Hand - the upper limb of a person, musculoskeletal system , one of the most important parts of the body. With the help of hands, a person can perform many actions, the main of which is the ability to capture objects [4] .
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| Blood supply | , , , and |
| Innervation | , , , and |
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Content
Bone skeleton and areas of the arm
In the hand, the following anatomical areas and the corresponding bones (in italics) are distinguished:
- Shoulder girdle ( collarbone , shoulder blade )
- Shoulder ( humerus )
- Forearm ( ulna , radius )
- Brush
- Wrist (4 in the proximal row: scaphoid, lunate, trihedral, pea-shaped ; 4 in the distal row: trapezoid, trapezoid, capitate, hook-shaped )
- Metacarpus (5 bones)
- 5 Fingers (14 phalanges ): large, index, middle, nameless, little finger.
Also, each person has the so-called sesamoid bones , their position, size and quantity (sometimes reaching up to 2-3 dozen) are extremely variable.
In non-scientific literature and in society, the βshoulder girdleβ is called the word shoulder (the shoulder joint with the head of the humerus is also included in this term).
Muscle
The muscular system of the arm consists of several layers of muscles, and many muscles are thrown over more than one joint, so that when one muscle contracts, the position in several joints can change.
Innervation
The hand has an efferent and afferent innervation . Efferent fibers send signals from the spinal cord to the arm, and afferent fibers from the arm to the spinal cord (through the dorsal ganglia). The fibers are collected in nerves , and almost all of them are mixed, that is, they contain both efferent and afferent fibers.
Skin, muscle, and joint receptors
The hand is equipped with a huge number of sensory endings (when the hands are "numb", this is a sign that something is wrong with them).
How the brain controls the hand
The cerebral cortex contains areas responsible for the management of individual parts of the body. These areas are often depicted in the form of a homunculus - a small man spread out over the cortex. The manβs legs are located dorsally, that is, closer to the crown of the head, and the arms and face are ventral, that is, on the side of the head, with the hand following the torso and then the face. The homunculus has thumbs and a palm and relatively small forearm and shoulder. In fact, there is more than one homunculus in the cortex, but a lot, since in almost every specialized area both hands, head, and legs are represented. So, in the part of the cerebral cortex, which is called the primary motor cortex, there is a section that is activated every time a person makes a hand movement, and in the primary somatosensory cortex there is a section that is activated when a person touches an object with his hand.
In addition to the cortical departments, the centers responsible for controlling the arm are found in the cerebellum and its nuclei, thalamus , basal ganglia, brain stem and spinal cord. This complex network of interconnected neurons carries out a rich repertoire of hand movements, and there are automatic (for example, movements to maintain balance) and arbitrary (threading a needle, threading a blanket into a duvet cover) movements. The cerebral cortex is responsible for complex voluntary movements, and the centers of a lower level are responsible for automatic ones.
The movements of the fingers and the entire arm are possible through electrical stimulation of the brain. During surgery, this is done using electrodes applied to the surface of the brain, or inserted directly into the brain. When caressing, the mother also does this, performing smooth movements with her hand through the childβs hair, sitting next to him until he falls asleep. You can stimulate the brain through the skin and bone of the skull. For this, focal magnetic stimulation is used.
Injury
Due to the special active role of the hand in the life of a person, as well as distalness , the hand is the organ of the person most susceptible to injury .
Connection of bones of the upper limb [4]
| Joints | Articular surfaces | Type of joint | Axes of movement | Joint movement |
|---|---|---|---|---|
| Sternocleidomastoid art.sternoclavicularis | Sternum of the clavicle, clavicular notch | Saddle-shaped, complex | Multi-axis | Raising and lowering the clavicle, movement of the clavicle forward and backward, circular movement of the clavicle |
| Acromioclavicular art. acromioclavicularis | Joint surface of acromion, acromial articular surface of the clavicle | Flat | Multi-axis | Raising and lowering the clavicle |
| Brachial art.humeri | The head of the humerus, the articular cavity of the scapula | Globular | Multi-axis | Flexion-extension of the arm, abduction of the arm to a horizontal level. bringing the arm, turning the arms outward and inward, circular motion |
| Lokteva art. cubiti | - | Complicated | - | - |
| Shoulder art.humeroulnaris | The block of the humerus, the block-shaped notch of the ulna | Block-shaped, helical | Monoaxial (front axle) | Forearm flexion-extension |
| Plecheluchevoy art.humeroradialis | The condyle of the humerus, the articular fossa of the head of the ulna | Globular | Multi-axis | Turns of the radius around the longitudinal axis, flexion and extension of the forearm |
| Proximal radiolactic art. humeroradialis proximalis | Articular circumference of the radius, radial incision of the ulna | Cylindrical | Monoaxial (longitudinal spine) | Radial Turns |
| Distal radiolactic art. humeroradialis distalis | Joint circumference of the ulna, ulnar notch of the radius | cylindrical | Monoaxial (longitudinal spine) | Radial Turns |
| Wrist band art. radiocarpea | The carpal articular surface of the radius, the proximal surface of the scaphoid, lunate, trihedral bones | Ellipse. Complex | Biaxial (axis: sagittal, frontal) | Adduction-abstraction, flexion-extension of the brush |
| Mid-carp art. mediacarpea | Joint surfaces of the first and second row of wrist bones (except pea-shaped) | Blocky, complex | Monoaxial (front axle) | Flexion-extension of the brush |
| Metacarpal (2-5) artt.carpometacarpales | Joint surfaces of the second row of bones of the wrist and the base of 2-5 metacarpal bones | Flat | Multi-axis | Inactive |
| The carpal-metacarpal joint of the thumb of the hand art. carpometacarpalis pollicis | Joint surfaces of the trapezium bone and base of the 1st metacarpal bone | Saddle | Biaxial (axis: frontal, sagittal) | Flexion-extension of the thumb, abduction-bringing it, contrasting it with the rest of the fingers |
| Wrist artt.intercaepeae | Wrist bones facing each other | Flat | Multi-axis | Inactive |
| Metacarpophalangeal artt.metacrpophalangeae | Articular surfaces of the heads of the metacarpal bones and the base of the proximal phalanx | I finger is block-shaped, II-V fingers are spherical | Biaxial (axis: frontal, sagittal) | Flexion-extension, abduction-adduction of fingers |
| Interphalangeal artt.interphalangeae | Joint surfaces of the heads and bases of the articulating phalanges | Blocky | Uniaxial (front axle) | Phalanx flexion-extension |
Hand Technology
The most developed and effective organ tool was the primate arm , which is a complex kinematic chain made up of numerous articulated joints of its parts in the joints . Motility of the hand is unique. Its structure allows you to move objects in space in several ways. A straightened palm and finger, located horizontally, forms a platform. Items placed on top can be carried carefully, carefully and with minimal damage. This method of transfer does not bring unnecessary anxiety to both the transported item and the carrying tool (hand). A wasp located in the palm of your hand will not cause concern. At the same time, the wasp clamped by the hand will certainly sting this hand. The idea of ββcareful transfer of objects on a horizontal stand realizes itself well in the technique of transferring hot objects. To control the fire, it was necessary to move the hot coals without causing damage to the hands.
The thumb is located on the opposite side of the other four fingers. This design allows you to tightly capture large objects. The capture with any finger, together with the thumb, allows you to gently move small objects. The use of several fingers, taken together at the same time, allows holding objects so tightly and controllably that the held object can be moved along a predetermined path with an accuracy of a fraction of a millimeter. The hand can be folded into a cup. This allows you to move liquid water. Each of the five fingers moves independently of the rest. Thus, with the help of the hand, it is possible to produce pressure simultaneously at five points. The clever independent holding of two sticks with one hand allows the construction of forceps . At the same time, there are no claws on the fingers of the hand. Therefore, the way to capture small objects with a limb by pre-piercing primates is not available. And, finally, an object, squeezed in the brush, and then moved, with the release of the fingers can be thrown to a distance greater than the dimensions of a person.
See also
- Anatomical terminology
- Fist (hand)
- Muscles of the upper extremities
- Hand washing
Notes
- β 1 2 Foundational Model of Anatomy
- β 1 2 3 4 5 https://teachmeanatomy.info/upper-limb/vessels/arteries/
- β 1 2 3 4 5 https://geekymedics.com/nerve-supply-to-the-upper-limb/
- β 1 2 Shimkevich V.M. Ruka // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
Literature
- Shimkevich V.M. Ruka // Brockhaus and Efron Encyclopedic Dictionary : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.