The upper limb of a person played an important role in the evolutionary formation of it as a biological species. In our article, we will consider the parts of the human and animal hand, the features of their structure and functioning.
General plan of the structure of the upper limb
The upper limb consists of two parts. The first is the belt, consisting of the collarbone and scapula. The second component is attached to them - the skeleton of free limbs. It consists of one unpaired humerus. It is movably connected to the ulnar and radial, forming the forearm. The next parts of the hand are the hands. They consist of the bones of the wrist, metacarpus and phalanges of the fingers.
Upper arm
This department includes paired clavicles and shoulder blades. These bones of the girdle of the upper limb provide a movable connection between the skeleton of the torso and the free part of the arm. The clavicle on one side is connected to a flat sternum, and on the other - to the scapula. This bone has a slightly curved shape and is well palpable throughout. Its main functional feature in the body is the location of the shoulder joint at a certain distance from the chest. This greatly increases the rangeupper limb movements.
Lower arm
The bones of the skeleton of the free limb are connected movably and form several joints: sternoclavicular, humeral, ulna, radiocarpal. All these structures have a single building plan. In any joint, the head of one bone enters the recess of another. So that the contact surfaces do not experience strong friction, they are covered with hyaline cartilage. Each such structure is located in the joint capsule, to which ligaments and muscles are attached.
Some parts of the human hand have their own characteristics. For example, the thumb of the hand is opposed to all the rest. This is due to a person's ability to conscious labor activity.
The structure of the hand in all animals of the chordate type is similar. It consists of three sections: shoulder, forearm and hand. Their morphological features and differences are associated with the habitat of animals. So, in birds, in connection with their ability to fly, the upper limbs turned into wings. Moles and shrews get their food by making moves in the soil. Therefore, they have wide digging limbs. Representatives of the order of chiropteran mammals are adapted for active flight due to the presence of a skin fold and elongated fingers. Ungulates get their name from the protective horns on their limbs.
The mechanism of the upper limb
All parts of the hand of man and animals move due to the presence of muscles. They are attached to boneshelp of connections. The muscles that move the limbs are divided into two groups. The first bend the limb. For example, the biceps muscle, or biceps, leads the arm to the body. The extensors do the opposite. In humans, this function is performed by triceps. The deltoid muscle acts in opposite directions. Its fibers, located on the anterior surface of the forearm, bend the arm. And those that are located on the reverse side - on the contrary.
There are different types of receptors in the skin of the hands. These are special sensitive formations that connect the body with the environment. They are able to convert various types of influences into nerve impulses. In this form, information enters the corresponding parts of the cerebral cortex. The conductive pathways in this case are nerve fibers. In the brain, information is analyzed and in the opposite direction goes to the working organ. Several types of receptors are located in the skin of the hands. Mechanical perceive pressure and touch. The body perceives cold and heat with the help of thermoreceptors. But most of all, the skin of the hands and fingers is sensitive to the perception of pain. They are formed by nocireceptors.
The upper limbs, due to the peculiarities of the structure, perform many important functions. This is the ability to fly, get food, build shelters. The human hand has the most perfect features, which determines its labor activity and is the basis of many evolutionary transformations.
