Slightly less than half the body weight of a person is muscle. Types of muscles are divided depending on the purpose, functions performed, subordination to the nervous system, fiber structure. Without them, it is impossible to move around, to maintain normal processes of life and the constancy of the internal environment.
Musculoskeletal system
The skeleton and muscles make up the human skeleton. Bones play the role of supporting structures. Skeletal muscles are attached to them with the help of connective tissues. They, unlike bones, are elastic and can be deformed.
Their main functions - contraction and relaxation - make it possible for a person to move around in space. The skeletal muscle responsible for this process works on the principle of leverage. The passive part of the muscle (tendon) is attached to the bone at the optimal point for it to perform work. Another part of it is connected with a paired section of the skeleton.
At the junction of the bones is a joint, that is, their connection is mobile. With muscle contraction, the force transmitted through the tendons will move the bones.
Muscular system
The human body is segmented. Muscles (the types of muscles shown in the photo above) are not located in the reservoir, they are divided into departments. Coordinated work needs control. When moving a limb, it’s not just a contraction of a particular muscle. At the same moment, her antagonist relaxes. With the reverse process, the functions change: the flexor relaxes, and the extensor returns a part of the body to its original position.
The coordination of skeletal muscle movement is controlled by the brain. This process is to some extent subject to human consciousness. And although commands for basic movements are not given in the literal sense, they are still present in intentions, and the brain instantly transforms them into signals that are understandable to the muscles.
There is another muscle system that the human will is completely not subject to (involuntary). This is mainly the muscles of the internal organs. The heart muscle is allocated generally in a separate group. A person does not control its reduction and, under normal conditions, does not notice. The functions of the muscles of the stomach, bladder, intestines, and vascular walls are different. But their main task is to maintain the tone of a specific body and ensure that they can perform the necessary functions.
Muscles: Types of Muscles
The classification is made according to several factors. The main division is related to general purpose. Musculature of the skeletal and internal organs is isolated. Arbitrary subordinate muscles have mainly transversely directed fibers, and involuntary (internal) muscles are smooth.
Depending on the localization, the muscles of the head, limbs, and trunk are divided. From what work they perform, among them are determined flexors and extensors. By type of activity, synergists, that is, performing similar functions, and antagonists acting as a counterweight are distinguished among the muscles. In shape, they can be: short and thick, long and thin. The latissimus muscles belong to the flat muscles of the back. They are responsible for pulling the shoulder to the body and pulling the arm back to the axis of the spine.
If a muscle brings a limb closer to the body during contraction, then it is defined as adducing. In the opposite case, they talk about the assignment role. If parts of the body are rotated (head, forearm, shoulder), they are classified as rotating.
There is a division depending on the number of large bundles of fibers: biceps (biceps), triceps (extensor of the arm), quadriceps of the thigh. Four components of this muscle are distinguished (types of muscles: straight, lateral, medial, intermediate). The largest is the diaphragm, the muscles of the buttocks, legs and back. The smallest is in the ear. The strongest are on the lower leg (calf) and chewing on the head.
Structure
The muscle tissue in the human body is composed of cells. They have an elongated shape and are capable of contracting due to the presence of special organelles (myofilaments) in them.
There are two types of fibers: white and red. This classification is relative. But the difference can be understood by the example of chicken meat (breast and drumstick). The first is white. The chicken’s chest does not work as often as the legs. She rarely flaps her wings, but they are capable of a sharp surge of activity, which makes it possible to rise into the air.
On the other hand, life spans on legs. Their tissues can work for a long time, but are not capable of such a sharp surge in activity. The chicken leg muscles are densely penetrated by a network of capillaries (hence the color), since they need more nutrition (constant and sufficient) to maintain tone.
According to a similar principle, the muscles of people are arranged. There is evidence that the average person has white and red tissue in a ratio of 4/6. Sprint athletes have a different picture. They have fast white muscles overweight. This is partly achieved by training, but not every person is capable of such a transformation.
Bundles of fibers
Skeletal muscles are characterized by a speed of contractions. The cells of their tissue are relatively large, elongated and multi-core (up to 100 or more). If you look at the slice under a microscope, it looks like it is streaked with alternating strips of light and dark color (striated). Smooth muscle tissue consists of mononuclear cells. They are more uniform and not so elongated.
The skeletal muscles are assembled from bundles of the first (thinnest), second (larger), etc. orders. From the method of placement, rectilinear muscles (rectus abdominis), oblique (abdomen: internal and external) and transverse (directed perpendicular to the vertical axis - transverse chest muscle) are divided with respect to the axis of the spine.
Depending on the location around the tendons, they are divided into parallel (spinous) and circular (mouth, sphincter of the rectum, vagina).
The tissue of the heart muscle is special. It consists of binuclear cells (cardiomyocytes). They are intertwined, so that they fuse with each other, connecting cytoplasm. A feature of the heart muscles is the ability to work rhythmically and continuously.
Work
Even with a seemingly calm state, the muscles are still ready for immediate contraction. This condition is called tone. Nerve impulses constantly come to all organs from the brain. In a relaxed state, the number decreases, but they are enough to exchange information. Without such control, it would not be possible to maintain the body in balance and a stable position.
The source of energy for working muscles is adenosine triphosphoric acid (ATP). It is formed as a result of a complex cycle of glycogen breakdown. Cell nutrition is carried out with a blood stream. From this it follows that all the main muscles must be densely braided by capillaries, arteries and veins.
They are not able to work constantly, rest is necessary. If this is neglected, then the working capacity is reduced, which is manifested by a violation of the conductivity of the pulses and the response to nervous excitement. Under intense loads, metabolic products accumulate, which prevents an even distribution of impulses.
Localization
The human body is built on the principle of bilateral symmetry, so all major muscles are paired or consist of two halves. Those located on the head participate in mimic contractions that make it possible to express emotions (joy, grief, fear, pleasure). Another important function is the operation of the oral apparatus (chewing, swallowing). They also provide eye function (eyeball movement, blinking of the eyelids).
On the neck, the muscles raise and lower the head, turn it and support it in the axis of the spinal column. On the torso, the front and back are distinguished. Divided into the upper section (the work of the shoulder girdle); chest (breathing); abdominal (abdominal tone). The largest portion of the back is covered by the broadest muscles. In addition to participating in the extension of the arm and circular movements of the shoulders, they form in the back, below the ribs, the body frame, covering the kidneys and liver. Active during swimming, work with a deep breath, raising the lower ribs.
In front, in the upper part, in the area of coverage, the pectoralis major muscles are leading. In the abdomen, it is a deep-lying and thin transverse muscle. It is it that resists gravity and maintains the constancy of the environment of the internal abdominal cavity. Together with the press provides a flat stomach.
At the junction of the trunk and lower extremities, the gluteus muscle (large, medium, small) occupies an important place. On the thigh, it is possible to distinguish semi-membranous, two-headed, short, long and large adductors. On the lower leg - calf, sole. And on the foot - flexors and extensors of the fingers.
Role for the body
Without proper activity, muscles in humans can atrophy. It is noticed that at minimal loads the cells are updated once every one to two weeks. When playing sports, this happens more often. The growth of muscle tissue under loads with extra weight occurs due to the fact that part of the muscle fibers breaks. The body seeks to recover, new cells grow, connections are updated. This is accompanied by an increase in their volume and mass.
In addition to the implementation of cardiac activity, maintaining the shape of the body, ensuring vertical position and movement of the muscles, a number of other equally important processes are possible: speech (larynx and tongue), breathing (diaphragm), digestion (esophagus, tone of the stomach, intestines). Excretion of metabolic products (bladder, sphincter of the rectum) is also provided.
If a person does not have the ability to control the activity of involuntary muscles, then voluntary (core muscles) can even be trained. Well, a healthy lifestyle and maintaining the body in good physical shape, as you know, is the key to good health and peace of mind.
Now you know what role muscles play in the body. Types of muscles differ in their structure and functions.