Athena Vale
The human heart is a vital organ that pumps blood throughout the body. It is the main organ of the cardiovascular system, a network of blood vessels that supplies blood to the entire body. The heart is composed of cardiac muscle, also known as myocardium, which is one of three types of muscle tissues found in the human body, the other two being smooth muscle and skeletal muscle. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The cardiac muscle is responsible for the contractility of the heart, which is the pumping action that sends blood throughout the body.
| Characteristics | Values |
|---|---|
| Type of muscle | Cardiac muscle, also called heart muscle or [myocardium]; one of three types of vertebrate muscle tissues, the others being [skeletal muscle and smooth muscle] |
| Involuntary control | Yes |
| Location | [Wall of the heart] |
| Appearance | [Striated] (striped) |
| Contractibility | The [Cardiac muscle contracts and relaxes to send blood throughout the body; the [heart rate is controlled by the nervous system] |
| Composition | [Individual cardiac muscle cells] (cardiomyocytes) [joined by intercalated discs] and [encased by collagen fibers] |
| Electrical activity | [Cardiac muscle cells generate their own electrical impulses] which trigger [contractions] |
| Calcium | [Calcium is required for contraction], and [calcium ions combine with the regulatory protein troponin] to allow [myofilaments to slide past each other] |
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What You'll Learn
The heart is the only organ that is also a muscle
The heart is a vital organ that pumps blood throughout the body. It is also the main organ of the cardiovascular system, which delivers oxygen and nutrients to all the organs and tissues of the body. The heart is made up mostly of a special type of muscle tissue called cardiac muscle, which is specific to the heart. The heart is the only place in the body that has cardiac tissue.
The heart muscle is the myocardium or middle layer of the heart walls. The myocardium is responsible for the contractile function of the cardiac pump. The heart muscle is composed of cardiomyocytes, which form the thickest layer of every heart chamber. Cardiomyocytes have distinctive cellular and physiological features, allowing them to generate force to maintain adequate tissue and organ perfusion throughout the body.
The heart is regulated by both neural and endocrine control, but it is also capable of initiating its own electrical impulse that triggers the mechanical contraction that pumps blood. This is known as autorhythmicity. The heart maintains this capability throughout adulthood, with the fastest cells assuming control of the rate.
The heart is an organ that is essential for the body's overall health and function. Without the pumping action of the heart, blood would be unable to move through the circulatory system, and the body's organs and tissues would not be able to function properly. This is why it is very important to take good care of your heart through exercise, a healthy diet, and not smoking.
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Cardiac muscle is made of cardiac muscle tissue, or myocardium
The heart is the main organ of the cardiovascular system, a network of blood vessels that pumps blood throughout the body. The heart is the only organ that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle, which is involuntary and striated. This means that the movements of the heart are automatic and cannot be controlled by a person.
Cardiac muscle, also called myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The cardiac muscle forms a thick middle layer, with blood supplied via the coronary circulation. It is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix.
The myocardium found in the ventricles is thick to allow forceful contractions, while the myocardium in the atria is much thinner. The individual myocytes that make up the myocardium also differ between cardiac chambers. Ventricular cardiomyocytes are longer and wider, with a denser T-tubule network. The sheets of muscle that wrap around the left ventricle closest to the endocardium are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously.
Cardiac muscle cells work together to produce the rhythmic, wave-like contractions known as the heartbeat. The heart rate is controlled by the nervous system, which sends signals to tell the heart to beat slower during rest and faster during stress. The endocrine system also plays a role in controlling heart rate by sending out hormones that tell blood vessels to constrict or relax, which affects blood pressure.
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Heart rate is controlled by the nervous and endocrine systems
The heart is a vital organ that pumps blood throughout the body. It is the only organ that is also a muscle, made of a special type of muscle tissue called cardiac muscle. The heart is part of the cardiovascular system, which is influenced by the nervous and endocrine systems.
The nervous system helps control heart rate by sending signals that tell the heart to beat slower during rest and faster during stressful situations. The endocrine system, on the other hand, sends out hormones that affect blood pressure by telling blood vessels to constrict or relax. Hormones from the thyroid gland can also influence the heart to beat faster or slower.
The autonomic nervous system (ANS) is a component of the peripheral nervous system that controls the contraction of cardiac muscle, visceral activities, and glandular functions of the body. It regulates heart rate, blood pressure, body temperature, and other visceral activities that maintain homeostasis. The ANS has two interacting systems: the sympathetic and parasympathetic nervous systems, which have opposing effects on the heart.
The sympathetic nervous system (SNS) releases hormones like epinephrine and norepinephrine to accelerate the heart rate and prepare the body for stressful situations, or the "fight or flight" response. Conversely, the parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate and promote a restful state.
Factors such as stress, caffeine, and excitement can temporarily increase heart rate, while meditation and deep breathing can help to slow it down. Regular cardiovascular exercise can also decrease resting heart rate over time by increasing the heart's size, contractile strength, and length of time it fills with blood. This results in increased activity of the parasympathetic nervous system and decreased activity of the sympathetic nervous system.
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Heart muscle cells are striated, branched and involuntary
The heart is the main organ of the cardiovascular system, a network of blood vessels that pumps blood throughout the body. The heart walls are muscles that contract (squeeze) and relax to send blood throughout the body. The heart muscle, also called cardiac muscle or myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle.
Cardiac muscle is an involuntary, striated muscle that constitutes the main tissue of the heart wall. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). It is composed of individual cardiac muscle cells, also called cardiomyocytes, which are joined by intercalated discs to form long fibers. These discs are responsible for force transmission during muscle contraction. Each cell contains myofibrils, specialized protein contractile fibers of actin and myosin that slide past each other. These are organized into sarcomeres, the fundamental contractile units of muscle cells.
Cardiac muscle cells are the contracting cells that allow the heart to pump. Each cardiomyocyte needs to contract in coordination with its neighboring cells, working together to efficiently pump blood from the heart. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation.
Specialized modified cardiomyocytes known as pacemaker cells set the rhythm of the heart contractions. These cells are only weakly contractile and are connected to neighboring contractile cells via gap junctions. They are located in the sinoatrial node (the primary pacemaker) and the atrioventricular node (secondary pacemaker). Pacemaker cells carry the impulses that are responsible for the beating of the heart, spontaneously generating and sending out electrical impulses.
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Heart muscle cells are joined by intercalated discs
The heart is the only organ in the human body that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle. This muscle tissue is composed of individual heart muscle cells, or cardiomyocytes, which are connected by intercalated discs. These discs allow the cells to work as a single functional unit of contraction, called a syncytium, so that the heart can work like a pump.
Intercalated discs are complex structures that connect adjacent cardiac muscle cells. They are composed of three types of cell junctions: desmosomes, fascia adherens junctions, and gap junctions. Desmosomes are cell structures that anchor the ends of cardiac muscle fibres together, preventing separation during contraction. Fascia adherens junctions are anchoring sites for actin, connecting to the closest sarcomere. Gap junctions connect the cytoplasms of neighbouring cells electrically, allowing cardiac action potentials to spread between cells by permitting the passage of ions and producing depolarization of the heart muscle.
The contraction of individual cardiac muscle cells produces force and shortening in the muscle bands, with a resultant decrease in heart chamber size. Intercalated discs are, therefore, the major portal for cardiac cell-to-cell communication, which is required for coordinated muscle contraction and the maintenance of circulation. The coordinated contraction of the entire heart is called electric coupling.
The heart's ability to contract is due to its individual cells' ability to generate their own electrical impulses. These impulses trigger mechanical contractions that pump blood at a fixed pace without nervous or endocrine control. This ability is called autorhythmicity. The heart rate is determined by specialized cardiac muscle cells called pacemaker cells, which directly control heart rate.
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Frequently asked questions
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 wall of the heart.
The cardiac muscle contracts in a similar manner to skeletal muscle, although with some differences. Electrical stimulation triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, which causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling.
The heart is regulated by both neural and endocrine control, yet it is capable of initiating its own action potential followed by muscular contraction. The nervous system helps control heart rate by sending signals that tell the heart to beat slower during rest and faster during stress.
