There are sternocleidomastoid muscles in the neck: located on both sides of the neck, the head bends to one side and the face rotates to the other side, and the outline of this muscle can be observed. There are trapezius muscle and erector spinae in the back: trapezius muscle is located in the back and nape, both sides contract at the same time to make the head lean back, and erector spinae is located in the middle of the back, which is used to make the spine stretch back and raise its head. Pectoralis major: located in the chest, it makes the shoulder joint adduction, pronation and flexion. There are rectus abdominis in the abdomen: located on both sides of the anterior midline of the abdomen. There are deltoid, biceps brachii and triceps brachii in upper limbs: they participate in the movements of shoulders and upper limbs. The lower limbs include gluteus maximus, quadriceps femoris and gastrocnemius: they participate in the movement of buttocks and calves.

structure

There are about 639 human muscles. It consists of about 6 billion muscle fibers, the longest is 60 cm, the shortest is only about 1 mm, the big muscle weighs about two kilograms, and the small muscle weighs only a few grams. The average person's muscles account for about 35% to 45% of the body weight.

According to the different structure and function, it can be divided into smooth muscle, myocardial muscle and skeletal muscle, and according to the shape, it can be divided into long muscle, short muscle, flat muscle and orbicularis oris muscle. Smooth muscle is mainly composed of internal organs and blood vessels, which has the characteristics of slow contraction, long duration and no fatigue. Myocardium constitutes the heart wall, and neither of them contracts with human will, so it is called involuntary muscle. Skeletal muscles are distributed in the head, neck, trunk and limbs, and are usually attached to bones. Skeletal muscle contracts rapidly, forcefully and easily, and can contract and contract with people's will, so it is called voluntary muscle. Skeletal muscle is striated under the microscope, so it is also called striated muscle.

Skeletal muscle is the dynamic part of the exercise system, which is divided into white muscle and red muscle fiber. White muscles contract or stretch rapidly through rapid chemical reactions, while red muscles exercise through continuous oxygen supply. Under the control of the nervous system, skeletal muscles contract and pull bones to produce movement. There are more than 600 human skeletal muscles, which are widely distributed, accounting for about 40% of body weight. Every skeletal muscle, regardless of its size, has a certain shape, structure, position and auxiliary devices, and is rich in blood vessels and lymphatic vessels, which are controlled by certain nerves. Therefore, every skeletal muscle can be regarded as an organ.

Head muscles can be divided into facial muscles (expression muscles) and masticatory muscles. Trunk muscles can be divided into dorsal muscle, pectoral muscle, abdominal muscle and diaphragm. Lower limb muscles are divided into gluteal (broad) muscles, thigh muscles, calf muscles and foot muscles according to their positions, which are stronger than upper limb muscles and are related to supporting weight, keeping upright and walking. Upper limb muscles are divided into shoulder muscles, arm muscles, forearm muscles, hand muscles and neck muscles.

classify

skeletal muscle

It is a type of muscle that can be seen and touched. When bodybuilders increase muscle strength through exercise, they exercise skeletal muscle. Skeletal muscles are attached to bones and appear in pairs: one muscle moves bones in one direction and the other moves bones in the opposite direction. These muscles usually contract at will, which means that when they want to contract muscles, the nervous system will instruct them to do so. Skeletal muscle can contract for a short time (twitching) or for a long time (tetanus).

Red and white muscle fibers

Skeletal muscle of human body can be divided into red muscle and white muscle. Red muscle fibers rely on hemoglobin for continuous oxygen supply and long-term contraction and stretching, so that we can carry out daily behavior activities. White muscle fibers expand and contract rapidly through internal rapid chemical reaction (mostly in emergency), which is characterized by long duration and short reaction time, and its reaction time is one quarter of that of red muscle fibers.

smooth muscle

It exists in digestive system, blood vessels, bladder, respiratory tract and female uterus. Smooth muscle can stretch and maintain tension for a long time. These muscles don't contract at will, which means that the nervous system will automatically control them without thinking. For example, the muscles of the stomach and intestines perform tasks every day, but people generally don't notice them.

myocardium

Only in the heart, its biggest feature is endurance and firmness. It can stretch as limited as smooth muscle or contract as powerfully as skeletal muscle. It's just a twitching muscle that doesn't automatically contract. The heart muscle has a fixed contraction law, thus producing a heartbeat. Normal pacemaker cells are normal, and the regularity of myocardial contraction is certain. If pacemaker cells are abnormal, the regularity of myocardial contraction will change.