Dominic Stone
Skeletal muscle is a multinucleated muscle type that is found throughout the body and functions to contract in response to a stimulus. Skeletal muscle serves many purposes, including producing movement, maintaining body posture and position, and stabilizing joints. The multinucleated condition of skeletal muscle fibres results from multiple myoblasts fusing to produce each muscle fibre, with each myoblast contributing a nucleus.
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What You'll Learn
Skeletal muscle cells are multinucleated
The nuclei within skeletal muscle cells, typically positioned at the cell's periphery, are called myonuclei. These nuclei are distributed along the cell to maximise their distance from each other, a crucial arrangement for optimal cell function. This positioning is thought to be influenced by a force balance generated by microtubules, as suggested by computational modelling studies.
Skeletal muscle cells, found throughout the body, play a vital role in various functions, including producing movement, maintaining body posture, and stabilising joints. They also contribute to the body's temperature regulation, nutrient storage, and make up a significant proportion of body weight, accounting for approximately 40% in humans.
The multinucleated structure of skeletal muscle cells is not just a result of cell fusion but also serves a functional purpose. The presence of multiple nuclei allows for the efficient production of the vast amount of proteins required by these cells. This is particularly important given the high metabolic demand of skeletal muscles, which contain 50 to 75% of all body proteins.
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Myoblasts fuse to form multinucleated myotubes
Skeletal muscle is a highly organised tissue composed of bundles of muscle fibres called myofibers. Each myofiber represents a muscle cell with its basic cellular unit, the sarcomere. Skeletal muscle fibres are the only muscle cells that are multinucleated, with the nuclei usually referred to as myonuclei.
Myoblasts are mononucleated muscle precursor cells that fuse together to form multinucleated myotubes. This process is called myogenesis and is a required event for proper skeletal muscle development and regeneration. Myoblasts also fuse to other myotubes during muscle growth and repair. The fusion of myoblasts and myotubes is facilitated by numerous proteins, including two muscle-specific fusion proteins, Myomaker and Myomerger-Minion. Myomaker is required symmetrically (on both fusing cells), whereas Minion/Myomerger is required asymmetrically (only one cell of the pair).
Myotubes are immature, multinucleated muscle cells with nuclei located in the centre. They are long and cylindrical in shape and are formed from the fusion of myoblasts. Myotubes synthesise contractile proteins actin and myosin, as well as other regulatory proteins such as troponin and tropomyosin. These proteins combine to form myofibrils, the muscle fibres.
During the process of maturation, the early mononuclear muscle cells, or myoblasts, fuse to generate multinucleated cells or myotubes, which subsequently differentiate into myofibers. Myofibers are mature multinucleated muscle cells, more commonly known as muscle fibres. They are composed of numerous myofibrils, which are made up of actin (thin filaments) and myosin (thick filaments) arranged in a hexagonal pattern.
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Skeletal muscle fibres are striated
Skeletal muscle is one of the three types of vertebrate muscle tissue, the other two being cardiac and smooth muscle. Skeletal muscle is found throughout the body and is responsible for various functions, including producing movement, maintaining body posture, controlling body temperature, and stabilising joints. It also serves as an endocrine organ and constitutes about 35%-40% of the human body weight.
The multinucleated condition of skeletal muscle fibres results from multiple myoblasts fusing to produce each muscle fibre, with each myoblast contributing a nucleus. These nuclei, termed myonuclei, are located along the inside of the cell membrane, in the cell's periphery, adjacent to the sarcolemma. The sarcolemma, a tubular sheath that encases each muscle fibre, is composed of a plasma membrane and a polysaccharide coating that fuses with tendon fibres. It serves as a major location for ion exchange and receives and conducts stimuli.
The skeletal muscle fibres are composed of myofibrils, which are made up of actin (thin filaments) and myosin (thick filaments) and support proteins. These myofibrils are bundled together to form fascicles, which are then grouped to form a muscle encased by a fibrous tissue envelope called the epimysium. This arrangement provides structural integrity to the muscle despite contractions.
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Skeletal muscle is composed of bundles of muscle fibres
Skeletal muscle is one of the three major muscle tissues in the human body, alongside cardiac and smooth muscle groups. Skeletal muscle is found throughout the body and is responsible for producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints. Skeletal muscle comprises approximately 40% of human body weight and contains 50-75% of all body proteins.
Bundles of myofibers form fascicles, and bundles of fascicles form muscle tissue. Each muscle fibre is a single cylindrical muscle cell, and an individual skeletal muscle may be made up of hundreds or even thousands of muscle fibres bundled together and wrapped in a connective tissue covering. Each muscle is surrounded by a connective tissue sheath called the epimysium, and the individual bundles of muscle fibres within a skeletal muscle are known as fasciculi. The outermost connective tissue sheath surrounding the entire muscle is the epimysium, and the innermost sheath surrounding individual muscle fibres is the endomysium. The connective tissue coverings furnish support and protection for the delicate muscle cells and allow them to withstand the forces of contraction.
Skeletal muscle fibres are multinucleated, with nuclei usually referred to as myonuclei. They are 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. The sarcolemma is a tubular sheath that encases and defines each muscle fibre, forming a barrier between extracellular and intracellular compartments. The sarcolemma is also the site of stimuli reception and conduction.
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Skeletal muscle contraction is mostly under voluntary control
Skeletal muscle, also known as voluntary muscle, is found throughout the body and functions to contract in response to a stimulus. Unlike smooth or cardiac muscle, skeletal muscle contraction is mostly under voluntary control, receiving neural inputs that allow for the conscious control of muscles. Skeletal muscle serves many purposes, including producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints.
Skeletal muscle is a highly organized tissue composed of bundles of muscle fibres called myofibers, which contain several myofibrils. Each myofiber represents a muscle cell with its basic cellular unit, the sarcomere. Bundles of myofibers form fascicles, and bundles of fascicles form muscle tissue. Skeletal muscle fibres are the only muscle cells that are multinucleated, with the nuclei usually referred to as myonuclei. These nuclei are located in the cell's periphery, adjacent to the sarcolemma. The sarcolemma is a tubular sheath that encases and defines each muscle fibre, forming a barrier between extracellular and intracellular compartments.
The sarcolemma is composed of a plasma membrane and a polysaccharide coating that fuses with tendon fibres. Invaginations within the sarcolemma are called transverse tubules (T-tubules), which function as a major location for ion exchange. The sarcoplasmic reticulum serves as a reservoir for calcium ions, so when an action potential spreads over the T-tubule, it signals the sarcoplasmic reticulum to release calcium ions from the gated membrane channels to stimulate muscle contraction.
Striated muscle fibres contain actin and myosin filaments that power contraction and are organized into repeating arrays called sarcomeres, with a striated microscopic appearance. The thin myofilaments are filaments of mostly actin, and the thick filaments are mostly made of myosin. These filaments slide over each other to shorten the fibre length in a muscle contraction. The smallest contractile unit in the fibre is the sarcomere, which is a repeating unit within two Z bands. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance and creates functional units called sarcomeres.
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Frequently asked questions
Skeletal muscle is multinucleated.
Skeletal muscles are a type of muscle found throughout the body that contracts in response to a stimulus. They are responsible for producing movement, maintaining body posture, and storing nutrients, among other functions.
Skeletal muscle fibers are composed of multiple nuclei, which are located in the cell's periphery, adjacent to the sarcolemma. The presence of multiple nuclei is a unique feature of skeletal muscle cells.
