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There are three types of muscle in the human body: smooth muscle, cardiac muscle, and skeletal muscle. Smooth muscle is found in the internal organs and blood vessels and is involuntary. Cardiac muscle is only found in the heart and is involuntary. Skeletal muscle is attached to the skeleton and is voluntary. This means that it can be controlled by our conscious thoughts, unlike involuntary muscles.
| Characteristics | Values |
|---|---|
| Type | Involuntary |
| Location | Heart |
| Sub-types | Atrial muscle, Ventricular muscle, Specialised excitatory and conductive muscle fibres |
| Myogenic | Yes |
| Striated | Yes |
| Contraction | Powerful and without tiring |
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What You'll Learn
Cardiac muscle is involuntary
There are three types of muscles in the body: smooth muscle, cardiac muscle, and skeletal muscle. Smooth muscle, which is found in the internal organs and blood vessels, and cardiac muscle, which is found only in the heart, are both involuntary muscles. This means that they are not under our conscious control, and we cannot make them contract through conscious thought.
Cardiac muscle is myogenic, meaning that the muscle fibres can stimulate contractions without needing input from nerve impulses. This is in contrast to voluntary muscles, which are under our conscious control and allow for skeletal movement.
Cardiac muscle is striated, with the bundles of muscle fibres connected at branching, irregular angles called intercalated discs. This is in contrast to skeletal muscle, which is also striated but is arranged in regular, parallel bundles. Striated muscle, including cardiac and skeletal muscle, contracts and relaxes in short, intense bursts, while smooth muscle sustains longer or near-permanent contractions.
The cardiac muscle of the heart can be divided into three subtypes: atrial muscle, ventricular muscle, and specialised excitatory and conductive muscle fibres.
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Cardiac muscle is striated
Cardiac muscle, also known as myocardium or heart muscle, is one of three types of muscle tissues found in the body, the other two being skeletal muscle and smooth muscle. Cardiac muscle forms the contractile walls of the heart, constituting the main tissue of the heart wall. The heart wall is a three-layered structure, with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
Cardiac muscle cells, also known as cardiomyocytes, are the contractile cells of the cardiac muscle. When viewed under a microscope, these cells appear striated or striped, similar to skeletal muscle. This striated appearance is due to the regular arrangement of myofibrils, which are composed of the contractile proteins actin and myosin. The lighter I bands are composed mainly of actin, while the darker A bands are composed primarily of myosin. Unlike skeletal muscle fibres, cardiomyocytes are single cells with a single, centrally located nucleus.
The sheets of cardiac muscle cells wrap around the left ventricle, contracting in a coordinated manner to allow the ventricle to squeeze in multiple directions simultaneously. This includes a longitudinal shortening from apex to base, a radial narrowing from side to side, and a twisting motion similar to wringing out a damp cloth. This complex contraction mechanism allows the heart to squeeze the maximum possible amount of blood out with each heartbeat.
Cardiac muscle cells are joined end-to-end by intercalated discs, forming long cardiac muscle fibres. These intercalated discs contain both anchoring junctions and gap junctions, allowing adjacent cells to synchronise their actions. The regular contraction of cardiac muscle is essential for pumping blood through the body and is under involuntary control.
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Cardiac muscle is found only in the heart
The human body has three major categories of muscles: cardiac muscle, smooth muscle, and skeletal muscle. Cardiac muscle, also called myocardium or heart muscle, is found only in the heart. It is an involuntary, striated muscle that constitutes the main tissue of the heart wall.
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 between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium, which forms the inner lining of the heart chambers and valves, is not cardiac muscle but is instead made up of simple squamous epithelial cells.
Cardiac muscle cells, also called cardiomyocytes, are the contractile myocytes of the cardiac muscle. They 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, specialized ion channels that skeletal muscle does not possess. The calcium channels play an important role in excitation-contraction coupling, which causes the cell's myofilaments to slide past each other, leading to the contraction of the myocardium.
The individual cardiomyocytes are joined by intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously, enabling the heart to work as a pump. The coordinated contractions of the sheets of muscle that wrap around the ventricles allow the ventricles to squeeze in several directions simultaneously, maximising the amount of blood squeezed out of the heart with each heartbeat.
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Skeletal muscle is voluntary
The human body has three types of muscles: smooth muscle, cardiac muscle, and skeletal muscle. Smooth and cardiac muscles are involuntary, while skeletal muscles are voluntary.
Skeletal muscle is found throughout the body, attached to bones via tendons. They are also present in the tongue, diaphragm, eye socket, and upper oesophagus. Skeletal muscles are under our conscious control, meaning we can move them when we want to. These are the muscles we use to make all the movements needed in physical activity and sports. Skeletal muscles serve many purposes, including producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints.
From a mechanical standpoint, the primary function of skeletal muscle is to convert chemical energy into mechanical energy, thus generating force and power. Skeletal muscles are composed of striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and many centimetres long. The nuclei are located in the cell's periphery, adjacent to the sarcolemma, which is a tubular sheath that encases and defines each muscle fibre.
Each muscle fibre is composed of several hundred to several thousand myofibrils, which are made up of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance and creates functional units called sarcomeres. Skeletal muscle comprises approximately 40% of the human body weight and contains 50 to 75% of all body proteins.
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Smooth muscle is involuntary
Smooth muscle is one of the three major types of vertebrate muscle tissue, the other two being skeletal and cardiac muscle. Smooth muscle is involuntary, meaning it is not under our conscious control. We cannot make it contract when we think about it. Smooth muscle is found in the walls of most internal organs, including the stomach, intestines, bladder, and uterus, as well as in the urinary, cardiovascular, gastrointestinal, respiratory, and reproductive systems. It is also present in the skin and eyes.
Smooth muscle differs from skeletal muscle in structure and function. It is non-striated, meaning it has no sarcomeres and therefore no bands or stripes. It consists of thick and thin filaments that do not arrange into sarcomeres, resulting in a non-striated pattern. On microscopic examination, it appears homogeneous. Smooth muscle has greater elastic properties than skeletal muscle, which is important for maintaining contractile tone in certain organ systems, such as the urinary bladder.
At the cellular level, smooth muscle contains large amounts of the proteins actin and myosin, which are responsible for muscle contraction. Actin filaments attach to dense bodies spread throughout the cell, which can be observed under an electron microscope and appear dark. Another important structure is the calcium-containing sarcoplasmic reticulum, which aids in sustaining contraction. Smooth muscle can be divided into two subgroups: single-unit and multi-unit. Single-unit smooth muscle, also known as visceral smooth muscle, makes up most of the smooth muscle in the body. It is found in the walls of internal organs and lines blood vessels, except for large elastic arteries. Multi-unit smooth muscle, on the other hand, is found in the trachea, the iris of the eye, and lining the large elastic arteries.
The primary function of smooth muscle is contraction. In the gastrointestinal tract, it helps with the propulsion of food. In the cardiovascular system, it regulates blood flow and pressure. In the urinary system, it aids in toxin removal and electrolyte balance. In the respiratory system, it is involved in lung function and oxygenation. Smooth muscle also plays a role in the reproductive system, with uterine muscles contracting during childbirth. Overall, smooth muscle is essential for maintaining the body's basic functions.
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Frequently asked questions
No, cardiac muscles are not voluntary. They are found only in the heart and are involuntary muscles.
Involuntary muscles are not under our conscious control, meaning we cannot make them contract when we think about it.
Voluntary muscles are under our conscious control, so we can move them when we want to. They are responsible for causing movements of the skeleton at joints.
There are three types of muscles in the body: smooth muscle, cardiac muscle, and skeletal muscle. Smooth and cardiac muscles are involuntary, while skeletal muscles are voluntary.
