The whole process of muscle cells from excitement to muscle contraction

The action potential extends to the deep transverse tube of the cell, so that the sarcoplasmic reticulum releases calcium ions into the cytoplasm, the calcium ions bind to calmodulin, the conformational changes, the contact bridge is inhibited by actin, the thickness of the muscle filaments slides relatively, and the muscle contracts.

The rhythmic contraction of the heart muscle promotes blood circulation, the contraction of skeletal muscles produces various body movements, and the contraction of smooth muscles causes the movement of internal organs and blood vessels. Although the structure, distribution, and functional characteristics of these three are different, from the perspective of molecular biology, the contraction principle of the three types of muscle cells is similar.

Since 1953, when HT and Xley put forward the theory of muscle filament, great progress has been made in the observation of the ultrastructure of muscle cells, the biochemical study of myofibrillar contractile protein, and the excitator-contraction coupling of the muscle contraction system, and the research on the principle of muscle contraction has made a breakthrough. Obviously, the elucidation of these topics will contribute to the clinical diagnosis of myocardial and skeletal muscle diseases.

This article intends to focus on the principle of skeletal muscle contraction, and also involves some characteristics ,... of cardiac muscle and smooth muscle

Summary. Based on biomechanical principles, muscles are elongated before contracting, which improves muscle tone and thus better stretching ability.

Why does contraction before stretching muscles improve muscle strength? The mechanism is explained by the principles of exercise physiology.

Based on biomechanical principles, muscles are elongated before contracting, which improves muscle tone and thus better stretching ability.

The morphology of muscle contraction is divided into dynamic collapse and static. The movements of fitness training are completed by dynamic isotonic contraction. When the muscles are isotonic contraction, the strength of the muscle isotonic contraction also changes due to the change in the joint angle caused by lifting weight, which is closely related to the principle of the lever of the object and the effect of movement.

Let's take a look at each of them. Static: Also known as Lu Xiao's isometric contraction, it refers to the fact that the muscle is well formed during isotonic contraction, its length does not change, and the angle of the two ends of the muscle across the joint and attached to the bone does not change.

Dynamics can be divided into: isotonic contraction: refers to the contraction of muscles under a constant load or weight.

Isokinetic contraction: This is when the muscles contract and stretch at a fixed rate. Centripetal contraction and eccentric contraction:

When a muscle is contracting, its length shortens and is called a concentric contraction. Conversely, when the muscles are elongated as they are stretched, it is called eccentric contraction. Strong contraction:

Before the muscle is concentrically contracted, the centrifugal contraction action is to elongate the muscle to be carried out to increase its contraction amplitude, so that the centripetal contraction of the muscle can produce greater force.

Based on biomechanical principles, muscles are elongated before contracting, which improves muscle tone and thus better stretching ability.

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<> be in detail. Specific physiological principles explain this mechanism.

Rapid stretching and contraction of the muscles, i.e., rapid stretching and contraction, is defined as a rapid and powerful action followed by explosive centripetal contractions after eccentric contractions, which is accomplished by the elongation-shortening cycle or centripetal-centripetal coupling phase. However, continuous static stretching will inhibit this reflex, which is why it is recommended not to do static stretching before exercise, which will inhibit the activity of the muscle spindle and thus cause a decrease in explosive power. In fact, the Stretch-Contraction Cycle (SSC) is like a rubber band, and when the muscles are stretched from rest, they allow us to generate more force.

Before the muscle is concentrically contracted, the centrifugal contraction action is to elongate the muscle to be carried out to increase its contraction amplitude, so that the centripetal contraction of the muscle can produce greater force.

Before the muscles do centripetal contraction, they should do eccentric contraction, that is, the muscles to be moved are elongated to increase the contraction amplitude of the muscles.

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, and it has the properties of ATPase and has two binding sites, one with ATP and the other with myofiin on the fine muscle filament. In the fine muscle filaments, there are many sites on the myogenic protein that bind to the Hengxian bridge. During muscle relaxation, the position of tropomyocoin 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 the condensin of the muscle.

2.Myosaline gliding process: 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 promyosin to roll and dislocate, exposing the masked binding site.

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 resting configuration, and the tropomyogin returns to its original position and covers the binding site again.

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 them throughout the 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.

According to the now widely accepted sliding model, muscle contraction is produced by the sliding between myosin and actin. Actin filaments (filaments) gliding on top of myosball egg filaments (thick filaments). The length of the myosin filaments and actin filaments themselves remained unchanged throughout the contraction.

The protrusions of myosin filaments (called crossbridges or crossbridges) and some special locations on actin filaments form a complex protein called actomyosin, which can cause muscles to contract under the action of ATP.

When the muscle contracts, if the actin filament glides inward, so that the z-line is dragged towards the sarcomere** and the muscle is shortened, this is called centripetal contraction (also known as concentric contraction).For example, when you perform a pull-up movement, when the biceps muscles are tense (contracted) and shortened, lifting the body upwards, it is a centripetal contraction. Conversely, eccentric contractions are underway when the actin filaments glide outward during the descending phase of the pull-ups, causing the sarcomere to lengthen and return to its original length in a controlled manner.

In another case, the actin filament does not slide when the muscle contracts and remains in its original position (e.g., when doing a pull-up, only the body is hung on the bar), which is called an isometric contraction.

Since the muscles still have a considerable degree of elasticity when they are relaxed, it is believed that there are still a certain number of crossbridges working at this time. Even with the muscles relaxed, 30% of the crossbridge is still performing the task.

Summary. 1) Myogenic factors.

1. Muscle cross-sectional area: The physiological cross-section of the muscle is an important factor in determining the strength of the muscle, and the larger the physiological cross-section, the greater the force generated by muscle contraction.

2. Types of muscle fibers: fast muscle fibers can produce greater contraction force than slow muscle fibers.

3. The initial length of muscles: the strength of human muscles is related to the initial length of muscle contraction.

4. Joint movement angle.

Failure to improve the contractility of muscle cells is (

1) Myogenic factors 1, muscle cross-sectional area: the physiological cross-section of the muscle is an important factor in determining the strength of the muscle, the larger the physiological cross-section, the greater the force generated by muscle contraction. 2. Types of muscle fibers:

Fast-twitch twitch fibers produce greater contractility than slower spini-beam fibers. 3. The initial length of muscles: the strength of human muscles is related to the initial length of muscle contraction.

4. Joint movement angle slag filial piety.

2) Neurogenic factors 1, central activation 2, central nervous system coordination and control of muscle activity 3, central nervous system excitatory state.

3) Other factors 1, age 2, gender 3, hormone effect 4, strength training.

The reflex arc consists of five parts: receptors, afferent neurons (sensory neurons), nerve centers, efferent neurons (motor neurons), and effectors (muscles, glands).

Contraction of skeletal muscle:

First, the instructions issued by the central nervous system are transmitted along the motor nerves of the body in the form of nerve impulses (action potentials) and transmitted to muscle cells, a process called excitatory transmission between nerves and muscles.

Secondly, the action potential on the surface of the muscle cell membrane is transmitted to the inside of the muscle cell through the triple tube structure of the muscle cell, triggering the release of the information substance Ca2+ from the sarcoplasmic reticulum to the sarcoplasm, and transmitting the information to the sarcoplasmic regulatory protein, a process called excitation-contraction coupling.

Finally, the high concentration of Ca2+ in the sarcoplasm triggers the binding of contractile proteins through the sarcoplasmic regulatory proteins, and causes the muscles to contract.