Dominic Stone
The human body is made up of three types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscles are attached to the bones and allow us to perform a wide range of movements. They are also known as striated muscles due to their striped appearance. This striated appearance is caused by the presence of repeating bands of the proteins actin and myosin, which are present along the length of myofibrils. Skeletal muscles are under voluntary control, meaning we can control how and when they move.
| Characteristics | Values |
|---|---|
| Types | Skeletal, cardiac, and smooth muscle |
| Appearance | Striped or striated |
| Muscle Tissue | Skeletal muscle tissue forms skeletal muscles |
| Muscle Fibers | Skeletal muscle fibers are crossed with a regular pattern of fine red and white lines |
| Contraction | Skeletal muscle contraction leads to movement of bones |
| Sarcomeres | Sarcomeres are the functional units of skeletal muscle |
| Myofibrils | Myofibrils are composed of smaller structures called myofilaments |
| Filaments | Thick and thin filaments are composed of proteins |
| Thick Filaments | Thick filaments are composed of the protein myosin |
| Thin Filaments | The primary component of thin filaments is the actin protein |
| Functions | Skeletal muscle helps in maintaining posture, locomotion, and any movement that can be consciously controlled |
| Skeletal Muscle Mass | Skeletal muscles comprise 30% to 40% of total body mass |
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What You'll Learn
Skeletal muscle is voluntary and striated
Skeletal muscle is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones and allow us to perform a wide range of movements and functions. For example, skeletal muscles are used to breathe, eat, and move our bones.
Skeletal muscles are voluntary, meaning we control how and when they move and work. Nerves in our somatic nervous system send signals to make them function. For instance, when reaching for a book on a shelf, we use skeletal muscles in our neck, arm, and shoulder.
Skeletal muscles are also striated, or striped, in appearance. Under a microscope, repeating functional units called sarcomeres are visible along muscle fibres, giving a striated appearance to the tissue. Skeletal muscle fibres contain actin and myosin filaments that power contraction and are organised into these repeating sarcomeres.
The other two types of muscles in the body are cardiac and smooth muscle. Unlike skeletal muscles, cardiac and smooth muscles are involuntary, meaning their movement is not under our conscious control. Cardiac muscles, found in the walls of the heart, are also striated. Smooth muscles, on the other hand, are found in the walls of hollow visceral organs such as the liver, pancreas, and intestines, and do not have a striated appearance due to the lack of sarcomeres.
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Cardiac muscle is involuntary and striated
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are attached to the bones and allow us to perform a wide range of movements and functions. They are also known as striated muscles due to their striped appearance under a microscope.
Cardiac muscle, also called the myocardium, is one of the three major categories of muscles. Cardiac muscle cells are located in the walls of the heart and are under involuntary control. This means that their movement and function are not under our conscious control. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac action potential lasts approximately 200 ms and is divided into five phases: resting, upstroke, early repolarization, plateau, and final repolarization.
Cardiac muscle is also striated, which means it has a striped appearance similar to skeletal muscle. This striated appearance is due to repeating functional units called sarcomeres, which are visible along muscle fibres under a microscope. The sarcomeres consist of thick (myosin) and thin (actin) filaments, which interact to form the basis of the sliding filament theory. The sarcolemma is the cardiomyocyte plasma membrane containing transverse tubules (t-tubules) that play a role in excitation-contraction coupling (ECC), action potential initiation and regulation, maintaining resting membrane potential, and signal transduction.
In summary, cardiac muscle is involuntary and striated. Its striated appearance is due to the presence of sarcomeres, which are responsible for the contractility of the heart and the pumping action that circulates blood throughout the body.
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Smooth muscle is involuntary and not striated
Smooth muscle is one of the three major types of muscle tissue, the other two being skeletal muscle and cardiac muscle. Smooth muscle is found throughout the body and serves a variety of functions. It is present in the stomach, intestines, urinary system, and throughout arteries and veins. In the skin, smooth muscle cells cause hair to stand erect in response to cold temperatures and fear.
Smooth muscle is involuntary, meaning it is controlled by the autonomic nervous system without conscious thought. The nervous system uses hormones, neurotransmitters, and other receptors to control smooth muscle. Smooth muscle is also non-striated, meaning it has no sarcomeres and therefore no stripes. It has greater elastic properties than striated muscle, which is important for maintaining contractile tone in organs like the urinary bladder.
Smooth muscle fibres are located in the walls of hollow visceral organs, such as the liver, pancreas, and intestines, and appear spindle-shaped. They are also found in the walls of blood vessels and lymph vessels, excluding blood and lymph capillaries. In the walls of blood vessels, smooth muscle is known as vascular smooth muscle and plays a vital role in regulating blood pressure and tissue oxygenation.
Smooth muscle can be divided into two subgroups: single-unit and multi-unit smooth muscle. Most smooth muscle is of the single-unit type, found in the walls of most internal organs, blood vessels, the urinary tract, and the digestive tract. In single-unit smooth muscle, a single cell in a bundle is innervated by an autonomic nerve fibre. An action potential can be propagated through neighbouring muscle cells due to the presence of many gap junctions between the cells.
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Skeletal muscle is the most common muscle type
Skeletal muscles are voluntary muscles, meaning that an individual can control how and when they move and work. They are attached to the bones by tendons, which are tough connective tissues. Examples of skeletal muscles include shoulder, hamstring, and abdominal muscles.
Skeletal muscles are composed of muscle fibres, blood vessels, nerve fibres, and connective tissue. Each muscle can contain thousands of fibres, and each fibre is surrounded by a type of connective tissue layer called fascia. The outermost layer of tissue surrounding the entire muscle is called the epimysium, the middle layer surrounding bundles of muscle fibres is the perimysium, and the innermost layer surrounding individual muscle fibres is the endomysium.
The two most significant myofilaments in skeletal muscles are actin and myosin filaments, which are arranged to form various bands on the skeletal muscle. Skeletal muscles have two physiological responses: relaxation and contraction. The contraction of skeletal muscles leads to the movement of the bones to which they are attached, enabling specific movements. Skeletal muscles also provide structural support and help maintain the posture of the body.
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Skeletal muscle is long and cylindrical
Skeletal muscles are long and cylindrical in appearance. They comprise 30% to 40% of the human body's total mass and are attached to the bones, allowing for a wide range of movements and functions. They are also known as striated muscles due to their striped appearance when viewed under a microscope. This striated appearance is caused by repeating bands of the contractile proteins actin and myosin, which are present along the length of myofibrils. These proteins interact with each other for muscle contraction.
Myofibrils are composed of smaller structures called myofilaments, which come in two types: thick filaments and thin filaments. Thick filaments are about 10 nm wide and 1.5 µm long and consist of myosin, while thin filaments are primarily made of actin, measuring 5 nm wide and 2.0 µm long. The thick and thin filaments overlap, creating a dense appearance due to the minimal space between them. The thin filaments attach to a protein in the Z disc, called alpha-actinin, and extend from the Z band to the edge of the H band.
The Z disc, or Z line, is a dense line that runs vertically through the middle of the I band. It marks the border of the functional units of skeletal muscle called sarcomeres. Sarcomeres are responsible for the striated appearance of skeletal muscles, as they are the repeating functional units visible along the muscle fibres. Each sarcomere consists of a space between two consecutive Z discs and contains one entire A band and two halves of an I band. The A bands are dark, while the I bands are light, creating an alternating pattern that gives rise to the striated appearance.
The skeletal muscle is wrapped in epimysium, providing structural integrity during contractions. The perimysium organises the muscle fibres, which are encased in collagen and endomysium, into fascicles. Each muscle fibre contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The release of calcium ions from the sarcoplasmic reticulum is essential for muscle contraction.
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Frequently asked questions
Skeletal muscle, also known as striated muscle, has a stripe-like appearance.
The stripes are caused by repeating bands of the proteins actin and myosin that are present along the length of myofibrils.
Shoulder muscles, hamstring muscles and abdominal muscles are all examples of skeletal muscles.
