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Striated muscle tissue, also known as skeletal muscle, is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. It is a highly organised tissue that converts chemical energy to physical energy, allowing for movement and support of the bones. Skeletal muscles are attached to the bones by tendons and are under voluntary control, meaning they move when the brain sends signals in the form of nerve impulses. They are composed of densely packed myofibrils, which give them their characteristic striped appearance under a microscope.
| Characteristics | Values |
|---|---|
| Types | Skeletal, cardiac, and smooth muscle |
| Appearance under a microscope | Striated or striped structure with dark and light alternate striations or bands |
| Tissue | Highly organized tissue that helps in the conversion of chemical energy to physical energy |
| Function | To generate force and contract to support respiration, locomotion, posture, and pumping of blood throughout the body |
| Contraction | Due to the ATP-dependent rowing motion of the myosin heads causing a shift of the actin filaments |
| Skeletal muscle fibres | Flexible muscle fibres that range from less than 0.5 inches to over 3 inches in diameter |
| Control | Skeletal muscles are voluntary muscles, while cardiac and smooth muscles are involuntary |
| Nerves | Skeletal muscles are controlled by the somatic nervous system, while cardiac and smooth muscles are controlled by the autonomic nervous system |
| Muscle mass | Skeletal muscles comprise 30% to 40% of total body mass |
| Muscle fibres | Skeletal muscle fibres are red and white |
| Connective tissue | Skeletal muscles are attached to bones by collagen-rich tendons |
| Muscle cells | Skeletal muscle cells have many nuclei, while cardiac and smooth muscle cells have a single nucleus |
| Muscle regeneration | Skeletal muscles can regenerate better than cardiac muscles due to satellite cells |
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What You'll Learn
Skeletal muscle vs. cardiac muscle
Striated musculature comprises two types of tissues: skeletal muscle and cardiac muscle. Skeletal muscle is the most common type of muscle in the human body, accounting for 30% to 40% of total body mass. These muscles are attached to the bones and allow for a wide range of movements and functions. They are voluntary muscles, meaning an individual can control how and when they move. For example, when reaching for a book on a shelf, one uses skeletal muscles in their neck, arm, and shoulder.
Skeletal muscle fibres are around 20-100 µm thick and up to 20 cm long, and each muscle can contain thousands of fibres. The fibres contract, allowing the muscles to move bones. Skeletal muscles are also involved in breathing, posture maintenance, and stabilizing the skeleton. They are innervated by the somatic nervous system, which allows for voluntary control. Additionally, skeletal muscles have superior regenerative abilities compared to cardiac muscles due to the presence of satellite cells.
Cardiac muscle, on the other hand, is found only in the walls of the heart. These muscles are responsible for the heart's contraction and pumping blood throughout the body. Cardiac muscle cells are smaller, typically measuring 10-20 µm in thickness and 50-100 µm in length. They have a single, centrally located nucleus, and are connected by intercalated discs that provide both mechanical and electrical coupling. Cardiac muscle contractions are involuntary and are controlled by the autonomic nervous system. The contractions result from the ATP-dependent movement of myosin heads, which cause a shift in the actin filaments.
Both skeletal and cardiac muscles have a striated appearance under a microscope due to their densely packed myofibrils. However, they differ in their histology and physiology. Skeletal muscles have multiple nuclei, while cardiac muscles typically have a single nucleus. Additionally, cardiac muscles have a more complex arrangement of fibrils, which do not run strictly parallel but rather branch out.
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How striated muscles work
Striated muscle tissue is responsible for the voluntary movements of bones. It comprises two types of tissues: skeletal muscle and cardiac muscle. Skeletal muscle is the most common type of muscle in the human body, accounting for 30-40% of total body mass. It is attached to the bones by collagen-rich tendons and is made up of muscle fibres and connective tissue layers. Skeletal muscle fibres are red and white, ranging from less than half an inch to just over 3 inches in diameter. They contract, enabling breathing, movement and posture maintenance.
Cardiac muscle, on the other hand, is found on the walls of the heart. Its main task is heart contraction, which pumps blood throughout the body. Cardiac muscle cells are smaller than skeletal muscle cells, and they have a single nucleus located centrally. Cardiac muscle cells are connected by intercalated discs, which facilitate mechanical and electrical connections.
The fibres of striated muscle have a cylindrical shape with blunt ends. Under a microscope, striated muscles have a distinct appearance due to their densely packed myofibrils. The functional unit of a muscle fibre is called a sarcomere, which consists of actin and myosin myofilaments. The actin filaments are attached to the Z-line, found in the middle of the I-bands, and the myosin filaments are anchored in the centre of the A-bands. The contraction of the muscle occurs when the myosin heads exhibit an ATP-dependent rowing motion, causing a shift of the actin filaments.
Skeletal muscle can be classified as slow-oxidative (Type I) or fast-oxidative (Type II) based on their contractile and metabolic phenotypes. Additionally, skeletal muscle has a superior regenerative capacity compared to cardiac muscle due to the presence of satellite cells.
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The structure of striated muscles
Skeletal muscle is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. These muscles connect to bones and allow for a wide range of movements and functions. Skeletal muscles are voluntary, meaning individuals control how and when they work. Skeletal muscle fibres are typically 20-100 µm thick and up to 20 cm long. They are surrounded by endomysium, forming the primary bundle, which is the functional unit of the muscle. Groups of these primary bundles are wrapped by the perimysium, forming secondary bundles. The entire skeletal muscle is enclosed by epimysium, a connective tissue that maintains structural integrity during contractions.
Cardiac muscle, on the other hand, is found only in the heart. These muscles are responsible for heart contractions and pumping blood throughout the body. Cardiac muscle cells have a single, centrally located nucleus and are smaller than skeletal muscle cells, measuring 10-20 µm in thickness and 50-100 µm in length. The structure of the sarcomere in cardiac muscle resembles that of skeletal muscle, but with larger T-tubules and a smaller L-system. Cardiac muscle cells are connected by intercalated discs, which provide mechanical and electrical coupling.
Both skeletal and cardiac muscles have a striated appearance due to their densely packed myofibrils. Skeletal muscle fibres are composed of actin and myosin filaments, which interact to produce muscle contractions. Similarly, cardiac muscle contractions are facilitated by the release of calcium ions from the sarcoplasmic reticulum, enabling the movement of myosin and actin filaments.
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Striated muscle regeneration
Striated muscle tissue is a muscle tissue type that features repeating functional units called sarcomeres. Under a microscope, sarcomeres are visible along muscle fibres, giving a striated appearance to the tissue. The two types of striated muscle tissue are skeletal muscle and cardiac muscle. Skeletal muscle is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. These muscles are attached to bones and allow for a wide range of movements and functions. They are voluntary muscles, meaning we control how and when they move.
Cardiac muscle, on the other hand, is found in the walls of the heart. Cardiac muscle cells have a complex structure, with a single, centrally located nucleus and densely packed mitochondria. Cardiac muscle cells are connected to each other by intercalated discs, which facilitate mechanical and electrical connections.
Skeletal muscle has a superior regenerative capacity compared to cardiac muscle due to the presence of satellite cells. These mononucleated quiescent cells are dormant in healthy skeletal muscle tissue. When skeletal muscle is damaged, satellite cells are stimulated to divide and fuse with existing muscle fibres, repairing and regenerating the damaged fibres. The regeneration process can be divided into three phases: the inflammatory response, the activation, differentiation, and fusion of satellite cells, and the maturation and remodelling of newly formed myofibrils.
The inflammatory phase begins with the necrosis of damaged muscle fibres, inducing an inflammatory response. Macrophages play a crucial role in this phase by phagocytosing cell debris and secreting anti-inflammatory cytokines to terminate the inflammation. These macrophages also promote the proliferation and differentiation of satellite cells. The satellite cells re-enter the cell cycle, multiplying before leaving it to self-renew or differentiate into myoblasts.
Regulatory T cells (Treg) are another important cell population involved in muscle regeneration. They regulate the inflammatory infiltrate at the site of tissue damage and influence the behaviour of satellite cells. Studies have shown that Treg-deficient mice exhibit reduced regenerative potential, highlighting the significance of Treg cells in the process.
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Types of muscle tissue
Muscle tissue is a soft tissue that makes up different groups of muscles in the body. These muscles help the body to move, breathe, swallow, and stay alive. There are three major types of muscle tissue in the human body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are attached to bones and help with movement and weight support. They are voluntary muscles, meaning that their movement can be consciously controlled. Skeletal muscles are the most common type of muscle in the body, constituting approximately 30-40% of total body mass. They are also the only type of muscle that can be classified as slow-oxidative (Type I) or fast-oxidative (Type II), depending on their contractile and metabolic phenotypes.
Cardiac muscle, on the other hand, is found only in the heart. Its main task is to contract the heart and pump blood throughout the body. Cardiac muscle cells are unicellular and contain many mitochondria and myoglobin. They are connected to each other by intercalated discs, which allow for rapid electrical transmission and contraction as a single unit. Cardiac muscle is an involuntary muscle, meaning its movement cannot be consciously controlled.
Smooth muscle is the third type of muscle tissue and is found in hollow structures such as the walls of the intestines, blood vessels, and other organs. Unlike skeletal and cardiac muscle tissue, smooth muscle tissue is not striated because it does not contain sarcomeres.
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Frequently asked questions
Stratified muscles, also known as striated muscles, are a type of muscle tissue that features repeating functional units called sarcomeres. They are called stratified muscles because, under a microscope, they appear to have a striped structure with alternating dark and light bands.
There are two types of stratified muscles: skeletal muscle and cardiac muscle. Skeletal muscles are attached to bones and are under voluntary control, whereas cardiac muscles are found in the heart and are involuntary.
Under a microscope, stratified muscles exhibit a highly ordered ultrastructure consisting of sarcomeres, which are basic contractile units containing a central myosin-rich dark anisotropic (A) band and two actin-dominated light isotropic (I) bands. The actin filaments are attached to the Z-line found in the middle of the I-bands.
The primary function of stratified muscles is to generate force and
