make muscles

How do muscles work? How are they built? What is the difference between voluntary and involuntary muscles, and why are voluntary muscles striated and involuntary muscles smooth? Which muscles are the most important?

Author: Zvi Atzmon, young Galileo

Muscles are body tissues that can shorten, i.e. reduce their length, thus exerting force and causing movement. The action of the muscles allows movement of the entire body, movements of organs and movements within the body: the movement of blood in the blood vessels (blood circulation), the movement of food along the digestive tract, pushing the newborn from the womb into the world, and more.
The shortening of the muscles is also called contraction, but it is not the "muscle contraction" following particularly vigorous muscle activity. The action of contraction is made possible thanks to contractile proteins found in the muscle cells. These contractile proteins are of two types, which are combined with each other and can slide, like the fingers of the right hand can slide between the fingers of the left hand as the distance shortens. The two types of proteins are actin (from the word "action" - the action of the muscle) and myosin ("myo" - muscle in Latin).
The action of sliding and the progress of the myosin along the actin, which leads to the shortening of the muscle, requires energy, hence the need for food for muscle action. This action also creates heat, so you get warm when running, for example; and shivering (involuntary muscle action) when very cold. When a muscle works it shortens (contracts) or tries to shorten while exerting force. When the muscle is not working - it is limp. A muscle cannot lengthen by itself. It only lengthens when something (eg another muscle) stretches and lengthens it.
In our body there are three main types of muscles: voluntary striated muscles, involuntary smooth muscles, and the cardiac muscle, which is striated and involuntary.

Horizontal stripes

Striated muscles (also known as striated) are muscles in whose cells the myosin molecules are arranged parallel to each other, as is the actin, and therefore across the cell they look like stripes, or a horizontal drawing, hence their name. These muscles are attached to the bones of the body and cartilage, and therefore they are also called skeletal muscles. They are also called voluntary muscles because their action can be controlled by the cerebrum - whose activity induces in us the feeling of conscious will.
Not every action of a voluntary muscle is indeed voluntary. Voluntary muscles participate, for example, in performing reflexes, which are involuntary actions. In many cases voluntary muscles participate in automatic actions, which we do not think about. But if there are situations where we control the action of the muscle with our will - this is a voluntary muscle. For example, the breathing muscles are voluntary muscles, although they usually work when we are not thinking about them - even during deep sleep, and even if we lose consciousness when we faint or during an epileptic attack. But if a doctor or a swimming instructor tells us to stop breathing for a second (for example while diving) or rather to take a deep breath, then the voluntary nature of the respiratory muscles is revealed. The voluntary muscles, the skeletal muscles, are built from giant muscle cells (compared to other body cells), each of which contains many cell nuclei, whereas a normal cell in the body has a single nucleus.
There is no pass
In smooth muscles there is no lateral slip because the proteins that contract in them are not parallel to each other. Since they do not have stripes, they are called smooth muscles. Their cells are smaller and uninucleate. Smooth muscles are not attached to the skeleton - smooth muscles are found around the digestive tract, around the blood vessels (arteries and veins), around the bladder, around the pupil, and in other places in the body where there are no bones or cartilage. Their operation is not controlled by the big brain, which is responsible for the conscious will, and sometimes they operate without commands from the nervous system at all, not even from the involuntary nervous system.
Sometimes the smooth muscles work on their own. For example, because of different hormones. If the doctor or the sports teacher tells us to contract or relax the involuntary muscles in the walls of the blood vessels, we will understand that he was wrong or joking - we cannot control these muscles with our conscious will. At most we can put ourselves in a state of relaxation, and then the muscles in the walls of the arteries will perhaps be less contracted.
The smooth, involuntary muscles are divided into two groups: single-unit muscles and multi-unit muscles. In single-unit muscles, all the muscle cells are connected to each other electrically and functionally, and therefore if one works, all of them work. For example, the muscles in the wall of the bladder and the uterine muscle are like that. During the birth process, for example, the uterine muscle has to contract as a whole, as one unit, so that the newborn can be pushed strongly and come out into the world. In multiunit muscles, each muscle cell receives a direct nerve command from the involuntary nervous system and can contract independently of its neighbors. Multi-unit smooth muscles are, for example, the muscles that surround the pupil of the eye, which can expand or contract it to the exact extent necessary, and not necessarily to the maximum extent, like the uterine muscle.

The muscle our lives depend on

The heart muscle is a striated (striated) muscle, which is not a skeletal muscle and is not voluntary. The cells of the heart muscle are connected to each other in an electrical and functional connection - when the ventricles of the heart contract, the cells must all work together, otherwise, the blood will not be pushed and will not leave the heart for circulation.

The article was published in the Galileo Young Monthly for curious children. For a gift digital sheet Click