The human upper limb played an important role in the evolutionary formation of it as a biological species. In our article, we will consider parts of the hands of humans and animals, especially their structure and functioning.
General plan of the structure of the upper limb
The upper limb consists of two parts. The first is a belt consisting of a clavicle and scapula. The second component is attached to them - the skeleton of free limbs. It consists of one unpaired humerus. It is movably connected with the ulnar and radial, forming the forearm. The next parts of the hand are the hands. They consist of bones of the wrist, metacarpus and phalanges of the fingers.
Upper arm
The structure of this department includes paired clavicles and shoulder blades. These bones of the upper limb belt provide a movable connection of the skeleton of the trunk and the free part of the arm. The clavicle connects to the flat sternum on one side and the shoulder blade on the other. 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 significantly increases the amplitude of the movements of the upper limbs.
Lower arm
The bones of the skeleton of the free limb are connected movably and form several joints: sternoclavicular, humeral, ulnar, and wrist. All these structures have a single building plan. In any joint, the head of one bone enters the recess of the other. So that the contacting surfaces do not experience strong friction, they are covered with hyaline cartilage. Each similar structure is located in the joint bag, to which the 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 others. This is due to the ability of a person to conscious labor.
The structure of the hand in all animals such as chordates is similar. It consists of three departments: 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 bat group of mammals are adapted for active flight due to the presence of skin folds and elongated fingers. Ungulate animals got their name due to the presence of protective horn formations on their limbs.
The mechanism of the upper limb
All parts of the arms of humans and animals move due to the presence of muscles. They are attached to the bones using ligaments. The muscles that drive the limbs in motion are combined in two groups. The first bend the limb. For example, the biceps, or biceps, leads the arm to the body. The extensors perform the opposite action. In humans, this function is performed by triceps. The deltoid muscle acts in opposite directions. Its fibers, located on the front surface of the forearm, bend the arm. And those that are located on the reverse side - on the contrary.
There are various types of receptors in the skin of the hands. These are special sensitive formations that bind the body to the environment. They are able to convert various types of effects into nerve impulses. In this form, information enters the appropriate sections of the cerebral cortex. The pathways in this case are nerve fibers. In the brain, information is analyzed and in the opposite direction goes to the working body. 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 structural features perform many important functions. This is the ability to fly, get food, build shelters. The hand of man possesses the most perfect features, which determines his labor activity and is the basis of many evolutionary transformations.