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Cardiac muscle, found in the walls of the heart, is a type of striated muscle. It is composed of cardiomyocytes and has a rectangular shape. Unlike skeletal muscle, cardiac muscle fibres are branched cells with 1-2 centrally located nuclei. Smooth muscle fibres, on the other hand, are spindle-shaped, with a single nucleus. This discussion will focus on the shape of cardiac muscle and how it differs from other muscle types, particularly smooth muscle.
| Characteristics | Values |
|---|---|
| Shape | Rectangular |
| Muscle Type | Striated |
| Muscle Tissue | Composed of cardiomyocytes |
| Muscle Cell Nucleus | Single, centrally located |
| Muscle Cell Length | 85-120 µm |
| Muscle Cell Diameter | 15-30 µm |
| Muscle Cell Structure | Branched |
| Muscle Cell Junctions | Intercalated discs |
| Muscle Contraction | Involuntary, strong, rhythmical |
| Muscle Function | Pumps blood into vessels of the circulatory system |
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What You'll Learn
- Cardiac muscle is striated and has a single, centrally located nucleus
- Cardiac muscle is involuntary, strong, and rhythmical in its contractions
- Intercalated discs allow cardiac muscle cells to contract in a wave-like pattern
- Cardiac muscle is the most hard-working muscle in the body
- Inadequate oxygenation is a major factor affecting the function of cardiac muscle
Cardiac muscle is striated and has a single, centrally located nucleus
Muscle tissue is classified into three types according to structure and function: striated (skeletal), smooth, and cardiac. Striated or skeletal muscle is made up of long cylindrical fibres and has many peripherally located nuclei. Cardiac muscle, on the other hand, is short and branched, and appears striated under a microscope. It is composed of cardiomyocytes, each of which contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. This membrane contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscle does not possess.
The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. It must contract with enough force to supply blood to meet the metabolic demands of the entire body. The cardiac muscle is the most hard-working muscle in the body, contracting and relaxing 60–100 times per minute from intrauterine life until death. The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, as it must force oxygenated arterial blood around the body.
The contractile walls of the heart are formed by cardiac muscle. Cardiac muscle cells are single cells that contract on their own intrinsic rhythms without any external stimulation. They attach to one another with specialized cell junctions called intercalated discs, which have both anchoring junctions and gap junctions. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
Cardiac muscle is a form of striated muscle but differs significantly from skeletal muscle. While the contraction of both cardiac and skeletal muscle is regulated by cytosolic Ca2+ ion concentration, the molecular basis of contraction differs between the two. For example, the cardiac muscle transverse (T) tubular system consists of much wider invaginations of the cell surface than those found in skeletal muscle.
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Cardiac muscle is involuntary, strong, and rhythmical in its contractions
Cardiac muscle, also known as myocardium or heart muscle, is one of three types of vertebrate muscle tissues found in the human body, the others being skeletal muscle and smooth muscle. It is a form of striated muscle, characterised by a similar arrangement of actin and myosin filaments to mediate contraction.
Cardiac muscle is involuntary in nature. The contraction of cardiac muscle is regulated by the cytosolic Ca2+ ion concentration, which is very similar to skeletal muscle. The cardiac muscle cell has one central nucleus, and is rectangular in shape. The contraction of cardiac muscle is involuntary, strong, and rhythmical.
The cardiac muscle is the most hard-working muscle in the body; it contracts and relaxes 60–100 times per minute from intrauterine life until death. Stress and physical activity can increase the number of beats per minute to well above 120, often for long periods. The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, as it has to force oxygenated arterial blood around the body.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments, the interactions between which form the basis of the sliding filament theory. The sarcomeres allow for contractility. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working to efficiently pump blood from the heart.
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Intercalated discs allow cardiac muscle cells to contract in a wave-like pattern
Cardiac muscle, or myocardium, is a type of striated muscle that is present only in the heart. It is composed of cardiomyocytes, or cardiac muscle cells, which are extensively branched and connected to one another at their ends by intercalated discs. Intercalated discs are complex structures that allow cardiac muscle cells to work as a single functional unit, contracting in a coordinated, wave-like pattern. This wave-like pattern of contraction allows the heart to work as a pump, forcing oxygenated arterial blood around the body through the vessels of the circulatory system.
Intercalated discs contain three types of cell junction: desmosomes, fascia adherens junctions, and gap junctions. Desmosomes are important in preventing separation during contraction by binding intermediate filaments and anchoring the cell membrane to the intermediate filament network. In other words, they hold the muscle fibres together when the heart contracts. Gap junctions, on the other hand, connect the cytoplasms of neighbouring cells electrically, allowing cardiac action potentials to spread between cardiac cells by permitting the passage of ions between them. This produces depolarization of the heart muscle, which is essential for muscle contraction.
The contractions of the heart, or heartbeats, are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure. The wave of contraction that allows the heart to work as a unit, or functional syncytium, begins with the pacemaker cells.
The sustained depolarization "plateau" produced by Ca2+ entry through voltage-gated calcium channels in the sarcolemma of cardiac muscle fibres is another feature of cardiac muscle that provides for a longer contraction than is produced by an action potential in skeletal muscle. Unlike skeletal muscle, a large percentage of the Ca2+ that initiates contraction in cardiac muscles comes from outside the cell rather than from the SR.
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Cardiac muscle is the most hard-working muscle in the body
The heart is the hardest-working muscle in the human body. It is the only organ that is also a muscle and is made of a special type of muscle tissue called cardiac muscle. This muscle tissue is responsible for the contractility of the heart, which allows it to pump blood through the cardiovascular system. The heart beats thousands of times a day, contracting and relaxing 60 to 100 times per minute from intrauterine life until death. This means that the cardiac muscle has to work extremely hard to keep the body alive and functioning properly.
The cardiac muscle is composed of cardiomyocytes and is a form of striated muscle, similar to skeletal muscle. It differs from skeletal muscle in that it is under involuntary control, meaning that it beats on its own without any conscious input. The contraction of cardiac muscle cells is regulated by cytosolic Ca2+ ion concentration, and the molecular basis of contraction is very similar to that of skeletal muscle. However, the cardiac muscle transverse (T) tubular system consists of much wider invaginations of the cell surface, and the sarcoplasmic reticulum associated with the T tubules is less organized than in skeletal muscle.
The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, as it is responsible for forcing oxygenated arterial blood around the body. Any factor that affects the function of this muscle can have a major impact on the left ventricle and its ability to function properly. One of the most important factors influencing cardiac muscle function is inadequate oxygenation, often due to an inadequate coronary artery supply. This can lead to heart disease, which is the leading cause of death worldwide.
To maintain the health of the cardiac muscle and the heart, it is important to exercise, provide proper nutrition and rest, and protect it from toxins. Maintaining a healthy cardiovascular system is essential for people of all ages, as poor cardiovascular health can lead to fatty deposits in the blood vessels (atherosclerosis), which is a primary cause of heart attacks and a leading cause of stroke. Additionally, diet and lifestyle factors, such as consuming foods high in saturated fat and cholesterol, can increase the risk of cardiovascular disease. Therefore, it is crucial to make healthy food choices and maintain a balanced lifestyle to support the hard-working cardiac muscle and promote overall health.
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Inadequate oxygenation is a major factor affecting the function of cardiac muscle
Cardiac muscle is a type of striated muscle, similar to skeletal muscle. It is composed of cardiomyocytes and is the most hard-working muscle in the human body, contracting and relaxing 60 to 100 times per minute from intrauterine life until death.
Myocardial oxygen consumption (MVo2) is the oxygen consumption of the heart muscle. It is the amount of oxygen consumed by the heart per unit of time. The cardiac oxygen consumption rate may be scaled to either cardiac mass or body mass to permit comparisons among hearts or animals of different sizes. Cardiac oxygen demand is primarily determined by the amount of work performed by the heart per unit of time, termed myocardial power output. Myocardial oxygen consumption is principally utilized for contraction, as basal metabolism comprises only 10-20% of total oxygen consumption.
Factors that increase myocardial oxygen demand include an increased heart rate, which results in a shorter diastolic filling period and decreased coronary blood flow. This can lead to inadequate blood flow and insufficient oxygen supply. Heart rate is considered the most important factor affecting myocardial oxygen demand. Other factors that increase myocardial oxygen demand include wall tension (left ventricular pressure and diastolic volume), contractility, and cardiac work.
Hypoxemia, or low blood oxygen levels, can occur due to various medical conditions, including sleep apnea, lung diseases, and heart defects. It can lead to mild symptoms such as headaches and shortness of breath, or severe consequences like interference with heart and brain function, and even death.
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Frequently asked questions
No, cardiac muscle is rectangular in shape. It is found in the walls of the heart and is under the control of the autonomic nervous system.
Spindle-shaped muscle, also known as smooth muscle, is found in the walls of all visceral organs except the heart. They are wide in the middle and tapered at both ends, much like a football.
Cardiac muscle is a type of striated muscle with a similar arrangement of actin and myosin filaments to mediate contraction. It is composed of cardiomyocytes and has intercalated discs that allow for synchronized contractions to pump blood out of the heart efficiently.
Unlike skeletal muscle, cardiac muscle fibers are branched cells with only 1-2 centrally located nuclei. Cardiac muscle also has a different molecular basis for contraction, with a higher reliance on cytosolic Ca2+ ion concentration.
