Briefly describe the principles of skeletal muscle contraction and relaxation?

The first is neurotransmitters at the neuromuscular junction.

Transmission from the presynaptic membrane to the muscle membrane, giving rise to the postsynaptic membrane (i.e., the muscle cell membrane.

N-type cholinergic receptor NA ion channels are opened, and a large number of NA ions are influxed, resulting in local depolarization of the skeletal muscle cell membrane, and this depolarization to a certain extent can cause the action potential of the skeletal muscle cell membrane, that is, skeletal muscle excitation, through excitation-contraction coupling, the concentration of CA ions in the sarcoplasm increases, and troponin on skeletal muscle fibers.

binding, exposing the transverse bridge junction site with the coarse myomeral filament, the coarse myomeral transverse bridge binds to the fine myogenic filament, consumes ATP, the transverse bridge swings, and the muscle contracts; Then, the concentration of Ca ions in the sarcoplasm decreased, the transverse bridge dissociated from the thin muscle filaments, the Ca ions dissociated from troponin, and the muscles were relaxed.

The principle of skeletal muscle contraction and relaxation can be summarized as the theory of muscle filamentous gliding. When the concentration of Ca2+ in the sarcoplasm increases, troponin is combined with it and changes its conformation, which in turn causes the conformational change of tropomyosin, until its double helix structure undergoes some twisting and the transverse bridge binds to the binding point on the exposed myofidin, activates transverse bridge ATPase, decomposes ATP to obtain energy, and the transverse bridge twists in the direction of the M-line, dragging the thin muscle filaments to slide towards the dark band**. The thick and thin muscle filaments glide against each other, the muscle segments are shortened, the exposed bands are narrowed, and the muscles contract.

When the calcium pump of the sarcoplasmic reticulum **Ca2+, the concentration of Ca2+ in the sarcoplasm decreases, and Ca2+ separates from troponin, so that the tropomyolinin returns to the position between the transverse bridge and the myofin molecule, hindering the interaction between them, and muscle relaxation occurs.

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.

Muscle contractions can be divided into three forms.

1. Shorten the contraction (centripetal contraction).

Characteristics: The tension is greater than the applied resistance, and the muscle length is shortened.

Function: It is the main form of muscle movement, and it is the basis for achieving dynamic movement (such as arm swing, high leg raise, etc.).

For example, when the joint angle is 120°, the biceps contractile tension is the largest, and when the joint angle is 30°, the biceps contractile tension is the smallest.

2. Elongation shrinkage (centrifugal shrinkage).

Characteristics: The tension is less than the applied resistance, and the muscle length is elongated.

Function: cushioning, braking, deceleration, overcoming gravity.

3. Isometric shrinkage.

Characteristics: Tension is equal to applied resistance, and muscle length remains unchanged.

Function: Support, immobilize, and maintain a certain body posture. Its immobilization function can also create suitable conditions for the movement of other joints.

Such as: standing, hanging, supporting and other movements.

The basic functional unit of skeletal muscle contraction and relaxation is: the sarcomere.

Each muscle segment is composed of thick muscle filaments and play muscle filaments to contract skeletal muscles, that is, thin muscle filaments glide towards the middle of the thick muscles.

Skeletal muscle contraction and relaxation are generally done by means of exercise and rest

When exercising, skeletal muscles usually contract, causing the blood vessels around the bones to constrict, producing lactic acid and making the muscles more developed.

At rest, the skeletal muscles are at rest and the surrounding blood vessels are at rest, and the skeletal muscles may become dilated.

In the long run, skeletal muscles may be more relaxed, and it is easy to cause cramps and other symptoms due to sudden movements.

Skeletal muscle is a type of striated muscle, a muscle that attaches to bones.

The contraction of skeletal muscle in the human body belongs to: silver trillion segment.

a.Single shrinkage.

b.Tonic contractions.

c.Incomplete tonic contraction.

d.Completely strong and straight contraction.

Correct Answer: Guess Pei B