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Muscles are pieces of soft tissue that help the body move, breathe, swallow, pump blood, and stay alive. There are about 600 muscles in the human body, and they are made of thousands of small fibres woven together. These fibres are composed of proteins called actin and myosin, which interact to cause movement. The body mass of an average adult man is made up of 42% skeletal muscle, while an average adult woman is made up of 36%.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600 |
| Muscle composition | Tissue, blood vessels, lymphatics, contractile muscle fibres, and connective tissue sheaths |
| Muscle fibre composition | Blocks of proteins called myofibrils, which contain a specialised protein (myoglobin) and molecules to provide the oxygen and energy required for muscle contraction |
| Muscle fibre shape | Flat, triangular, or circular |
| Types of muscle tissue | Skeletal muscle, cardiac muscle, and smooth muscle |
| Skeletal muscle composition | Actin, myosin, tendons, and perimysium |
| Smooth muscle composition | Actin, myosin, and thick and thin filaments |
| Cardiac muscle composition | Actin, myosin, and sarcomeres |
| Muscle fibre types | Type I (slow oxidative fibres), Type IIa (fast oxidative fibres), and Type IIb (fast glycolytic fibres) |
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What You'll Learn
Muscle fibres are made of proteins
Muscles are pieces of soft tissue that help the body move, breathe, swallow, and stay alive. There are over 600 muscles in the human body, and they are constantly being used, whether consciously or unconsciously. For example, the heart is a muscle that beats thousands of times a day to keep us alive.
Each muscle is made up of thousands of small fibres woven together. These fibres stretch and press together to enable movement. Skeletal muscle is made up of opposing pairs of muscles, such as the biceps and triceps, and they are under conscious control. Smooth muscle, on the other hand, is located in the digestive tract, uterus, and blood vessels, and its movement is involuntary. Cardiac muscle is specific to the heart and also moves involuntarily. Despite their different functions, all three types of muscle share the same basic composition.
The structure of muscle fibres is influenced by the substances in the cytoplasm, as they do not have a surface membrane. The transverse striations of the fibrils of the muscle fibre are due to a difference in density. These cross-striations form a pattern that repeats along the whole length of the fibre, with each repeating part known as a "
The number of muscle fibres cannot be increased through exercise. Instead, muscles grow larger through a combination of muscle cell growth and the addition of new protein filaments. To build and maintain muscle mass, a daily protein intake of 1.4-2.0 g protein/kg body weight/day is recommended for people who are physically active.
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Muscles are made of thousands of fibres
The human body has about 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. There are three types of muscle tissue: skeletal, cardiac, and smooth muscle.
Skeletal muscle is the specialised tissue that is attached to bones and allows movement. It is under our conscious control and is also known as voluntary muscle. When viewed under a microscope, the tissue looks striped or striated. Skeletal muscle is found throughout the body and functions to contract in response to a stimulus. Skeletal muscle comprises approximately 40% of the human body weight and contains 50 to 75% of all body proteins.
Cardiac muscle tissue is found only in the walls of the heart as myocardium, and it is an involuntary muscle controlled by the autonomic nervous system. Cardiac muscle tissue is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles. Cardiac muscle connects at branching, irregular angles known as intercalated discs.
Smooth muscle is located in various internal structures, including the digestive tract, uterus, and blood vessels such as arteries. It is arranged in layered sheets that contract in waves along the length of the structure. Smooth muscle is also known as involuntary muscle, as its motion happens without our conscious awareness.
All three types of muscle tissue have the same basic composition, which includes contractile proteins called actin and myosin that interact to cause movement. Actin and myosin are the two most essential myofilaments that make up the contractile elements of the muscle fibre. Each muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein called myoglobin and molecules to provide the oxygen and energy required for muscle contraction.
A typical muscle is serviced by anywhere between 50 and 200 (or more) branches of specialised nerve cells called motor neurones. These plug directly into the skeletal muscle. The outermost sheath of connective tissue covering each muscle is called the epimysium. Each muscle is made up of groups of muscle fibres called fascicles, surrounded by a connective tissue layer called the perimysium. Multiple units of individual muscle fibres within each fascicle are surrounded by endomysium, a connective tissue sheath.
Muscles are made of thousands of these fibres, bundled tightly together. They are woven together and stretch and press together to move our organs and body.
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Muscle fibres are grouped into fascicles
The human body is made up of about 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. Muscles work by contracting or relaxing, and they derive their energy from glucose and other dietary substances such as calcium, magnesium, potassium, and sodium.
Each muscle is made up of thousands of elastic muscle fibres bundled tightly together. These fibres are composed of blocks of proteins called myofibrils, which contain a specialized protein called myoglobin, as well as molecules to provide the oxygen and energy required for muscle contraction. Each myofibril contains filaments that fold together when given the signal to contract, shortening the length of the muscle fibre and, in turn, the entire muscle.
The two most essential myofilaments that make up the contractile elements of the muscle fibre are actin and myosin, which interact to cause movement. Actin is a thin filament, while myosin is a thick filament. These two proteins give skeletal muscle its microscopic striated appearance and create functional units called sarcomeres, which are bordered by a Z-line. The Z-line serves as the site of origin for the thin actin filaments, which project towards each other as they partially overlap the myosin filaments.
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Muscles are made of different types of tissue
There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscles are attached to bones and allow movement. They are under our conscious control and are also known as voluntary muscles. They are made of elongated, multinucleate muscle cells called muscle fibres. These fibres are composed of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of these filaments gives skeletal muscle its microscopic striated appearance.
Cardiac muscle tissue is found only in the walls of the heart as myocardium. It is an involuntary muscle controlled by the autonomic nervous system. Cardiac muscle tissue is striated, containing sarcomeres in highly regular arrangements of bundles. Smooth muscle, on the other hand, is non-striated and involuntary. It is found within the walls of organs and structures such as the oesophagus, stomach, intestines, and blood vessels. Smooth muscle fibres are spindle-shaped organs with a single nucleus. They also contain actin and myosin contractile proteins, as well as thick and thin filaments.
In addition to these three main types, there are also ligaments, which are a tougher form of muscle that connects to other muscles on both ends. Furthermore, muscles are classified based on their shape, such as flat, triangular, and circular muscles.
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Muscle fibres are formed during embryogenesis
The development of skeletal muscles in the limbs and trunk depends on the expression of MyoD and Myf5, which are influenced by signalling molecules like Wnt and BMP. These embryonic myoblasts further differentiate to form primary muscle fibres and eventually secondary myofibers through the union of myoblasts in the fetus.
The formation of skeletal muscle fibres involves the fusion of myoblasts, resulting in muscle fibres with multiple nuclei. Myoblasts that do not form muscle fibres dedifferentiate into satellite cells, which remain adjacent to muscle fibres and can differentiate and fuse to augment or form new muscle fibres.
The skeletal muscle fibres are composed of thousands of individual muscle fibres wrapped together by connective tissue sheaths. These muscle fibres, also known as myocytes or myofibrils, contain myofilaments like actin and myosin that play a crucial role in muscle contraction. The arrangement of these myofibrils gives rise to the striated appearance of skeletal muscles.
Overall, the formation of muscle fibres during embryogenesis involves a complex process of differentiation, migration, and fusion of various cell types, ultimately resulting in the skeletal muscles that enable movement and support vital functions in the body.
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Frequently asked questions
Muscles are made from thousands of elastic fibres bundled tightly together. These fibres are composed of proteins called actin and myosin, which are responsible for muscle contraction.
There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that we can control consciously. Smooth and cardiac muscles contract involuntarily without conscious intervention.
Muscles have a range of functions, from pumping blood and supporting movement to lifting heavy weights or giving birth. They also help to maintain posture and balance.
Muscles work by contracting or relaxing to cause movement. This movement may be voluntary or involuntary. Contraction occurs when muscle fibres receive a signal to contract, causing them to fold together and shorten.
