Otis Singleton
The heart's electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat. The electrical stimulus is generated by the sinus node, a small mass of specialized tissue located in the upper right chamber (atria) of the heart. The sinus node, also known as the sinoatrial node (SA node), acts as the heart's natural pacemaker, sending electrical impulses that travel through the conduction pathways and cause the heart's ventricles to contract and pump blood out to the body. The Purkinje fibers, which are branches of specialized nerve cells, play a crucial role in transmitting electrical signals to the right and left ventricles. This intricate system ensures the coordination of the heart's contractions and the regulation of blood flow.
| Characteristics | Values |
|---|---|
| Name of the electrical stimulus | Sinus node, also called the sinoatrial node (SA node) |
| Location | Small mass of specialized tissue located in the right upper chamber (atria) of the heart |
| Function | Generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions |
| Conduction Pathway | The electrical stimulus travels down through the conduction pathways and causes the heart's ventricles to contract and pump out blood |
| Role of Atria | The 2 upper chambers of the heart (atria) are stimulated first and contract for a short period of time before the 2 lower chambers of the heart (ventricles) |
| Role of Ventricles | Each contraction of the ventricles represents one heartbeat |
| Role of Purkinje Fibers | Send electrical signals to the right and left ventricles |
| Role of Bundle of His | A branch of nerve cells that extends from the AV node and carries the electrical signal to the Purkinje fibers |
| Types of Cardiac Muscle Cells | Myocardial contractile cells and myocardial conducting cells |
| Myocardial Contractile Cells | Constitute 99% of the cells in the atria and ventricles and are responsible for contractions that pump blood through the body |
| Myocardial Conducting Cells | Form the conduction system of the heart and initiate and propagate the electrical impulse that triggers contractions |
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What You'll Learn
The sinus node (SA node)
The sinus node, also known as the sinoatrial node (SA node) or Keith-Flack node, is a group of specialized cells known as pacemaker cells. These cells produce an electrical impulse known as a cardiac action potential, which travels through the electrical conduction system of the heart, causing it to contract. The SA node is located in the wall (epicardium) of the right atrium, laterally to the entrance of the superior vena cava in a region called the sinus venarum. It is approximately 15 mm long, 3 mm wide, and 1 mm thick.
The SA node is the heart's natural pacemaker, setting the rhythm of the heart, also known as the sinus rhythm. It continuously produces action potentials, resulting in a normal heart rate of 60 to 100 beats per minute. The rate of action potentials produced, and therefore the heart rate, is influenced by the nerves that supply it.
The SA node cells are smaller and paler than the surrounding atrial cells, with an average cell size of 8 micrometers in diameter and 20-30 micrometers in length. They contain fewer mitochondria, myofibers, and a smaller sarcoplasmic reticulum, making them less equipped for contraction compared to atrial and ventricular cells. The SA node is insulated from the surrounding atrial cells by connective tissue and paranodal cells, which prevent the electrical activity of the atrial cells from affecting the SA node cells.
The electrical impulse generated by the SA node travels through the conduction pathways of the heart, causing the ventricles to contract and pump out blood. The atria are stimulated first and contract for a short period before the ventricles, ensuring that the atria empty their blood into the ventricles before the contraction occurs. This process of contracting and relaxing controls blood flow through the heart and to the rest of the body.
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Electrical signals
The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of the heart chambers. This electrical conduction system is made up of a network of nodes, cells and signals that control the heartbeat.
The electrical signal is generated by the sinus node, a small mass of specialised tissue located in the right upper chamber (atria) of the heart. The sinus node is also referred to as the sinoatrial node (SA node) and is the heart's natural pacemaker. The SA node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions.
The electrical signal then travels from the SA node across the cells of the heart's right and left atria. This is referred to as atrial depolarisation, which causes both atria to contract and push blood into the right and left ventricles. As the electrical impulse passes through the atria, it generates a "P" wave on an electrocardiogram (EKG). An EKG traces the movement of electrical signals across the heart and can be used to assess the rhythm of the heart and identify any irregularities.
After the atria, the electrical signal travels to the atrioventricular (AV) node, located between the atria and ventricles. The signal is slowed down in the AV node, which allows the atria to contract a fraction of a second before the ventricles, so that blood empties into the ventricles before they contract. The AV node is made up of nerve cells that extend into a bundle of His, which carries the electrical signal to the Purkinje fibres. The Purkinje fibres are specialised nerve cells that quickly send electrical signals to the heart's right and left ventricles, causing them to contract and pump blood out into the body.
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Conduction pathways
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 a network of nodes, cells and signals that controls the heartbeat. This system consists of specialised conduction cells that initiate and coordinate the contraction of the heart muscle. The conduction system in the heart contains specialised cells and nodes that control the heartbeat.
The SA node, or sinoatrial node, is a collection of specialised cells (pacemaker cells) that can spontaneously generate electrical impulses. The SA node is located in the upper wall of the right atrium and generates an electrical stimulus 60 to 100 times per minute under normal conditions. The wave of excitation created by the SA node spreads via gap junctions across both atria, resulting in atrial contraction. The electrical stimulus travels down through the conduction pathways, causing the ventricles to contract and pump out blood.
After the electrical impulses spread across the atria, they converge at the atrioventricular node (AV node), located within the atrioventricular septum. The signal is then conducted into 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. The bundle of His has two branches: the left bundle branch and the right bundle branch. These branches 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 ventricles, causing them to contract and pump out blood. This process of contracting and relaxing controls blood flow through the heart and to the rest of the body.
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Contractions
The heart is a pump made of muscle tissue. Like all muscles, it requires oxygen and energy to function. The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of the heart chambers. The heart's electrical conduction system sends out thousands of signals per day to keep the heart beating.
The electrical stimulus is generated in a special part of the heart muscle called the sinus node, or the sinoatrial node (SA node). This is a small mass of specialised tissue located in the right upper chamber (atrium) of the heart. The SA node is the heart's natural pacemaker, controlling the heart rate. The SA node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. This electrical pulse travels through the conduction pathways, causing the heart's ventricles to contract and pump out blood.
The conduction system in the heart contains specialised cells and nodes that control the heartbeat. These include myocardial contractile cells and myocardial conducting cells. Contractile cells conduct impulses and are responsible for the contractions that pump blood through the body. Conducting cells carry the electrical signals and control the heart's contractions. The myocardial conducting cells initiate and propagate the action potential (the electrical impulse) that travels throughout the heart and triggers the contractions.
The electrical impulse starts in the SA node and travels a set path through the upper chambers, the atria, causing them to contract and squeeze blood into the lower chambers. The electrical signal then reaches the atrioventricular (AV) node, located between the atria and ventricles. The AV node slows down the electrical impulses for a very short period, allowing the atria to contract a fraction of a second before the ventricles. After passing through the AV node, the electrical current continues down the conduction pathway, through a pathway called the bundle of His, and into the ventricles. The bundle of His 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, causing them to contract and deliver blood out to the body.
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Heart rate
The heart is a pump made of muscle tissue. Like all muscles, the heart requires oxygen and energy to function. The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of the heart chambers. This electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat.
The electrical impulse that triggers a heartbeat originates in the sinus node (also called the sinoatrial node, or SA node). The sinus node is a small mass of specialised tissue located in the right upper chamber (right atrium) of the heart. The sinus node functions as the heart's ""natural pacemaker", sending out a regular electrical pulse 60 to 100 times per minute under normal conditions. This electrical pulse travels through the conduction pathways, causing the heart's lower chambers (ventricles) to contract and pump blood out into the body.
The electrical impulse leaves the sinus node and travels through the upper chambers (atria), causing them to contract and squeeze blood into the lower chambers. The electrical signal then reaches the atrioventricular (AV) node, which is located between the atria and ventricles. The AV node slows down the electrical impulses for a very short period, allowing 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 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 fibres that carries the electrical signal from the AV node to the Purkinje fibres. The Purkinje fibres are specialised nerve cells that quickly send electrical signals to the heart's right and left ventricles, causing them to contract and deliver blood out to the body.
The heart rate, or the number of heartbeats per minute, is determined by the number of electrical impulses generated by the sinus node. In addition to the sinus node, the myocardial conducting cells also play a role in initiating and propagating the electrical impulse throughout the heart. These conducting cells make up about 1% of the cells in the heart and are similar in function to neurons. The coordination of electrical impulses and contractions ensures a steady and efficient heart rate.
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Frequently asked questions
The heart receives electrical impulses or signals that trigger the heartbeat.
The electrical stimulus originates in a small mass of specialized tissue called the sinus node (SA node or sinoatrial node). The SA node is located in the upper right chamber of the heart (right atrium).
The electrical stimulus travels through the heart via conducting cells and specialized nerve cells called Purkinje fibers. The conduction pathway includes the atria, the atrioventricular (AV) node, and the bundle of His, which carries the signal to the ventricles.
The electrical stimulus coordinates the contraction of the heart chambers, ensuring that blood is pumped efficiently to the body and lungs. The SA node acts as the heart's natural pacemaker, controlling the heart rate according to the body's needs.
