Skeletal muscles
Muscle contraction
Muscle metabolism
Muscle functions
The mobility of the human skeletal system is the responsibility of 350 smaller and larger muscles, which together make up the muscles of the head, the neck, the torso, the arms, and the legs. The skeletal muscle system, which is composed of striated muscle tissue, has the largest mass out of all of the body’s organ systems. Muscles are made up of muscle bundles consisting of striated muscle fibres. Both the bundles and the muscles themselves are enclosed in a case of connective tissue. Muscle contraction is an energy-intensive process; the muscle fibres are provided nutrients and oxygen by a dense network of veins. The muscles are connected to the bones by tendons made up of fibrous connective tissue. The points of connection are the origin and the insertion. The shift happens in the location of the latter.
The striated muscles’ operating unit is the multinucleate muscle fibre, which is elongated in shape, with an ordered system of protein filaments inside. These are the muscle filaments, which are positioned like two hands pointing at each other with their fingers, or two combs facing each other by the teeth. The muscle fibres’ contraction is caused by the opposing muscle filaments’ ability to slide in between each other. Since one of their ends is anchored, the muscle fibre itself, too, shortens when the muscle filaments slide in between each other, and the shortening of the fibres in turn causes a change in the form of the whole muscle. When the muscle relaxes, the muscle filaments slide back apart into their original position.
The basis for muscle function is the muscle filaments’ intersectional sliding movement, which is an extremely energy-intensive process. Working muscle fibres use up 20-100 times as much energy as when they are in a relaxed state. In muscles with an adequate supply of oxygen, the energy needed for contraction is derived mostly from the biological oxidation of glucose. While using the energy produced from glucose, carbon dioxide and a considerable amount of heat are also released. Glucose is stored by muscles only in small amounts, therefore it is the veins densely covering the muscles that transport glucose and oxygen, which are the base materials for biological oxidation, to the muscle fibres. During itense and lasting muscle function, the muscle’s vein network does not provide enough oxygen, so fermentation takes place inside the muscle fibres. In this process, the breakdown of glucose is carried out in a different way; less energy is gained, but lactic acid is also produced. Muscle fatigue and muscle fever as a result of muscle work that exceeds fitness level is caused largely by the lactic acid that accumulates in the muscle fibres.
Muscles contract as a result of a stimulus. The contraction stimulus originates directly from a nerve cell. We operate some of our skeletal muscles voluntarily, others contract and relax involuntarily. If only one stimulus reaches the muscle, the result is a convulsion, which means that the muscle slightly contracts for a short period of time, and then relaxes. If multiple successive stimuli reach the muscle, then, depending on the density of the stimuli, complete muscle
contraction can take effect. Inside the skeletal muscle system there are muscle pairs whose functioning results in each muscle moving in an opposite direction to the other, such as the
flexor and extensor muscles. In the limbs, when the flexor muscles operate, the joints bend, and when the extensor muscles operate, the joints extend.
Besides the muscle pairs that move in opposite directions, there are also lots of muscles in the skeletal muscle system that work together and help each other during a specific movement. For example, inside the torso’s complex muscle system, the contractions and extensions are generally not the responsibility of a single muscle, but are
carried out with the cooperation of muscle groups.
