musculature - traducción al
![(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to [[lactic acid]]. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to [[muscle fatigue]]. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.](https://commons.wikimedia.org/wiki/Special:FilePath/1016 Muscle Metabolism.jpg?width=200 "(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to [[lactic acid]]. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to [[muscle fatigue]]. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.")
![Types of [[pennate muscle]]. A – [[unipennate]]; B – [[bipennate]];
C – [[multipennate]]](https://commons.wikimedia.org/wiki/Special:FilePath/Fiederung.svg?width=200 "Types of [[pennate muscle]]. A – [[unipennate]]; B – [[bipennate]];
C – [[multipennate]]")
![[[Human embryo]] showing [[somite]]s labelled as ''primitive segments''.](https://commons.wikimedia.org/wiki/Special:FilePath/Gray20.png?width=200 "[[Human embryo]] showing [[somite]]s labelled as ''primitive segments''.")
![polypeptide]] tail (only one tail of each pair is shown). The pairs of histones, H2A, H2B, H3 and H4, each have [[lysine]]s (K) in their tails, some of which are subject to post-translational modifications consisting, usually, of acetylations [Ac] and methylations {me}. The lysines (K) are designated with a number showing their position as, for instance, (K4), indicating lysine as the 4th amino acid from the amino (N) end of the tail in the histone protein. The particular acetylations [Ac] and methylations {Me} shown are those that occur on nucleosomes close to, or at, some DNA regions undergoing transcriptional activation of the DNA wrapped around the nucleosome.](https://commons.wikimedia.org/wiki/Special:FilePath/Histone tails set for transcriptional activation.jpg?width=200 "polypeptide]] tail (only one tail of each pair is shown). The pairs of histones, H2A, H2B, H3 and H4, each have [[lysine]]s (K) in their tails, some of which are subject to post-translational modifications consisting, usually, of acetylations [Ac] and methylations {me}. The lysines (K) are designated with a number showing their position as, for instance, (K4), indicating lysine as the 4th amino acid from the amino (N) end of the tail in the histone protein. The particular acetylations [Ac] and methylations {Me} shown are those that occur on nucleosomes close to, or at, some DNA regions undergoing transcriptional activation of the DNA wrapped around the nucleosome.")
![Prisoner of war exhibiting muscle loss as a result of [[malnutrition]].](https://commons.wikimedia.org/wiki/Special:FilePath/Japanese atrocities. Philippines, China, Burma, Japan - NARA - 292600.jpg?width=200 "Prisoner of war exhibiting muscle loss as a result of [[malnutrition]].")
![[[Jogging]] is one form of aerobic exercise.](https://commons.wikimedia.org/wiki/Special:FilePath/Jogging couple.jpg?width=200 "[[Jogging]] is one form of aerobic exercise.")
![In [[muscular dystrophy]], the affected tissues become disorganized and the concentration of [[dystrophin]] (green) is greatly reduced.](https://commons.wikimedia.org/wiki/Special:FilePath/MuscularDystrophy.png?width=200 "In [[muscular dystrophy]], the affected tissues become disorganized and the concentration of [[dystrophin]] (green) is greatly reduced.")
![Structure of muscle fibre showing a sarcomere under [[electron microscope]] with schematic explanation.](https://commons.wikimedia.org/wiki/Special:FilePath/Sarcomere.gif?width=200 "Structure of muscle fibre showing a sarcomere under [[electron microscope]] with schematic explanation.")
Definición
Wikipedia
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle tissue, and are often known as muscle fibers. The muscle tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres.
Skeletal muscles are voluntary muscles under the control of the somatic nervous system. The other types of muscle are cardiac muscle which is also striated and smooth muscle which is non-striated; both of these types of muscle tissue are classified as involuntary, or, under the control of the autonomic nervous system.
A skeletal muscle contains multiple fascicles – bundles of muscle fibers. Each individual fiber, and each muscle is surrounded by a type of connective tissue layer of fascia. Muscle fibers are formed from the fusion of developmental myoblasts in a process known as myogenesis resulting in long multinucleated cells. In these cells the nuclei, termed myonuclei, are located along the inside of the cell membrane. Muscle fibers also have multiple mitochondria to meet energy needs.
Muscle fibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments called myofilaments, repeated in units called sarcomeres, which are the basic functional, contractile units of the muscle fiber necessary for muscle contraction. Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules that are used to power the movement of the myosin heads.
Skeletal muscle comprises about 35% of the body of humans by weight. The functions of skeletal muscle include producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. Skeletal muscle is also an endocrine organ. Under different physiological conditions, subsets of 654 different proteins as well as lipids, amino acids, metabolites and small RNAs are found in the secretome of skeletal muscles.
Skeletal muscles are substantially composed of multinucleated contractile muscle fibers (myocytes). However, considerable numbers of resident and infiltrating mononuclear cells are also present in skeletal muscles. In terms of volume, myocytes make up the great majority of skeletal muscle. Skeletal muscle myocytes are usually very large, being about 2–3 cm long and 100 μm in diameter. By comparison, the mononuclear cells in muscles are much smaller. Some of the mononuclear cells in muscles are endothelial cells (which are about 50–70 μm long, 10–30 μm wide and 0.1–10 μm thick), macrophages (21 μm in diameter) and neutrophils (12-15 µm in diameter). However, in terms of nuclei present in skeletal muscle, myocyte nuclei may be only half of the nuclei present, while nuclei from resident and infiltrating mononuclear cells make up the other half.
Considerable research on skeletal muscle is focused on the muscle fiber cells, the myocytes, as discussed in detail in the first sections, below. However, recently, interest has also focused on the different types of mononuclear cells of skeletal muscle, as well as on the endocrine functions of muscle, described subsequently, below.
