Muscle is everywhere - even in the eye! They make up almost half of our weight. Without muscles, the body would not move, and you would look like a flat tire. In all vertebrates, and therefore in us, there are three types of muscle tissue.
Smooth muscles
Smooth tissue is present in various internal organs, incl. in the intestines, blood vessels, and ducts (e.g. bile in the liver). Smooth muscles (and heart muscles) are innervated by the so-called autonomic nervous system. Its action is independent of our will and therefore we cannot, for example, control the contraction and relaxation of blood vessels or slow down or accelerate the heart's activity (Figure 1). We owe the agile movements and control of the body to smooth muscles located in the organs. We cannot consciously control them because they function automatically. They narrow or widen the lumen of the ducts leading to the salivary glands, pancreas, bile ducts or blood vessels. Thanks to them, the intestine contracts in sections (narrows), then this contraction moves towards the anus, thus pushing the food content.
Cardiac muscle
The walls of the heart are made of the tissue of the heart. It works automatically, rhythmically and continuously throughout our lives, shrinking over 100,000 times a day. times and pumping during this time about 10,000. liters of blood. To imagine how hard the work is doing, it is enough to realize that these 10,000. liters is quite a large petrol tank (picture 2).
Skeletal muscles
Agile movements and body control are the role of skeletal muscles. When a muscle contracts, its length decreases and its cross-section increases. As it contracts, it attracts to what it is attached to. For example, a large muscle in the back of the thigh will contract and pull on the tibia, thereby bending the knee joint. But for the leg in the knee to straighten, it is not enough for the muscle to relax. At the same time, the muscle in the front of the thigh (the so-called quadriceps) must shorten, pulling the tibia forward. This is why many muscles in our body function in pairs
- one pulls in one direction and another in the opposite direction. There are also flat skeletal muscles that make up the abdominal wall, for example. On the other hand, the circular muscles, which are not connected with the bones, are arranged in circles around the openings in the skin integuments (e.g. mouth, eyelids). As they contract, they close their mouthsor eyes. The muscles of the sphincters, e.g. of the urethra or anus, work in a similar way.
The muscles are responsible for all movements, from the blink of an eyelid to the record long jump. This also applies to movement within the body. The heart beats, food is transported through the intestines, blood vessels contract in frost because the muscles are constantly working.
Tireless heart pumping blood
The muscle tissue that the heart is made of has the properties of both the striated muscle (visible myofibrils) and the smooth muscle (action independent of our will). The heart cells are connected with the neighboring cells by means of protrusions, i.e. cytoplasmic processes. There is another feature that is unusual for other tissues. There are fibers in the heart muscle that differ from the main muscle mass. They are brighter, which in some animals can even be seen with the naked eye. These are transformed muscle cells that form the so-called the heart's conductive system. At the border of the ventricles and atria, these specialized cells form two clusters - the sinoatrial node and the atrioventricular node. They generate electrical impulses that cause the heart to contract. Bundles extend from the nodes distributing stimuli to the entire heart muscle.
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