Why do muscles contract and how do muscles contract?

Where does the power of man come from? It is produced by muscle contraction. If you bend your arm hard, you can feel a "pimple" on your arm.

This is caused by the contraction of the brachialis and biceps muscles of the upper arm, which allows the arm to bend and make a lifting motion. For example, when you clench your fist hard, your forearm becomes thicker because several muscles contract at the same time, so your fist is clenched tightly. Hundreds of muscles of different sizes and shapes are contracted under the innervation of the whole body to make a variety of different movements.

So, why do muscles contract? During muscle contraction, a series of biochemical changes occur. To put it simply, the changes go something like this:

Muscle contains about 20 percent protein (the remaining 75 is water and 5 is something else). Among proteins, there are myosinin and myofibrilin. These two proteins are filamentous and bind and shorten when the motor nerve center is excited, causing the muscles to contract.

Muscles contract to do work, and then energy is needed. The energy supplies contained in muscles include adenosine triphosphate, phosphocreatine and sarcosidin, which can release a large amount of energy when decomposed to meet the needs of muscle contraction. With regular exercise, muscle fibers become stronger and stronger, and the flexibility of the nervous system can also be improved.

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Problem description: Any motion of an object is formed by some of the most basic forces (such as magnetism, gravitational force) and so on. For example, apples fall because they are attracted to the earth. The motor can operate due to the repulsion or attraction of the magnetic field inside.

So what is the essence of muscle contraction? Don't tell me it's because I'm under **I want to know what the most basic force at work is.

Also, it seems that all the forces in nature can only be classified into a few types, but I wonder what they are?

Analysis: Huxley (1969) advocated a set of sliding filament theory as an explanation of the principle of muscle contraction. According to this theory, muscle contraction is caused by actin filaments (filaments) gliding on top of myosin filaments (thick filaments).

The length of the myosin filaments and actin filaments themselves remained unchanged throughout the contraction.

The actual situation of microfilament gliding still needs to be further explained, but it is believed that the protrusions of myosin filaments (called cross bridges) and some special positions on actin filaments form a complex protein called actomyosin, which can promote muscle contraction under the action of ATP.

When the muscle contracts, if the actin filaments glide inward, causing the Z-line to be dragged towards the sarcomere** and the muscle is shortened, this is called concentric contraction. For example, when performing a chin-up movement, when the biceps create tension (contraction) and shorten to lift the body upward, it is entering a centripetal contraction. Conversely, during the descent phase of the pull-ups, the actin filaments glide outward, causing the sarcomere to lengthen and return to its original length in a controlled manner, which is an eccentric contraction.

In another case, the actin filaments do not slide when the muscle contracts and remain in place (e.g., when doing pull-ups, only the body is hung on the bar), which is called isometric contraction.

Since the muscles still have a considerable degree of elasticity (muscle tone) when they are relaxed, it is believed that there is still a certain number of horizontal bridges working at this time. According to Yu and Brenner (1989), 30% of the crossbridge can still be performing the task, even when the muscles are relaxed.

After the action potential reaches the nerve endings during the transmission of excitation at the nerve-muscle junction, the voltage-gated Ca+ channel is opened, and the Ca+ inflow into the anterior membrane of the connector causes the release of ACH vesicles in the form of excellular, and the ACH binds to the posterior membrane of the connector, causing the chemical gating channel to open, and the strong Na+ inflow river and the weak K+ outflow produce an endplate reaction, and the EPP expands through tension, and finally depolarizes the muscle membrane to the threshold potential, resulting in the opening of the voltage-gated Na+ channel of the muscle membrane. The muscle membrane generates an action potential that completes the transmission of excitation at the nerve-muscle junction.

Features of neuro-muscle junction transmission:

First, it can only be transmitted in one direction, and the excitation can only be transmitted from the nerve endings to the muscle fibers, and cannot be carried out in the opposite direction;

2. There is a time delay: it is approximately necessary to reach the action potential from the nerve endings to the muscle membrane to generate the action potential;

3. Susceptible to environmental factors and drugs;

Fourth, maintain a "one-to-one" relationship, that is, every time the motor nerve impulse reaches the end, it excites the muscle cells once and induces a contraction. At the same time, cholinesterase can clear ACH in time to maintain this relationship.

Active muscle contraction can be good or bad, depending on the situation.

Generally speaking, active contractions occur when we exercise our muscles normally. Through active contraction, muscles are able to generate strength and movement. Proper active muscle contraction can enhance muscle strength and balance, help prevent injuries, and better complete complex fiber-carrying motor tasks.

However, if the muscles contract too strongly or too much, it can also lead to problems such as muscle fatigue and muscle strain. In addition, certain diseases and neurological problems can also cause abnormal muscle contractions, in which case it is necessary to seek medical attention**.

Therefore, there are both advantages and disadvantages to the slow imitation contraction of the muscle. When exercising, it is necessary to control muscle contractions moderately, pay attention to safety, and avoid overuse of muscles that can lead to muscle injuries.

Active muscle contraction is a type of muscle activity that contributes to muscle development, maintains muscle health, and helps to improve the precision of certain body movements. It can be achieved by spontaneous, passive, or slow-accommodating forced contractions of the muscles, and the degree of it can be changed later depending on the degree of tension in the muscles. It plays an important role in improving muscle strength, strength, endurance, and agility, so active muscle contraction is a great fitness activity that is beneficial for improving the overall function of the body.

Not good Chicken active contraction is very bad.