Victor Forge
The human body has more than 600 muscles, which make up around half of a person's body weight. These muscles are made of thousands of small fibres woven together, allowing us to do everything from moving our bodies to breathing and staying alive. The muscular system is responsible for the movement of the human body, and there are three types of muscle tissue: visceral, cardiac, and skeletal. Skeletal muscles are the most common type of muscle in the body, comprising 30-40% of total body mass. They are attached to the bones of the skeletal system and allow us to perform a wide range of movements and functions. The individual bundles of muscle fibres in a skeletal muscle are known as fasciculi, and the outermost connective tissue sheath surrounding the muscle is called the epimysium. When looking at meat, the fascicle organisation is visible as the grain of the muscle.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600-700 |
| Percentage of total body mass | 30-40% |
| Types of muscle tissue | Visceral, cardiac, skeletal |
| Skeletal muscle composition | Muscle tissue, blood vessels, tendons, nerves |
| Skeletal muscle function | Voluntary |
| Skeletal muscle movement | Contraction of muscle fibres |
| Skeletal muscle structure | Individual bundles of muscle fibres known as fasciculi |
| Connective tissue sheath covering each fasciculus | Perimysium |
| Connective tissue sheath covering each muscle fibre | Endomysium |
| Connective tissue sheath outermost layer | Epimysium |
| Muscle fibre composition | Actin and myosin filaments |
| Muscle fibre structure | Actin and myosin molecules layered in a repeating pattern to form sarcomeres |
| Sarcomere structure | H zone, M line, I band |
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Skeletal muscle
The human body has over 600 muscles, which are tissues that help the body move and stay alive. There are three types of muscle tissue: visceral, cardiac, and skeletal. Visceral muscle is found inside organs like the stomach, intestines, and blood vessels, while cardiac muscle is only found in the heart. Skeletal muscle, on the other hand, is found throughout the body and is responsible for voluntary movements. Each skeletal muscle is an organ that consists of skeletal muscle tissue, connective tissue, nerve tissue, and blood or vascular tissue. These muscles vary in size, shape, and arrangement of fibres, with some being broad and others narrow.
At the microscopic level, skeletal muscle is composed of numerous cells that fuse together to form a single membrane-bound entity. These fibres run the entire length of a muscle, with the centre filled with structures called myofibrils. Each myofibril is composed of repeating units known as sarcomeres, which consist of myosin and actin molecules layered in a specific way. The arrangement of protein fibres inside the cells causes light and dark bands to appear, indicating that the muscle cell is strong.
The primary artery supplying blood to a skeletal muscle runs parallel to the longitudinal axis of the muscle fibre. This artery gives off tributaries called feed arteries, which run perpendicularly and provide blood to the external connective tissue sheath of the muscle fibre. Skeletal muscles have an abundant supply of blood vessels and nerves, which is essential for their primary function of contraction. Before a skeletal muscle fibre can contract, it must receive an impulse from a nerve cell.
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Cardiac muscle
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The coordinated contraction of the cardiac muscle involves electrical impulses and action potentials that spread from one cell to the next in a phenomenon known as electrical coupling. This rapid, involuntary contraction and relaxation of the cardiac muscle are vital for pumping blood throughout the cardiovascular system.
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Smooth muscle
The understanding of smooth muscle anatomy, physiology, and function is a relatively elusive topic, despite significant research efforts. As our understanding of smooth muscle improves, so too will our ability to treat the pathophysiology associated with its dysfunction.
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Muscle fibre composition
Slow-twitch fibres are associated with endurance, while fast-twitch fibres are associated with power and strength. People who excel at endurance sports tend to have a higher number of slow-twitch fibres, while those who are better at sprint events tend to have more fast-twitch fibres. Training can influence both types of fibres. Sprint training can improve the power generated by slow-twitch fibres, and endurance training can increase the endurance level of fast-twitch fibres. However, training cannot change the inherent characteristics of the fibres. Age-related muscle loss is primarily due to a decrease in both type I and type II fibres, with a higher proportion of type II fibre atrophy.
Muscle fibres can adapt to changing demands by altering their size or composition. This plasticity forms the basis for physical therapy interventions aimed at improving a patient's force development or endurance. Changes in fibre composition may also contribute to impairments and disabilities resulting from prolonged inactivity, limb immobilization, or muscle denervation. The composition of muscle fibre types is influenced by both genetic and environmental factors. In fish, for instance, cold water demands a more efficient muscle metabolism and fatigue resistance, while tropical environments favour fast and powerful movements.
Muscle fibres are composed of thousands of small fibres woven together, with each fibre surrounded by a layer of connective tissue called the endomysium. Numerous fibres are bundled into groups called fascicles, which are sheathed in connective tissue known as the perimysium. The fascicle organisation is what gives meat its "grain." Skeletal muscles are named based on various factors, including location, origin, insertion, shape, and function. They are attached to bones via tendons, allowing for skeletal movement. Skeletal muscle fibres must have a nerve fibre attached to them to function, and they can be classified based on contraction speed and ATP regeneration.
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Muscle movement
Muscles are tissue, composed of specialised cells known as muscle cells or myocytes. Myocytes are characterised by protein filaments known as actin and myosin. These filaments slide past one another, producing contractions that move body parts, including internal organs. Each muscle is made up of groups of muscle fibres called fascicles, surrounded by a layer of connective tissue called perimysium. Each fascicle is made up of thousands of fibres woven together, and each fibre is surrounded by another layer of connective tissue called endomysium.
The actin and myosin molecules are layered in a specific way, with actin molecules attached to the adjacent sarcomere at a structure called the Z line. The sarcomere is the fundamental contractile unit of a skeletal muscle. The actin molecules are between three myosin molecules, and each myosin is surrounded by six actin molecules. As the actin molecules ratchet towards each other along the myosin molecule, the sarcomere shortens, resulting in the macroscopic shortening of the muscle. The H zone, which is the lighter area in the centre of the sarcomere, gets smaller as the muscle contracts and larger as it lengthens.
There are three types of muscles in the body: skeletal, cardiac, and smooth. Skeletal muscles are voluntary muscles, meaning we have conscious control over them. They are attached to the bones of the skeletal system and allow us to perform a wide range of movements. Cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system. Cardiac muscle is only found in the heart, while smooth muscle is present in the head and neck, surrounding blood vessels, and within the eyes.
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Frequently asked questions
Muscles are tissue, made up of thousands of small fibres woven together. They are responsible for the movement of the human body.
There are over 600 muscles in the human body. They make up around 30-40% of a person's body weight.
There are three types of muscle: skeletal, cardiac, and smooth. Skeletal muscles are voluntary, meaning you control how and when they move. Cardiac and smooth muscle are involuntary.
Skeletal muscles are attached to the bones of the skeletal system. They are the most common type of muscle in the body and are responsible for a wide range of movements and functions.
The grain of a muscle refers to the fascicles, or bundles of muscle fibres. These are the individual bundles of muscle fibres in a skeletal muscle.
