Briefly describe how muscle contraction and relaxation work

The occurrence of muscle contraction and stretching is determined by the shape and structure of muscle cells, which belong to a layered, strip-shaped, and dense structure, so muscle cells can glide smoothly with the contraction and stretching of muscles, resulting in aggregation and stretching in spatial distribution, which is the principle.

Myocytes produce action potentials, causing the concentration of Ca2+ in the sarcoplasm to increase, Ca2+ binds to troponin C, and troponin undergoes conformational changes, weakening the binding of troponin and actin, and conformational changes in tropomyosin.

The binding site on actin is exposed, the transverse bridge binds to actin, and the transverse bridge twists, dragging the thin muscle filament in the direction of the thick muscle filament**.

After the transverse bridge cycle composed of binding, twisting, dissociation, recombination and retwisting of the transverse bridge and actin, the thin muscle filaments continue to glide and the sarcomere is shortened. The energy ** of muscle contraction is the energy released by ATP water.

The principle of muscle contraction. The coarse muscle filaments have motor proteins that can be deformed by the energy of hydrolyzed ATP, and the thin muscle filaments have motor protein binding sites. Calcium ions expose the motor protein binding site on the fine muscle filament from the hidden position, so that the motor protein on the thick muscle filament can bind to and pull the fine muscle filament, resulting in the thin muscle filament and the thick muscle filament sliding against each other.

The thin muscle filaments and thick muscle filaments are still sliding, but the thick muscle filaments have just grabbed the thin muscle filaments, and the thin muscle filaments run back, and so on and so on, although they don't seem to move, they still consume energy.

Regarding muscle contraction, vertebrate bones contract by propagative activity, a single activity potential produces contraction repetitive activity, and the potential produces tonic contraction, and it is normal for muscles that do not contract through activity. The movement of muscles is different from person to person.

Sometimes the principle of muscle movement is a manifestation of physical health, and when there is an abnormal phenomenon in physical health, we need to consider whether the muscles are affected, and there are many diseases about muscle types. Therefore, the principle of muscle movement is very important, and parents must pay attention to it, and never cause damage to the body muscles because of some undesirable factors.

Fast-twitch fibers are a type of muscle fibers whose structural characteristics allow them to achieve the function of rapid muscle contraction. Fast-twitch fibers mainly have the following characteristics:

2.Low number of muscle fibers: Fast twitch fibers are less abundant than slow twitch fibers, but the baffle is that they can contract very quickly and produce high intensity of force, making them suitable for sports that require fast muscle blast.

3.Myofibrils in muscle fibers are densely arranged: Myofibrils in fast-twitch fibers are densely arranged, which helps to strengthen the contraction force of the muscles.

4.High myofibrillase content in muscle fibers: The myofibrillase content in fast-twitch twitch fibers is higher than that in the row, which helps to increase the rate of muscle contraction.

In short, the structural characteristics of fast-twitch fibers allow them to achieve the functions of fast muscle contraction and strong muscle explosiveness. Fast-twitch fibers play an important role in sports that require rapid muscle reflexes and high-intensity muscle activity.

Answer]: C Test Guidance] The small muscle is the area between the two z-lines on the myostophorifibrils, which is the most basic unit of muscle contraction and relaxation.

1. Describe the basic principles of muscle contraction.

Test Center] The conduction mechanism of excitation on the same muscle cell.

Analysis] Although there are differences in structure and function of different muscle tissues, the contraction mechanism is basically the same. Skeletal muscle is used as an example to illustrate the contractile function of muscle cells.

The shortening of the length of the muscles or the increase in active tension is called muscle contraction. The activity of the muscles is done in the form of contractions. In order to adapt to functional needs, myocytes have their corresponding structural differentiation.

Muscle cells are elongated in shape and have many myofibrils lined longitudinally on the inside. Myofibrils are made up of many sarcomeres in series. The sarcomere is the basic unit of muscle contraction.

The contraction process of muscle cells is as follows:

1.Composition of sarcomereThe sarcomere is made up of thick and thin muscle filaments. Thick muscle filaments are mainly composed of myosin.

The myosin molecule can be divided into a bulb head and a rod. The rod-like part aggregates into the main trunk of the thick muscle filament, and the head of the ball extends out of the surface of the thick muscle filament, forming a transverse bridge. Thin muscle filaments are composed of myosin, promyosin, and troponin.

The transverse bridge plays a key role in muscle contraction, it has the properties of ATPase, and has two binding sites, one with ATP and the other with myofin on the fine muscle filament. There are many sites on the fibrin in the silky remainder of fine muscle that bind to the transverse bridge. During muscle relaxation, the position of tropomyocolin is exactly between the myovin and the transverse bridge, which masks the binding point between the myofiin and the transverse bridge and prevents the binding of the transverse bridge to myosin.

2.When the intracytoplasmic Ca2+ increases due to the excitation of myocytes, Ca2+ binds to troponin on the filament, causing its configuration to change, thereby pulling the tropomyolinin to roll and shift, exposing the binding site that it masks. The transverse bridge immediately combines with myfibroin to form myfibrin, and at the same time, the ATPase on the transverse bridge gains activity, accelerates the decomposition of ATP and releases energy, causing the transverse bridge to twist, stretching the thin muscle filament and sliding into the thick muscle filament, shortening the sarcomere, and muscle contraction.

When the concentration of Ca2+ in the cytoplasm decreases, troponin detaches from Ca2+ and returns to the resting configuration, and the tropomyogin returns to its original position and covers the binding site again, and the transverse bridge cannot touch the fine muscle filaments, so that the muscle enters the diastolic process.

Within the whole, the function of skeletal muscles is directly controlled by the nervous system. When nerve impulses are transmitted to muscle cells, muscle cells generate action potentials and rapidly spread their trouser bases to the entire cell membrane, so that the entire muscle cells enter a state of excitatory contraction. The excitation of muscle cells is not the same as the contraction of cells, and there is a process in between.

This mediating process, which links the electrical excitation of myocytes with the mechanical contraction of myocytes, is called excitatory contraction coupling. The specific coupling process is as follows: First, the action potential of the cell membrane can be directly transmitted through the cell membrane of the transverse tube system that continues with it.

The action potential of the transverse tube can transmit the excitatory information to the final cistern of the longitudinal tube at the triple tube structure, so that the permeability of the longitudinal tube membrane to calcium ions is increased, and the Ca2+ stored in the cell will diffuse into the cytoplasm along its gradient, so that the concentration of cytoplasmic Ca2+ increases, and Ca2+ binds to troponin, resulting in muscle contraction.