals that controls the heartbeat. Each time the heart beats, electrical signals travel through the conduction pathway of the heart.
The electrical impulse starts in the right side of the upper chamber in an area called the sinus node or sinoatrial (SA) node. The SA node is the heart's natural pacemaker and controls the heart rate. It generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The SA node sends electrical signals to the atria, causing them to contract and squeeze blood into the lower chambers. The electrical signal then reaches the atrioventricular (AV) node, which is located in the middle of the heart between the atrium and ventricle. The AV node delays the SA node's electrical signal by a fraction of a second, ensuring that the atria are empty before the contraction stops.
The signal then moves from the AV node through the bundle of His, a branch of nerve cells that extends from the AV node. The bundle of His runs down the length of the septum that separates the right and left ventricles. It has two branches: the left bundle branch and the right bundle branch. These branches send electrical signals through the Purkinje fibers to the left and right ventricles, causing them to contract and pump blood out to the body. The ventricles contract about 60 to 100 times a minute at rest, depending on a person's age.
The conduction system in the heart contains specialized cells and nodes that control the heartbeat. The SA node is the primary pacemaker, but when it isn't working well, the lower segments of the conduction system, such as the AV node and the bundle of His, can act as backup pacemaker cells. The autonomic nervous system controls the rate at which the SA node sends electrical signals, adjusting the heart rate based on physical activity and rest.
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The atrioventricular (AV) node slows down electrical impulses
The heart is a pump made of muscle tissue. Its pumping action is regulated by electrical impulses. The cardiac conduction system is the 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 atrioventricular (AV) node is located near the central area of the heart. It delays the SA node's electrical signal by a consistent amount of time (a fraction of a second) each time. The delay ensures that the atria (upper heart chambers) are empty before the contraction stops. The atria receive blood from the body and empty it into the ventricles (lower heart chambers). The bundle of His, a branch of nerve cells, extends from the AV node. This bundle of fibres receives the electrical signal from the AV node and carries it to the Purkinje fibres. The bundle of His runs down the length of the septum (wall) that separates the right and left ventricles. The atrioventricular bundle has two branches: the left bundle branch and the right bundle branch. These send electrical signals through the Purkinje fibres to the left and right ventricles respectively.
The Purkinje fibres are branches of specialised nerve cells that send electrical signals very quickly to the heart's right and left ventricles. They are found in the ventricle walls in the inner layer of tissue that lines the heart's chambers. When the Purkinje fibres deliver electrical signals to the ventricles, the ventricles contract, sending blood throughout the body.
The AV node is, therefore, an important component of the cardiac conduction system, playing a key role in the regulation of the heartbeat. By delaying the SA node's electrical signal, it ensures the proper functioning of the heart and the regulation of blood flow through the body.
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The bundle of His carries electrical signals to the left ventricle
The heart is a pump made up 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 the heart's various chambers. The heart's electrical conduction system sends out thousands of signals per day to keep the heart beating.
The bundle of His is a branch of fibres (nerve cells) that extends from the atrioventricular (AV) node. The AV node is located near the central area of the heart and is responsible for delaying the electrical signal from the SA node by a fraction of a second. This delay ensures that the atria (upper heart chambers) are empty before the contraction stops. The bundle of His receives the electrical signal from the AV node and carries it to the Purkinje fibres.
The bundle of His runs down the length of the septum (wall) that separates the right and left ventricles. The atrioventricular bundle 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. The Purkinje fibres are branches of specialized nerve cells that send electrical signals very quickly to the heart's left ventricle, causing it to contract and pump blood out to the body.
The bundle of His plays a crucial role in the heart's electrical conduction system by transmitting electrical impulses from the AV node to the left ventricle, ensuring the proper coordination of ventricular contraction and blood flow to the body.
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Abnormalities in the heart's electrical system can cause arrhythmia
The heart is a muscular pump 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 control the heartbeat.
The sinus node, also known as the sinoatrial (SA) node, is the heart's natural pacemaker and is responsible for generating electrical impulses that start the heartbeat. These electrical impulses travel through a set path, causing the heart to contract and pump blood. When the SA node is not functioning properly, the lower segments of the conduction system act as a backup pacemaker.
Abnormalities in the heart's electrical system can lead to arrhythmia, which is any problem with the rate or rhythm of the heartbeat. Arrhythmias can cause the heart to beat too fast (tachycardia), too slow (bradycardia), or erratically. This disruption can affect the heart's ability to pump blood effectively, impacting the functioning of the lungs, brain, and other organs.
There are several ways in which abnormalities in the heart's electrical system can cause arrhythmia:
- Changes to heart tissue: Damage to the heart's electrical system or stiffening/scarring of the heart tissue can interrupt the normal conduction pathway, leading to arrhythmia.
- Heart block: This occurs when the electrical signal starting in the upper portion of the heart cannot reach the lower chambers, resulting in a slow heartbeat (bradycardia).
- Sinus node dysfunction: The sinus node, which is the heart's natural pacemaker, may not function regularly, leading to a heartbeat that is too slow.
- Extra electrical pathways: In some cases, an extra electrical pathway forms between the atria and ventricles, allowing the electrical impulse to create a continuous loop, resulting in a rapid heartbeat.
- Acquired heart issues: Conditions such as rheumatic heart disease and Kawasaki disease, which often occur in children with other cardiac problems, can contribute to arrhythmia.
Treatment options for arrhythmia include medications, lifestyle changes, and the use of devices such as pacemakers and implantable cardioverter defibrillators (ICD).
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Frequently asked questions
The heart's electrical conduction system sends out thousands of signals per day to keep the heart beating. The cardiac conduction system sends signals through the heart to tell it when to beat. The electrical impulse originates in the sinus node, which is a small mass of specialized tissue located in the right upper chamber of the heart. The sinus node is the heart's natural pacemaker and controls the heart rate.
When the electrical impulses in the heart are too slow, it causes a decrease in heart rate, known as bradycardia. This can be caused by heart block, which occurs when the electrical signal that starts in the upper portion of the heart cannot get through to the lower chambers. It can also be caused when the sinus node, or the heart's "pacemaker", does not work with regularity, known as sinus node dysfunction.
When the electrical impulses in the heart are too fast, it causes an abnormally fast heart rate, known as tachycardia. This can be caused by an extra electrical path in addition to the normal path, either separate from or within the AV node. This extra pathway causes the electrical impulse to make a continuous loop, resulting in a rapid heartbeat.
