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The human heart is a muscular organ that pumps blood throughout the body. It is made up of cardiac muscle, also known as myocardium, which is one of the three major categories of muscles in the human body. The cardiac muscle is responsible for the contractility of the heart, allowing it to pump blood. The heart's electrical conduction system, also known as the cardiac conduction system, plays a crucial role in controlling the heartbeat by sending electrical signals that coordinate the contraction of the heart's chambers. This system includes nodes such as the sinoatrial (SA) node, which acts as the heart's natural pacemaker by generating electrical impulses that initiate each heartbeat. The coordination of these electrical impulses and the contraction of cardiac muscle fibres work together to maintain the heartbeat and pump blood efficiently.
| Characteristics | Values |
|---|---|
| Name | Cardiac muscle, also called myocardium |
| Composition | Sarcomeres, striated, branched muscle cells (cardiomyocytes) with many mitochondria |
| Control | Involuntary |
| Function | To pump blood into circulation by generating sufficient force |
| Heartbeat | Heartbeat is the contraction of the heart to pump blood to the lungs and the rest of the body |
| Regulation | Electrical conduction system that coordinates the contraction of the various chambers of the heart |
| Electrical Stimulus | Generated by the sinus/sinoatrial (SA) node, a small mass of specialized tissue located in the right upper chamber (atria) of the heart |
| Rate of Electrical Stimulus | 60 to 100 times per minute under normal conditions |
| Heartbeat Sound | "Lub-DUB" |
| Pulse | Rate of heartbeat |
| Conduction System | A network of nodes, cells, and signals that controls the heartbeat |
| Nodes | Sinoatrial (SA) node, atrioventricular (AV) node, left bundle branch, right bundle branch, bundle of His, and Purkinje fibers |
| Functions of Nodes | SA node sends signals to make the heart beat; AV node carries electrical signals from the upper chambers to the lower ones; left and right bundle branches send electrical impulses to the left and right ventricles, respectively; bundle of His sends impulses from the AV node to the Purkinje fibers; Purkinje fibers make the heart ventricles contract and pump out blood |
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What You'll Learn
The cardiac conduction system
Upon reaching the atrioventricular (AV) node, the signal is briefly delayed before continuing down the conduction pathway into the bundle of His. The bundle of His divides into right and left bundle branches to stimulate the right and left ventricles. The wave of excitation then spreads along the ventricles through the Purkinje fibres, causing them to contract and pump blood out to the body.
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Electrical impulses
The heart is a pump made up of muscle tissue and is the main organ of the cardiovascular system, a network of blood vessels that pumps blood throughout the body. 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 the network of nodes, cells, and signals that controls the heartbeat.
The Purkinje fibres in the ventricles cause them to contract and deliver blood out to the body. The SA node creates an excitation signal, which is an electrical signal that travels through the conduction pathway of the heart. The cardiac action potential lasts approximately 200 ms and is divided into five phases: resting, upstroke, early repolarization, plateau, and final repolarization. The heart's electrical conduction system sends out thousands of signals per day to keep the heart beating. The electrical coupling of gap junctions between adjacent cardiomyocytes allows for the propagation of coordinated action potentials from one cell to the next.
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The SA node
In summary, the SA node plays a vital role in regulating the heartbeat and maintaining proper heart function. Its continuous generation of electrical impulses sets the rhythm and rate of the heart, ensuring that blood is pumped efficiently throughout the body.
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Cardiomyocytes
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. Cardiomyocytes are the cells responsible for the rhythmic beating of the heart. They are the smallest constituents of the myocardium.
During fetal and postnatal development, cardiomyocytes become terminally differentiated muscular cells that are connected end-to-end by gap junctions, allowing concerted contractile activity. The contraction-relaxation cycle of cardiomyocytes is orchestrated by cyclic increases and decreases in intracellular Ca2+ initiated by depolarization of the sarcolemma and sustained by Ca2+ release and re-uptake by the sarcoplasmic reticulum. When stressed, cardiomyocytes undergo hypertrophic growth and apoptotic responses in vivo as well as in cell culture models. Such changes predispose the heart to failure in the longer term.
Embryonic cardiomyocytes develop into a linear heart tube that subsequently undergoes rightward looping to initiate a primitive heart structure. Cardiomyocytes are generated through reprogramming, and substantial progress has been made in this field.
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The heart's electrical system
The heart is a pump made of muscle tissue that requires a source of energy and oxygen to function. The heart's electrical system, also known as the cardiac conduction system, is responsible for regulating the heart's pumping action through electrical impulses. This system coordinates the contraction of the heart's chambers and ensures a steady and even heart rate.
The cardiac conduction system consists of a network of nodes, cells, and signals that work together to control the heartbeat. The process begins with an electrical impulse generated by the sinus node, also known as the sinoatrial node (SA node) or the heart's natural pacemaker. This small mass of specialized tissue is located in the right upper chamber or atrium of the heart. The SA node generates electrical impulses regularly, typically 60 to 100 times per minute under normal conditions.
The electrical impulse travels from the SA node to the atrioventricular node (AV node), where it is briefly slowed down before continuing through the conduction pathway. The AV node is located in the middle of the heart, between the atria and ventricles. From the AV node, the electrical signal spreads through the right and left ventricles, causing these chambers to contract and pump blood to the organs and lungs, respectively.
The Purkinje fibres in the ventricles cause them to contract and deliver blood to the body. The heart's electrical system ensures that the atria contract a fraction of a second before the ventricles, allowing blood to empty into the ventricles before they contract and pump blood out. This coordinated contraction maximizes the efficiency of the beating heart.
Disruptions in the heart's electrical system can lead to conduction disorders, such as heart block, where the electrical signals are unable to move from the atria to the ventricles. This can result in symptoms like fatigue, dizziness, or fainting. In some cases, a permanent pacemaker may be required to treat conduction disorders and restore regular heart function.
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Frequently asked questions
The heart is made up of cardiac muscle, which is responsible for its contractility and pumping action.
The cardiac conduction system, the heart's electrical system, controls the heartbeat. Electrical signals move through the heart, making it beat. The SA node, located in the right atrium, acts as the heart's pacemaker by generating electrical impulses that trigger each heartbeat.
A heartbeat is the contraction of the heart, which pumps blood to the lungs and the rest of the body.
