Synonyms
Overview Musculature, muscles, muscle mass, muscle circumference, torn muscle fiber, bodybuildingOur body has about 650 muscles, without whose existence humans would not be able to move. Each of our movements or postures requires an activity of certain muscles. Scientific studies have shown that the muscles of the eyes relax and contract about 100,000 times a day.
In addition, a person needs about forty muscles to frown, whereas only seventeen muscles are needed to laugh. Muscle movements can only take place in connection with the nervous system and the brain. Through our sensory organs we perceive stimuli and sensations, which are transmitted to the brain via the nervous system.
The brain reacts with corresponding “commands”, which are then passed on to the muscles by the nervous system. The internal organs also have a muscular system, the so-called organ musculature, which is constantly in action. They cannot be consciously controlled.
An example of this is the lung musculature. We cannot consciously release them from action. It must therefore be kept in mind that there are different types of musculature.
A distinction is made between: Our musculature, which as already mentioned above comprises approx. 656 muscles, weighs more than our skeleton. While muscles make up about 40% of our body weight, the skeleton accounts for only about 14%.
- The involuntary (= smooth) musculature
- The random (= cross-striped) musculature
- The heart muscle (special cross-striped muscles)
Muscular structure
When looking inside the muscle, it is noticeable that it is composed of several bundles of individual muscle fibers (= muscle cells). The muscle fiber: The picture shows the structure of a striated muscle. You can see that a muscle fiber contains myofibrils, which consist of actin and myosin filaments.
While the actin filaments are connected to each other at the so-called Z-lines, the myosin filaments are located unconnected between the actin filaments. Both components of the myofibrils bear the main load during any muscle contraction. The muscle fiber is protected by an elastic connective tissue.
In addition to its protective function, this connective tissue ensures that the different functional units of a muscle are connected. It is the elasticity of the connective tissue that ultimately makes muscle movement possible.
- Z-Strips
- Actin filament
- Myosin filament
If you compare the distance between the Z-stripes you can see the contraction.
In general, muscles convert chemical energy into work. This requires a chemical energy source. ATP (= Adenosine – tri – phosphate) serves as such.
The task of myosin is to convert the energy of the ATP cleavage into conformational energy in order to be able to move its own myosin head. The action of calcium (Ca2+) causes a conformational change in the area of the troponin – tropomyosin complex, whereby a connection (= bridging) is created between the myosin head and the actin filament. The supply of energy causes a structural change within the myosin molecule.
This causes the myosin head to tilt by about 45°. It thus slightly shifts the actin filament. Shortly after the tilting, the connection is broken again and a new cycle can be started immediately.
The cycle described above is an explanatory model (= sliding filament theory), which attempts to explain muscle contraction as the result of numerous biochemical and physiological investigations. The chain of different tasks runs in a matter of seconds. The individual myosin heads do not work synchronously, because while some of them tip over, others already straighten up again.
Since the actin filaments are always moved towards each other, the shortening during muscle contraction can be explained The smooth muscles differ from the striated muscles described above only in that they have tropomyosin but no troponin. As a result, the binding of myosin to actin, which in turn causes the movement of the myosin head, has to be carried out differently. In smooth muscle, the reaction chain is triggered by phosphorylation of the myosin chains.
- The Ca2+ – ions are released.
- ATP – energy is converted by myosin into its own conformational energy.
- Ca2+ – binding to troponin C causes conformational change of the troponin-trypomyosin complex.
- Myosin – Binding site on actin becomes accessible
- Bridging between actin and myosin filaments
- Tip over of the myosin head.
- Disconnecting the connection .
- Erecting the myosin head.
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