The movement of the joints of the limbs is due to the work of the muscles located on them. They consist of special fibers arranged in bundles. In the human body, there are about 400 muscles that, under the influence of impulses of the central nervous system, are able to change the position of the body.
Types of muscle tissue
Movement is impossible without muscle involvement. The total mass of such tissues in the body of an adult is in the region of 30-40%. In newborn babies, it is about 20%, in older people it decreases to 25-30%. But if a person remains active even at an honorable age, then muscle mass does not decrease, it remains at the same level.
Specialists distinguish different muscle groups depending on their location, functions, fiber direction. By location, these types of muscles are distinguished:
- superficial (located under the skin);
- deep;
- lateral;
- medial;
- outdoor;
- internal.
In shape, experts distinguish spindle-shaped, square, triangular, circular, ribbon-like muscles. By the number of heads, they can be two-headed, three-headed and four-headed. Depending on the direction of the beams, they are single-pinned, two-pinned, or multi-pinned.
Muscles are also distinguished by function. Some provide extension of the limbs, others - flexion. Separately, rotator-lifters, compressors (sphincter), diverting and adducing muscles are distinguished.
For example, the brachial biceps refers to spindle-shaped muscles . It is attached to the bone, which is a lever, and provides flexion of the arm at the elbow.
Biceps shoulder
The biceps of the
arm refers to the anterior muscle group. It is located on the front of the humerus. This long fusiform muscle has two heads. One of them is long, the second is short. They walk side by side, heading from top to bottom. At the level of the middle part of the shoulder, they are connected in the abdomen of a spindle-shaped form.
The long head of the biceps of the shoulder originates in the form of a rounded tendon in the superarticular tubercle of the scapula. It passes through the shoulder joint from top to bottom. Inside it, the tendon is covered with a synovial membrane. And in the area of the shoulder, it passes in the inter-tubercle groove. There, it is wrapped in a synovial intercuspid vagina.
The short head originates in the same place as the sphenoid shoulder muscle, at the apex of the sphenoid process. Together they connect in the middle of the humerus. This forms biceps, which is supplied with blood from the axillary, lower and upper elbow collateral, brachial and return radial arteries.
At the end there is a tendon of the biceps of the shoulder, which goes to the tuberous part of the radius. The transition from muscle to tendon tissue passes directly above or near the elbow joint. In the place of attachment of the tendon is a double-headed bag. From its front-medial side there is a wide, thin dense aponeurosis. It is known as the fascia of Pirogov. In front, he covers the ulnar fossa. This aponeurosis is woven into the fascia of the forearm.
Triceps muscle
A muscle is located along the posterior surface of the humerus, which provides extension of the arm at the elbow. It has a fusiform shape. The biceps and triceps brachii differ not only in location, but also in structure. Triceps has three heads: long, medial and lateral. The first of them begins on the subarticular tubercle of the scapula in the form of a rounded thick tendon. Often it connects to the tendon of the latissimus dorsi muscle. The muscle abdomen of this head passes between the round muscles (small and large) and stretches to the middle part of the humerus.
The lateral head is partially covered by the deltoid muscle of the triceps. It originates on the back of the humerus. The bundles from it go down medially so that they overlap the groove of the radial nerve.
The medial head is the shortest of the three presented. It begins with collected muscle bundles on the back of the humerus. A significant part of it is covered with a lateral head. Between them and the groove of the radial nerve is the brachio-muscular canal.
In the middle part of the back surface of the shoulder, all three heads are connected to each other and form the abdomen. It ends with a thick tendon, which is attached to a special process of the ulna.
Flexion and extension in the elbow joint of the forearm provide just the biceps and triceps muscle of the shoulder. Also involved in this process is the brachial muscle, called brachialis.
Leg muscles
From the back of the femur is the posterior muscle group. Two-headed, semi-tendon and semi-membranous muscles are referred to it. They all begin in the area of the sciatic tubercle. Their beginning is covered with the
gluteus maximus muscle.Moreover, if the semi-tendon and semi-membranous muscles are located medially, then the biceps occupy a lateral position. The femoral biceps are extended along the entire length of the femur; it has a fusiform shape. It is adjacent to the femoral broad lateral muscle. The femoral biceps muscle forms the lateral wall of the popliteal fossa. It can fulfill its functions due to its special structure and attachment to another bone.
It starts with two heads - long and short. At the beginning of the first of them is a short thick tendon. It is located on the surface of the sacro-tuberous ligament and sciatic tubercle. The muscle goes not strictly down, but obliquely in the lateral direction. The lower end is attached to the lower leg.
The short head of the biceps femoris begins from the posterior surface of the femur. Its lower edge ends at the tibia (tibia).
Both heads are connected in the area of the border between the lower and middle part of the femur. They pass into one common tendon. It passes from the back of the knee joint. The specified tendon is attached to the tibia (its head) and the outer part of the lateral condyle, related to the tibia. Partially, its fibers are woven into the fascia of the lower leg.
Bicep function
Depending on what kind of work the muscles can do, they are divided into flexors and extensors. These are oppositely acting muscle groups that provide limb movement. The bending muscle of the upper
arm is the biceps of the shoulder.
The functions it performs are as follows:
- bends the arm in the elbow joint;
- provides the ability to turn the brush out;
- strains the arm in the elbow joint.
The main flexor of the upper leg is the biceps femoris.
Functions of the leg biceps:
- extension and adduction of the thigh;
- straightening the body after tilting;
- flexion in the knee joint of the lower leg;
- turning to the outside of the leg, bent at the knee joint;
- maintaining equilibrium.
It is worth noting that problems with biceps, for example, its lack of strength or flexibility, lead to back pain, problems with knee joints, and poor posture.
Extension of the upper limbs is ensured through the activity of the triceps located along the humerus. The biceps and triceps may contract together or alternately. The movement of the leg in the knee joint is facilitated by the coordinated work of the biceps and quadriceps.
Leg extensor
The largest muscle in the human body is the quadriceps. It is located on the front surface of the thigh and provides the ability to extend the lower limb in the knee area. She is also responsible for hip flexion - bringing this part of the leg closer to the stomach.
The quadriceps consists of four beams. Each of them is considered a separate muscle, which has its own name. Separately, experts distinguish the rectus, broad lateric, medial and intermediate muscles.
All are attached to the patella. But each of them has its own functions. For example, the straight line is responsible for flexion of the hip and extension of the knee joints. But the intermediate, medial and lateral are necessary for extension of the lower leg.
Traffic provision
Without the coordinated action of the muscles, it would be impossible to flex or extend the limbs. Arbitrary movements of the biceps are regulated by the spinal cord. This becomes possible due to the alternation of the processes of inhibition and excitement, which take place in the spinal cord. The muscles responsible for flexion and extension of the limbs can be in a relaxed state at the same time. This occurs, for example, at a time when the arm is relaxed hanging along the body.
Their reduction occurs due to the activity of spinal cord neurons responsible for movement. The relaxation process is associated with inhibition of these cells of the nervous system. If a person holds a dumbbell in a straight outstretched arm, then the biceps and triceps will work simultaneously.
Upon receipt of nerve impulses, the muscle receives a certain command, depending on this, the process of relaxation or muscle tension begins. When contracting, it acts on the bone to which it is attached, as on a lever.
The principle of muscle functioning
Contraction of any muscle group is work that requires energy to complete. Its source may be products released during the decay and oxidation of various organic substances. In the fibers of muscles, they are subjected to various chemical reactions through the action of oxygen. The result of this interaction is the release of energy. This is accompanied by the formation of cleavage products - carbon dioxide and water.
With too much strain on the muscles, the natural process of fatigue begins. This is accompanied by a decrease in their performance. After rest, everything is restored.
It was noted that when performing rhythmic exercises, fatigue occurs a little later. Indeed, in the intervals between contractions, the muscles partially manage to rest and recover. But the intensity of the load also affects the performance. The higher it is, the faster fatigue will come.
CNS work
Making this or that movement, a person does not think. He does everything automatically. But at the same time, each motor act for the nervous system is a complex process, for the implementation of which it is necessary to use its various levels. All active movements are controlled by the brain. They are called arbitrary or conscious.
Before muscle contraction begins, the cerebral cortex receives special information about the state of the articular muscle fibers through special channels. She estimates how ready they are for the load. Therefore, it cannot be said that voluntary movements of the biceps are regulated exclusively by the spinal cord. After all, the bark controls the strength, sequence and duration of each of the contractions.
The motor centers are located in the frontal part of the brain of the cerebral cortex. It is in the front sections that all signals are integrated. After this, the formation of a model of future movement occurs.
In order for an arbitrary muscle contraction to occur, impulses formed in the cortical part of the brain must reach the corresponding muscles. They follow a special path, which experts call cortical-muscular. Arbitrary movements of the biceps are regulated by central and peripheral neurons. The first of them are the bodies of pyramidal cells with axons. The second is spinal cord cells.
Neurons connect the part of the cerebral cortex that is responsible for movement, special sections of the spinal cord and the brain stem. This whole complex is called the pyramidal system.
Possible problems
It happens when some part of the cortex-muscular pathway is affected. In this case, the muscles do not receive a signal from the cerebral cortex. Their arbitrary movements become impossible.
For example, with a partial lesion, the biceps cannot perform its functions in full. Depending on the location of the lesion, problems can occur in various parts of the body. Partial damage, as a rule, leads to paresis.
With such injuries, voluntary movements of the biceps are also regulated by the brain and spinal cord. But because of the violation of relations, violation, restriction of the intensity and strength of contractions is possible. Problems can be central or peripheral, depending on which neurons are affected.
Examination of such patients should be thorough. During its implementation, it is important to determine not only how the motor function was preserved, but also check for the presence of muscle atrophy. They also look at whether there are deformations of the chest or spine, whether there are minor muscle twitches.
But, it is worth noting that it is not always just because of problems with the cortex-muscular path that movements become impossible. For example, with pathologies of the articular apparatus, violations of proprioceptive sensitivity, the biceps of the shoulder may stop working. It will not perform its functions in full even if cicatricial changes in the muscles appear. Therefore, it is important to determine the reason why muscle contractions have become impossible. For these purposes, investigate how the patient can perform active and passive movements, evaluate his reflexes.