Otis Singleton
The electrical pathway of the heart, also known as the cardiac conduction system, is a fascinating network of nodes, cells, and signals that work together to control your heartbeat. Each heartbeat is initiated by electrical signals that travel through a specific pathway, starting with the sinoatrial (SA) node, which acts as the heart's natural pacemaker. Understanding this pathway is crucial for comprehending both the healthy functioning of the heart and various cardiac conduction system diseases, disorders, and abnormalities. This knowledge also has practical applications, such as interpreting the results of an electrocardiogram (ECG or EKG), a common medical test used to assess heart rhythm.
| Characteristics | Values |
|---|---|
| Starting point of electrical pathway | Sinoatrial (SA) node |
| Location of SA node | Upper part of the heart's right atrium |
| SA node controlled by | Autonomic nervous system |
| Next point in the pathway | Atrioventricular (AV) node |
| Location of AV node | Central area of the heart |
| Function of AV node | Delays the SA node's electrical signal |
| Pathway after AV node | Bundle of His |
| Bundle of His | Divides into right and left bundle branches |
| Function of bundle branches | Stimulate the right and left ventricles |
| Final point in the pathway | Purkinje fibers |
| Function of Purkinje fibers | Cause ventricles to contract and deliver blood to the body |
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What You'll Learn
The SA node
The rate at which the SA node sends out electrical signals is controlled by the autonomic nervous system. This system directs hormones that control heart rate based on activity. For example, during physical activity, the sympathetic nervous system increases the heart rate, while the parasympathetic nervous system slows it down during rest.
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The AV node
The atrioventricular (AV) node is a crucial component of the heart's electrical pathway, coordinating the beating in the top of the heart. It is located near the central area of the heart, at the lower back section of the interatrial septum, near the opening of the coronary sinus. The AV node is quite compact, measuring approximately 1 by 3 by 5 millimetres.
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 fibres, which stimulate the right and left ventricles. The bundle of His divides into right and left bundle branches, ensuring the stimulation of both ventricles.
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Bundle of His
The bundle of His is a crucial component of the heart's electrical conduction system, transmitting electrical impulses from the atrioventricular (AV) node to the left and right bundle branches, which then stimulate the left and right ventricles. This bundle was discovered by Wilhelm His Jr. in 1893, and it is approximately 1.8 cm long in an adult heart.
The bundle of His is composed of a specialised collection of heart muscle cells, including Purkinje-type cells, slender and broad transitional cells, and pacemaker cells. These cells work together to ensure the efficient transmission of electrical impulses, allowing for the synchronised contraction of the ventricles. The Purkinje-type cells, in particular, play a key role in electrical conduction and are characterised by their unique cellular structure.
The bundle of His is an essential link between the atria and ventricles, ensuring the proper functioning of the heart. It receives electrical impulses from the AV node, which is located at the anterior-inferior end of the interatrial septum, and then transmits these impulses to the bundle branches. This transmission results in the contraction of the ventricles, which is necessary for pumping blood out of the heart.
Disorders affecting the bundle of His can lead to heart blocks, which are classified based on the location of cellular damage. For example, blockages in the right or left bundle branches are referred to as "bundle branch blocks". Additionally, studies have found that direct His bundle pacing can improve cardiac function by enhancing the synchronisation of ventricular contraction.
The bundle of His is an important structure in the heart's electrical pathway, facilitating the transmission of electrical impulses and coordinating the contraction of the ventricles. Its unique cellular composition and location between the atria and ventricles contribute to its essential role in maintaining proper heart function.
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Bundle branches
The bundle branches are an essential part of the electrical conduction system of the heart. Also known as Tawara branches, they transmit cardiac action potentials (electrical signals) from the bundle of His to Purkinje fibres in the heart ventricles.
The bundle of His divides into two bundle branches: the left bundle branch and the right bundle branch. These branches stimulate the left and right ventricles, respectively. The left bundle branch further divides into the left anterior fascicle and the left posterior fascicle, leading to a network of thin filaments known as Purkinje fibres.
The bundle branches play a crucial role in the electrical conduction system of the heart by transmitting cardiac action potentials to the Purkinje fibres. When functioning correctly, these structures ensure the precise synchronization of ventricular contraction, optimizing blood ejection.
However, bundle branches are susceptible to injury or blockage, resulting in altered pathways for ventricular depolarization. Conditions such as underlying heart disease, myocardial infarction, or cardiac surgery can lead to bundle branch block, causing a delay or blockage in the pathway that electrical impulses travel to make the heart beat. This, in turn, can lead to an irregular heartbeat and other serious complications.
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Purkinje fibres
These fibres are composed of electrically excitable cells and are larger than cardiomyocytes with fewer myofibrils and many mitochondria. They conduct cardiac action potentials more quickly and efficiently than any of the other cells in the heart's electrical conduction system.
The electrical origin of Purkinje fibres comes from the sinoatrial node (SA node). 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, directing hormones that control heart rate based on activity and state of rest.
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Frequently asked questions
The first step is the generation of an electrical stimulus in the sinus node, also known as the sinoatrial (SA) node.
The electrical impulse then travels through the right atrium via the internodal pathways, including the anterior, middle, and posterior tracts.
The impulse reaches the atrioventricular (AV) node, where it is slowed down briefly before continuing through the bundle of His.
The bundle of His divides into right and left bundle branches, stimulating the right and left ventricles, causing them to contract and pump blood out to the body.
