Logan Steele
The human body is made up of more than 600 muscles, each with a unique function. One such muscle is the cardiac muscle, also known as the myocardium, which is one of three types of vertebrate muscle tissues found within the human body. The cardiac muscle is an involuntary, striated muscle that constitutes the main tissue of the heart wall. It is responsible for the heart's pumping action, which supplies blood to the entire body. This muscle is composed of individual cardiac muscle cells, called cardiomyocytes, which are joined by intercalated discs and encased by collagen fibers and other substances that form the extracellular matrix.
| Characteristics | Values |
|---|---|
| Types | Cardiac muscle, skeletal muscle, and smooth muscle |
| Location | Only found in the heart |
| Composition | Individual cardiac muscle cells (cardiomyocytes) joined by intercalated discs |
| Appearance | Striated |
| Contractions | Involuntary and coordinated |
| Calcium | Release of calcium from the sarcoplasmic reticulum triggers contraction |
| T-tubules | Transmit electrical impulses, regulate calcium concentration, and facilitate mechano-electric feedback |
| Gap Junctions | Allow propagation of action potentials and enable synchronized contractions |
| Desmosomes | Anchor cardiac muscle fibers and maintain structural integrity |
| Nucleus | Typically only one per cell, contains the cell's genetic material |
| Pacemaker Cells | Set the rhythm of heart contractions, located in the sinoatrial node |
| Cardiomyopathy | A disease that affects cardiac muscle tissue, making it harder for the heart to pump blood |
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What You'll Learn
Cardiomyopathy
The heart is a muscular organ with a very special type of muscle tissue, known as cardiac muscle. This muscle tissue is unique to the heart and is responsible for the organ's ability to contract and pump blood around the body. When something goes wrong with this muscle, it can lead to a group of conditions known collectively as cardiomyopathy.
There are four main types of cardiomyopathy: dilated, hypertrophic, restrictive, and arrhythmogenic right ventricular. Dilated cardiomyopathy is the most common type, where the left ventricle of the heart becomes enlarged and cannot pump blood efficiently. Hypertrophic cardiomyopathy involves the heart muscle becoming abnormally thick, again affecting the heart's ability to pump blood. Restrictive cardiomyopathy is where the heart's ability to fill with blood is affected due to stiffened heart muscles, and arrhythmogenic right ventricular cardiomyopathy involves the replacement of heart muscle with scar tissue and fat, most commonly affecting the right ventricle.
It is important to see a doctor if you are experiencing any symptoms of cardiomyopathy, as early diagnosis and treatment can help improve your quality of life and manage the condition effectively. With proper management, many people with cardiomyopathy can lead full and active lives.
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Calcium release
Calcium plays a crucial role in the functioning of the cardiovascular system, specifically in the contraction of the cardiac muscle or myocardium. The cardiac muscle is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the heart wall.
The process of calcium-induced calcium release (CICR) is essential for cardiac muscle contraction. Pacemaker cells in the SA and AV nodes initiate an action potential, which is conducted around the heart via gap junctions. This action potential travels down the T-tubules, resulting in an influx of calcium ions into the sarcoplasm through voltage-operated calcium channels (VOCCs) and ryanodine receptors.
The calcium ions entering the sarcoplasm bind to cardiac troponin-C, causing a conformational change. This change moves the tropomyosin away from the actin-binding site, exposing it and initiating cross-bridge binding. Myosin heads then bind to actin, and ADP and inorganic phosphate are released from the myosin head, allowing the power stroke to occur. This results in the cardiac muscle contraction, which occurs via the sliding filament model, similar to skeletal muscle.
The calcium ions that trigger this process are released from the sarcoplasmic reticulum (SR), the internal calcium store of the cell. Gq-protein coupling facilitates this release, and it is particularly important in muscle types that require calcium-induced calcium release, like cardiac muscle. The release of calcium ions from the SR occurs through two mechanisms: via Ca2+ channels on the SR and through ryanodine receptors (RyR), which are a family of Ca2+ releasing channels.
During muscle relaxation, calcium is no longer bound to troponin-C, and the actin-binding site is covered, ending contraction. The calcium ions are transported back into the sarcoplasmic reticulum, and the muscle relaxes, allowing the heart to refill with blood before the next heartbeat.
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Electrical coupling
The cardiac muscle, also known as the myocardium, is one of the three types of vertebrate muscle tissues. It is an involuntary, striated muscle that makes up the main tissue of the heart wall.
Cardiac excitation-contraction coupling (EC coupling or cardiac EC coupling) is a vital process that involves the transmission of electrical signals in the form of action potentials, which cause mechanical changes in the heart muscle cells, or cardiomyocytes, leading to their contraction. This process is essential for the controlled beating of the heart, allowing blood to be pumped to the lungs and the rest of the body.
The process of electrical coupling in cardiomyocytes is facilitated by intercalated discs, which are complex adhering structures. These discs consist of three types of cell-cell junctions: fascia adherens junctions, desmosomes, and gap junctions. The intercalated discs provide low electrical resistance, enabling the free diffusion of ions and the propagation of action potentials from one cardiac muscle cell to the next.
Cardiac desmosomes are intercellular structures that play a crucial role in maintaining the structural integrity of the heart by anchoring cardiac muscle fibers together. They act as staples that hold the contracting cardiomyocytes physically attached to one another.
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Cardiovascular disease
CVDs are often the result of behavioural and environmental risk factors such as tobacco use, unhealthy diet, physical inactivity, harmful alcohol use, and air pollution. These risk factors can lead to intermediate risk factors such as raised blood pressure, blood glucose, and blood lipids, as well as overweight and obesity, which increase the likelihood of heart attack, stroke, and heart failure.
One of the major causes of heart attacks and strokes is atherosclerosis, a condition where plaque builds up in the walls of the arteries, narrowing them and making it harder for blood to flow through. If a blood clot forms, it can block the blood flow, leading to a heart attack or stroke.
Rheumatic heart disease, caused by damage to the heart valves and muscle from inflammation and scarring due to rheumatic fever, accounts for about 2% of CVD deaths globally. This condition mostly affects children in developing countries, especially in poverty-stricken areas.
The clinical care and treatment of CVDs focus on improving cardiac muscle performance and preventing further complications. Medications and lifestyle changes are often recommended to reduce risk factors and manage the disease. Early detection is crucial, as most CVDs can be prevented or managed through counselling and medicines.
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Cardiac output
CO is typically between 5 and 6 litres per minute in a person at rest, but can be over 35 litres per minute in elite athletes during exercise. The body's demand for oxygen changes with activity, and so the cardiac output is altered by modulating both heart rate and stroke volume. For example, during exercise, the body requires more oxygen, and so the cardiac output is increased.
There are a number of methods for measuring CO, both invasive and non-invasive. One non-invasive method uses ultrasound and the Doppler effect to calculate flow velocity and volume, and ultimately, cardiac output. An example of an invasive method is intracardiac catheterisation.
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Frequently asked questions
A cardiovascular muscle is a type of muscle tissue that is only found in the heart. It is also called cardiac muscle or myocardium.
Cardiovascular muscles perform involuntary, coordinated contractions that allow the heart to pump blood through the circulatory system.
Cardiovascular muscles are made up of cardiomyocytes, which are rectangular, branching cells that typically contain only one centrally-located nucleus.
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