Umair Gaines
The heart is a pump made up of muscle tissue. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart. The cardiac conduction system is the network of nodes, cells, and signals that controls the heartbeat. Electrical signals move through the heart, making it beat. The SA node, located in the right atrium, is the heart's natural pacemaker. It sends electrical impulses that start the heartbeat. These impulses then travel to the AV node, which is located in the interatrial septum. After a short delay, the electrical signal is conducted through the left and right bundle branches of His to the respective Purkinje fibers. The Purkinje fibers are specialized nerve cells that send electrical signals very quickly to the heart's right and left ventricles.
| Characteristics | Values |
|---|---|
| Name of cell type | Sinoatrial (SA) node cells |
| Location | Upper part of the heart's right atrium |
| Function | Sends electrical impulses that start the heartbeat |
| Backup | Lower segments of the conduction system act as backup pacemaker cells when the SA node isn't working well |
| Control | Autonomic nervous system controls how quickly or slowly the SA node sends electrical signals |
| Rate of electrical impulses | 60 to 100 times per minute under normal conditions |
| Conduction pathway | SA node -> Atria -> AV node -> Bundle of His -> Bundle branches -> Purkinje fibers -> Ventricles |
| Bundle branches rate of impulses | 20-30 impulses per minute |
| Purkinje fibers rate of impulses | 15-20 impulses per minute |
| Time taken for electrical impulse to reach ventricular muscle cells | Approximately 75 ms |
| Time taken for total impulse initiation in SA node until ventricular depolarization | Approximately 225 ms |
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What You'll Learn
The SA node, or sinus node, is the heart's pacemaker
The SA node, or sinus node, is a group of specialised myocardial conducting cells located in the upper back wall of the right atrium of the heart. It is also referred to as the sinoatrial node, the sinuatrial node, or the Keith-Flack node. The SA node is approximately 15 mm long, 3 mm wide, and 1 mm thick, and is located directly below and to the side of the superior vena cava, a large vein that brings oxygen-poor blood from the body to the heart.
The SA node is the heart's natural pacemaker. It generates electrical impulses that set the rhythm and rate of the heart, causing it to contract. These electrical impulses, known as cardiac action potentials, travel through the heart's electrical conduction system, resulting in myocardial contraction and blood distribution to the rest of the body. The SA node continuously produces action potentials, setting the rhythm of the heart, also known as the sinus rhythm. 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, decreasing the heart rate, while sympathetic input increases the rate of action potential production, increasing the heart rate. This regulated control of the sinus node allows the heart to adapt to various physiologic stressors placed on the body, such as the increased oxygen demand during exercise.
The SA node is made up of cells known as pacemaker cells, which can spontaneously generate electrical impulses. These cells do not have a resting potential, and their integrated activity forms the SA node. The first cell to produce the action potential in the SA node isn't always the same, and this is known as pacemaker shift. In certain animal species, a superior shift, where the cell that produces the fastest action potential in the SA node is higher than previously, can result in an increased heart rate. Conversely, an inferior shift, where the cell producing the fastest action potential is lower than before, can lead to a decreased heart rate.
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Electrical signals travel to the AV node
The cardiac conduction system is the network of nodes, cells, and signals that controls the heartbeat. Electrical signals move through the heart, making it beat. The SA node, or sinus node, is the heart's natural pacemaker. It sends electrical impulses that start the heartbeat. The SA node is located in the upper part of the heart's right atrium.
The electrical impulse then travels from the sinus node across the cells of the heart's right and left atria. The signal travels to the AV node (atrioventricular node). The AV node is a tiny "button" of specialized cells located near the center of the heart. It is on the right side of the atrial septum at the junction of the atria and ventricles. The AV node controls the passage of the heart's electrical signal from the atria to the ventricles.
In the AV node, the impulses are slowed down for a very short period. This allows the atria to contract a fraction of a second before the ventricles. This delay ensures that the atria are empty before the contraction stops. After passing through the AV node, the electrical current then continues down the conduction pathway, through a pathway called the bundle of His, and into the ventricles.
The bundle of His is a branch of nerve cells that extends from the AV node. It carries the electrical signal from the AV node to the Purkinje fibers. The bundle of His runs down the length of the septum that separates the right and left ventricles. The Purkinje fibers are branches of specialized nerve cells that send electrical signals very quickly to the heart's right and left ventricles. When the Purkinje fibers deliver electrical signals to the ventricles, the ventricles contract.
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The bundle of His separates the right and left ventricles
The heart is a pump made up of muscle tissue. It needs 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. The cardiac conduction system is the network of nodes, cells, and signals that controls the heartbeat. Electrical signals move through the heart, making it beat.
The bundle of His is an important part of the electrical conduction system of the heart. It transmits impulses from the atrioventricular node, located at the anterior-inferior end of the interatrial septum, to the ventricles of the heart. The bundle of His runs down the length of the septum (wall) that separates the right and left ventricles. The bundle of His branches into the left and right bundle branches, which run along the interventricular septum. The left bundle branch further divides into the left anterior fascicle and the left posterior fascicle.
The bundle of His is a collection of heart muscle cells specialized for electrical conduction. It consists of muscle cells, transition cells, Purkinje cells, and pacemaker cells. The bundle of His has two branches, left and right, located between the atria and ventricles. The bundle of His moves electrical impulses quickly through the heart via its insulated muscle fibers. The electrical impulse moves into the ventricular septum. At this point, the bundle of His splits into left and right branches. The right bundle of His causes contraction of the right ventricle as it moves down the right side of the septum. The left branch is divided into anterior and posterior. The left branches cause contractions of the heart to the left ventricle and run down the left side of the septum.
The bundle of His is also called the atrioventricular bundle. They run from the atrium to the ventricles, creating electric impulses that cause contraction of the heart. Atrioventricular bundles are made up of fibers that create electrical signals that cause the heart to contract.
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The bundle branches carry signals to the Purkinje fibres
The bundle branches play a critical role in the transmission of electrical signals through the heart. The bundle of His, a branch of nerve cells, receives electrical signals from the AV node and carries them to the Purkinje fibres. The bundle of His runs along the septum, the wall that separates the right and left ventricles.
The bundle of His divides into two branches: the left bundle branch and the right bundle branch. These branches deliver electrical signals to the Purkinje fibres, which are found in the ventricle walls. The Purkinje fibres are specialised nerve cells that quickly transmit electrical signals to the ventricles, causing them to contract.
The left bundle branch sends electrical signals through the Purkinje fibres to the left ventricle, while the right bundle branch sends signals to the right ventricle. This coordinated process ensures the synchronised function of the ventricles and the rhythmic contraction of the heart.
The cardiac conduction system, which includes the bundle branches and Purkinje fibres, is responsible for generating and transmitting electrical impulses that control the heartbeat. The SA node, located in the upper right chamber of the heart, initiates the electrical impulse, which then travels through the conduction pathways, including the bundle branches, to stimulate the heart muscle and coordinate its contractions.
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The Purkinje fibres are specialised nerve cells
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 the various chambers of the heart. This electrical conduction system is a network of specialised muscle cells found in the heart's walls. These muscle cells send signals to the rest of the heart muscle, causing it to contract.
The AV node is located between the atria and ventricles. It receives electrical signals from the SA node, which is the heart's natural pacemaker. The SA node is located in the upper part of the heart's right atrium. The electrical signals generated by the SA node travel through the heart's conduction pathways and cause the ventricles to contract and pump out blood. The atria are stimulated first and contract for a short period before the ventricles. This delay allows the atria to empty their contents into the ventricles before the ventricles contract.
The cardiac conduction system contains specialised cells and nodes that control the heartbeat. The Purkinje fibres, as a part of this system, play a crucial role in transmitting electrical signals to the ventricles, ensuring the coordinated contraction of the heart chambers and maintaining the proper functioning of the heart.
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Frequently asked questions
The cardiac conduction system, a network of specialized muscle cells, carries electrical signals.
The cardiac conduction system is the heart's electrical system. It controls the heartbeat by sending electrical signals through the heart.
The main parts of the cardiac conduction system are the SA node, AV node, bundle of His, bundle branches, and Purkinje fibers.
Doctors use a test called an ECG (electrocardiogram) or EKG to assess the electrical activity of the heart. This test involves recording the electrical activity of the heart with several small stickers attached to the patient's chest.
