Theoretical Model: Organization of the Skeletal Muscle. Sarcomerus
Muscular tissue characteristics In order to comprehend the muscular tissue metabolism it is necessary to retain the following cells characteristics: High specialization level (contraction): Biochemistry structure, which allows this contraction, is the myofibrils. They do not reach mitoses nor do they regenerate themselves. Cell division is genetically inactivated. They grow when the cells volume rises. This is called hypertrophy. It happens due to a rise in the proteins’ synthesis speed (actinia and myosin). In this case, proteins degradation speed maintains itself constant. Muscular fibers have a high mitochondria density (thus favoring the oxidative phosphorilation) and a protein denominated mioglobine, which allows the oxygen fixation. These two characteristics allow a high and efficient TPA synthesis. We should not forget that muscular contraction implies a TPA high level of utilization. In the myocites’ cytoplasm we find a known formation of T tubules. These tubules are an encapsulation of the cell membrane: Nervous terminals reach this encapsulation (axons of the a moto-neuron), which will transmit the necessary electrical impulse for contraction. The structure formed by the nervous terminal and the T tubule is called Motor Plaque. The sarcoplasmic reticule (or endoplasmic reticule) is very developed within the myocites. This microscopic organism becomes the intracellular deposit of Calcium. This ion is indispensable for the propagation of the contraction signal. The fibers (myocites) group themselves forming fascicles. And fascicles do the same in order to form muscles. We can find two varieties of skeletal muscular fibers. In order to make this distinction the use of an electronic microscope is necessary.
Type I: they are small cells. In their cytoplasm we might find numerous mitochondria and abundant mioglobine. These myocites are much irrigated and receive a great amount of oxygen. Due to this factor, and compared to the Type II cells, their TPA hydrolysis speed is relatively low. And their contraction is slow. However, since they possess a high amount of TPA reserves, contraction ends to be persistent (higher resistance to tiredness). Mioglobine high presence gives it a reddish coloration. High percentages of this type of muscular fiber are to be found in posture and anti-gravitating muscles.
Type II: They are larger. Their mitochondria amount is lower and irrigation is less profuse. However, they possess a large sarcoplasmic reticule. These characteristics favor a fast liberation of calcium. This fact allows a very oldstrong contraction. Generally speaking the contractions are short and intense. There exists a great amount of glucolitic enzymes to allow a fast liberation of energy. Mioglobine’s deficit provokes a whitish coloration. Miofibriles We will now analyze the elements, which give a structure to the muscular fibers. Myofibrils are cylindrical structures formed by two contractile proteins: actinia and myosin. These proteins are polymerized and form microfilaments and their particular organization will origin the myofibrils. Secondarily, we also find other two proteins forming these microfilaments: tropomiosine and troponines (C, I and T). Actinia It is the main component of the thin microfilaments. We find it in two shapes: globular and fibrillar. Globular actinia (G) is formed by protein individual units. On the other hand, fibrillar actinia (F) is a polymerization of the actinia G units, which specially organize forming a sort of double helix. This structure maintains a stable constitution because of the presence of two other proteins: Troponine (three types): Troponine I that inhibits the union between actinia and myosin (necessary for contraction). At rest, it is united to actinia. During contraction, it frees it. Troponine C is a calcium linking protein. Once it links calcium, it separates Troponine I from Actinia, thus liberating the last one. Troponine T: its function is structural. It joins C and I Troponines with Tropomiosine. Tropomiosine: This protein covers the joining links between the myosin and actinia transversal bridges. During contraction frees these links allowing the union of actinia and myosin. Myosin Myosin forms thick microfilaments (myosin microfilaments). Myosin molecule is formed by a head (normally covered by a TPA molecule which has the ability to hydrolyze it) and a tail with a structural function. Sarcomerus It is the structural unit of the muscular contraction. It is formed by a regular sequence of dark and clear stripes, which give the myocite a typical striated aspect. We will now describe each of the stripes, which form a sarcomerus. Z Disks: they constitute the sarcomerus’ limits. A protein called actinine where the actinia microfilaments organize themselves forms them. I Band: this band is formed by actinia thin filaments, with no superposition whatsoever with other filaments. It is a clear band or stripe (in a polarized light microscope we can watch it as isotropic). It is located at the sarcomerus’ ends. During contraction it shortens. Its length diminishes since actinia will to a great extent superpose with myosin. A Band: myosin thick filaments form it. And two sections can be clearly be distinguished. One of them shows no superposition. The other one shows superposition of actinia and myosin filaments. It is a dark band (an isotropic) and it occupies the sarcomerus’ center. During contraction its length remains constant. H Band: It is formed by myosin filaments without any superposition (it is included within Band A). It shortens during contraction. M Band: It is found in the H Band middle. It is formed by proteins, which support and organize the thick myosin filaments.
Theoretical Model: Organization 
Type I: they are small cells. In their cytoplasm we might find numerous mitochondria and abundant mioglobine. These myocites are much irrigated and receive a great amount of oxygen. Due to this factor, and compared to the Type II cells, their TPA hydrolysis speed is relatively low. And their contraction is slow. However, since they possess a high amount of TPA reserves, contraction ends to be persistent (higher resistance to tiredness). Mioglobine high presence gives it a reddish coloration. High percentages of this type of muscular fiber are to be found in posture and anti-gravitating muscles. 
