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There are three types of muscle tissue in the body: skeletal, smooth, and cardiac. Smooth muscle, also known as visceral muscle, is found in the walls of internal organs such as the digestive, reproductive, and urinary tracts, as well as tubes like airways and blood vessels. Unlike skeletal muscle, which is under voluntary control, the activities of visceral muscles are not controlled by the nervous system and are therefore involuntary.
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What You'll Learn
Visceral muscles are involuntary
Visceral muscle tissue, also known as smooth muscle, is tissue associated with the internal organs of the body, especially those in the abdominal cavity. Smooth muscle is involuntary, meaning it is not under our conscious control. It gets its name from its lack of a striped appearance under a microscope, unlike skeletal and cardiac muscle. Smooth muscle is found in the walls of hollow organs such as the digestive, reproductive, and urinary tracts, as well as in tubes such as blood vessels and airways.
Smooth muscle is composed of bundles of specialized cells capable of contraction and relaxation to create movement. These contractions occur spontaneously without nervous or hormonal stimulation, and they are responsible for pumping blood throughout the body and maintaining blood pressure. The heart, for example, contracts or beats about 100,000 times per day, 36 million times per year, and about 2.5 billion times over a lifetime.
In contrast, skeletal muscle is under voluntary control, meaning we can consciously control it in response to input by nerve cells. Skeletal muscle is also referred to as striated or "striped" due to its microscopically streaked appearance. It comprises about 40% of our body weight and is found alongside connective tissue.
To summarize, visceral or smooth muscle is involuntary, while skeletal muscle is voluntary. These different types of muscle tissues work together to maintain the body's functions and movements, each playing a crucial role in our overall physiology.
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Smooth muscle is a type of visceral muscle
The activities of visceral muscles are not under the voluntary control of the nervous system. Smooth muscle is sometimes known as visceral muscle because it is a major component of many internal (or visceral) organs. Smooth muscle is widely distributed throughout the body, being found in the walls of hollow organs such as the digestive, reproductive, and urinary tracts, tubes such as blood vessels and airways, and in other locations, such as the stomach, intestines, bladder, and uterus.
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non-striated, meaning it has no sarcomeres and therefore no striations (bands or stripes). Smooth muscle can be further divided into two subgroups: single-unit and multi-unit smooth muscle. Single-unit smooth muscle, also known as visceral smooth muscle, is the most common type observed in the human body. It is found in the walls of most internal organs (viscera) and lines blood vessels (except large elastic arteries), the urinary tract, and the digestive tract.
Single-unit smooth muscle produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body. It contains gap junctions to synchronize membrane depolarization and contractions so that the muscle contracts as a single unit. It has a stress-relaxation response that permits the muscle to stretch, contract, and relax as the organ expands. In single-unit smooth muscle, a single cell in a bundle is innervated by an autonomic nerve fiber (myogenic). An action potential can be propagated through neighboring muscle cells due to the presence of many gap junctions between the cells.
Multi-unit smooth muscle, on the other hand, is composed of cells that rarely possess gap junctions, and thus are not electrically coupled. As a result, contraction does not spread to other cells, but is instead confined to the cell that was originally stimulated. Smooth muscle can be stimulated by pacesetter cells, by the autonomic nervous system, by hormones, spontaneously, or by stretching. Smooth muscle is capable of contracting spontaneously without nervous or hormonal stimulation, and it can also maintain contractions with very little energy expenditure.
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Skeletal muscle is voluntary
Skeletal muscle is one of the three types of muscle tissues in the body, the others being cardiac muscle and smooth muscle. It is also referred to as voluntary muscle because we can consciously control it in response to input by nerve cells. Skeletal muscle, along with cardiac muscle, is also called striated muscle because it has a microscopically streaked or striped appearance. This appearance is due to the arrangement of the sarcomeres, which are functional units created by the arrangement of actin and myosin that give skeletal muscle its striated quality.
Skeletal muscle is found throughout the body and is attached to bones via tendons. It can be found in the tongue, diaphragm, eye socket, and upper oesophagus. The main functions of skeletal muscle are to contract to produce movement, sustain body posture and position, maintain body temperature, store nutrients, and stabilize 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 muscle is 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 composed of actin (thin filaments), myosin (thick filaments), and support proteins.
Skeletal muscle disorders typically manifest as muscle weakness. Multiple types of skeletal muscle disorders have been studied, including muscular dystrophies, congenital myopathies, inflammatory disorders, and diseases affecting the neuromuscular junction.
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Cardiac muscle is also involuntary
The body has three types of muscle tissues: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle is also known as voluntary muscle because we can consciously control it in response to input from nerve cells.
Smooth muscle, on the other hand, is involuntary and is sometimes known as visceral muscle. It is a major component of many internal organs, including the walls of hollow organs such as the digestive, reproductive, and urinary tracts, as well as tubes like blood vessels and airways.
Cardiac muscle, like smooth muscle, is also involuntary. It is the main tissue of the heart wall and is responsible for the heart's pumping action, keeping blood circulating throughout the body. This muscle tissue contracts and releases involuntarily, and its movement is automatic and cannot be controlled by a person.
Cardiac muscle cells, also called cardiomyocytes, are the contractile cells of the cardiac muscle. These cells are highly interconnected and work together in a coordinated manner to pump blood from the heart. The Purkinje fibres rapidly conduct electrical signals, while the coronary arteries bring nutrients to the muscle cells, and veins and a capillary network remove waste products.
The heart also contains specialized types of cardiac tissue, including pacemaker cells, which are weakly contractile and generate electrical impulses that control heart rate and determine how fast the heart pumps blood.
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Visceral muscles line internal organs
There are three types of muscle tissues in the human body: skeletal, smooth, and cardiac. Skeletal muscles are under voluntary control, meaning we can consciously control them in response to input by nerve cells. They are also referred to as striated muscles because they have a microscopically streaked or striped appearance.
Smooth muscles, on the other hand, are involuntary and are not under our conscious control. They are sometimes known as visceral muscles because they are a major component of many internal (or visceral) organs. Smooth muscles are widely distributed throughout the body, found in the walls of hollow organs such as the digestive, reproductive, and urinary tracts, as well as in tubes like blood vessels and airways.
Visceral muscle tissue, or smooth muscle, is associated with the internal organs of the body, especially those in the abdominal cavity. These involuntary muscles line the blood vessels, stomach, digestive tract, and other internal organs. They are composed of bundles of specialized cells capable of contraction and relaxation, creating movement.
The activities of visceral muscles are not under the voluntary control of the nervous system. This means that, unlike skeletal muscles, we cannot consciously control their movement. However, visceral muscles are essential for the functioning of our internal organs, and their involuntary contractions and relaxations help maintain our bodily functions.
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Frequently asked questions
No, visceral muscles are not under the voluntary control of the nervous system.
Visceral muscle tissue, also known as smooth muscle, is associated with the internal organs of the body, especially those in the abdominal cavity.
Smooth muscles are found in the walls of hollow organs such as the digestive, reproductive, and urinary tracts, tubes such as blood vessels and airways, and in other locations such as the stomach and heart.
There are three types of muscle tissues in the body: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscles are voluntary, while cardiac and smooth muscles are involuntary.
Unlike skeletal and cardiac muscles, visceral or smooth muscles do not have a striped appearance when viewed microscopically.
