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The human 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. This electrical impulse originates in the heart's natural pacemaker, called the sinus node, and results in the heartbeat. The heartbeat consists of two phases: diastole and systole. The cardiac muscle, also called the myocardium, is one of the three major categories of muscles in the human body.
| Characteristics | Values |
|---|---|
| Name | Cardiac muscle, myocardium |
| Composition | Sarcomeres, cardiomyocytes |
| Control | Involuntary |
| Location | Heart |
| Function | Contraction, pumping action |
| Energy Source | ATP |
| Conditions | Cardiomyopathy, arrhythmogenic right ventricular dysplasia |
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Cardiac muscle tissue
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue, also called the myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle in the body, along with skeletal and smooth muscle. The myocardium is surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle cells (cardiomyocytes) are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialised ion channels that skeletal muscle does not possess. Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
Cardiac muscle cells are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organise into thick and thin filaments, called myofilaments. Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin. The myofilaments slide past each other as the muscle contracts and relaxes. This process activates from the release of calcium from the sarcoplasmic reticulum (SR) when delivering an action potential to the muscle, in a process called excitation-contraction coupling. The sliding of actin and myosin past each other produces the formation of "cross-bridges", which causes contraction of the heart and generation of force.
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Electrical impulses
The heart is a pump made up of muscle tissue. Like all muscles, the heart 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.
The heart's electrical conduction system is a network of specialised muscle cells that send signals to the rest of the heart muscle, causing it to contract. This network is called the cardiac conduction system, and its main components are the SA node, AV node, bundle of HIS, bundle branches, and Purkinje fibres.
The SA node, or sinus node, is a small mass of specialised tissue located in the right upper chamber (atria) of the heart. It generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. When the sinus node fires, a wave of electricity sweeps across the atria, causing the upper chambers to contract.
The electrical impulse then travels from the atria to the ventricles via the atrioventricular (AV) node, located in the centre of the heart. From the AV node, the electrical impulse moves through the specialised fibres called the Bundle of His and bundle branches to transmit the impulse to the ventricular muscle, resulting in ventricular contraction.
The coordinated contraction of the atria and ventricles is essential for pumping blood into circulation. This contractile function of the heart requires ATP, which can be obtained from various substrates, including fatty acids, carbohydrates, proteins, and ketones.
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Contractions
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 heart contracts about 60 to 100 times a minute at rest, depending on a person's age. Each contraction of the ventricles represents one heartbeat.
Cardiac muscle tissue is one of the three types of muscle tissue in the human body. It is also called the myocardium. The heart is made up of three layers—the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart.
Cardiac muscle cells (cardiomyocytes) are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscle does not possess. The sarcolemma also contains transverse tubules (t-tubules) that are highly branched invaginations that function in excitation-contraction coupling (ECC), action potential initiation and regulation, maintaining the resting membrane potential, and signal transduction.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interactions between these filaments form the basis of the sliding filament theory. Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials from one cell to the next in a phenomenon known as electrical coupling. Cardiac desmosomes are intercellular structures that anchor cardiac muscle fibers together and are vital in maintaining the structural integrity of the heart.
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Cardiomyopathy
The human heart is made up of three layers—the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, is responsible for the contractility of the heart and, therefore, its pumping action. Cardiomyopathy is a disease that weakens the myocardium, making it harder for the heart to pump blood effectively.
There are several types of cardiomyopathy, and the disease can affect people of any sex, race, or age. Hypertrophic cardiomyopathy, for example, poses a risk to young adults and even athletes. Peripartum cardiomyopathy affects some women before, during, or after pregnancy. Newborns and children can also develop cardiomyopathy, though in many cases, the cause may not be known.
The causes of cardiomyopathy can be varied. It can be acquired due to another disease, condition, or factor, or inherited through genetics. Risk factors include genetic predisposition, other medical conditions, unhealthy lifestyle choices, and extreme stress. Symptoms of cardiomyopathy include shortness of breath, fatigue, dizziness, fainting, swelling in the ankles or legs, and chest pain.
Treatment options for cardiomyopathy include lifestyle changes, medications, surgery, implanted devices to correct arrhythmias, and other nonsurgical procedures. While these treatments may not fully repair the heart muscle, they can help manage symptoms, prevent disease progression, and reduce the risk of sudden death.
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Exercise
The heart is a muscle, and like all muscles, 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 the various chambers of the heart. This electrical conduction system is known as the cardiac conduction system and is the network of nodes, cells, and signals that controls the heartbeat.
The cardiac conduction system sends out thousands of signals per day to keep the heart beating. The heart's electrical system determines how fast the heart beats. When you exercise, your heart beats faster, and your heart rate speeds up to get more oxygen to your muscles. This is an example of how the cardiac conduction system helps the heart speed up when the body needs more blood and oxygen.
The cardiac conduction system controls the rate and rhythm of the heartbeat. With each heartbeat, an electrical signal travels from the top of the heart to the bottom, causing the heart to contract and pump blood. This process includes the following steps: The signal begins in a group of cells called pacemaker cells, located in the sinoatrial (SA) node in the right atrium. The SA node is the heart's natural pacemaker, and it sends electrical impulses that start the heartbeat. The SA node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions.
To exercise the cardiac muscle, it is important to engage in regular aerobic exercise, which includes activities such as running, walking, swimming, cycling, dancing, and climbing stairs. These activities help strengthen the cardiac muscle, improving its efficiency and lowering the risk of stroke and heart attack. It is recommended to increase your activity level gradually and consult a healthcare provider for guidance on specific exercises, movements, or physical activities that can improve your cardiac health and overall well-being.
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Frequently asked questions
A heartbeat is caused by an electrical impulse travelling through the heart. This impulse causes the heart to contract and pump blood to the body.
The cardiac muscle, also called the myocardium, is responsible for the heartbeat. It is one of three types of muscle tissue in the human body.
The cardiac muscle is made up of cardiac muscle cells (cardiomyocytes) that contract together synchronously to enable the heart to work as a pump. The cardiomyocytes contain a single, centrally located nucleus, surrounded by a cell membrane called the sarcolemma.
The electrical impulse originates in the heart's natural pacemaker, called the sinus node or SA node. The impulse then travels through the conduction pathways, causing the heart's ventricles to contract and pump out blood.
