The human arm is also called the upper limb. It serves as a gripping tool and helps with upright gait through balancing movements.
What is the arm?
The arm is subdivided into the upper arm, forearm and hand. It has the greatest range of motion of any part of the body. The arm and hand consist of a total of 30 bones. Evolutionarily, the arms are a further development of the forelimb in mammals. Accordingly, their most important function is food intake in the form of a grasping tool. Since humans have been able to walk on two legs, the arms have also served as an aid to balance when walking and running. This is particularly evident in the pendulum motion during jogging.
Anatomy and structure
The humerus forms the part of the arm closest to the body and houses the largest bone in the upper extremity: the humerus. This is connected to the scapula at the top of the shoulder joint and to the ulna and radius at the bottom via the elbow joint. Well-known and important muscles of the upper arm are the biceps brachii (“biceps muscle”) and the triceps brachii (“triceps muscle”). The biceps muscle functions as the forearm flexor, and the triceps as the forearm extensor. Thus, the triceps is the antagonist, i.e., opponent, of the biceps. The largest upper arm muscle is the deltoid muscle, which surrounds the shoulder joint from above. Its most important function is arm elevation. The forearm extends from the elbow joint to the carpus. It consists of two bones: ulna and radius. Both are tubular bones and are attached to the elbow and wrist joints. The ulna is much thinner and weaker than the radius. It is located on the little finger side, whereas the radius is found on the thumb side. A special feature in humans is that the ulna and radius are not fused together. This allows the wrist and forearm to rotate. The muscles of the forearm can be divided into four groups according to their function. The pronators (e.g. M.pronator terres, round inward rotator) enable the ulna and radius to rotate inward. The supinators include, for example, the M.supinator (outward rotator). It rotates the forearm outward. Furthermore, the forearm muscles include the hand and finger flexors, as well as the hand and finger extensors. The skeleton of the hand is composed of carpal bones, metacarpal bones and phalanges. The carpus consists of eight carpal bones (scaphoid, lunate, triangular, pea, large polygonal, small polygonal, capitate, hooked), which are connected to each other by ligaments and arranged in two rows of four nodes each. The tubular bones of the metacarpus are connected to these carpal bones. Humans have five metacarpal bones, which are arranged almost parallel. The metacarpal bones are divided into three sections: The base, which is in articulated connection with the carpal bones, the shaft, and the head. The five metacarpal bones are followed by the phalanges. In the case of the thumb, these consist of two phalanges, in all other fingers of three phalanges (base, middle and end phalanges). The individual phalanges are connected to each other by small joints. The muscles that move the hand and fingers are divided into flexor and extensor muscles. The musculature of the hand consists of a total of 33 muscles and has a very complex structure. A large part of the muscles originate in the upper or lower arm and continue only through tendons to the hands and fingers. On the hand itself run the so-called short hand muscles.They spread the fingers at the base joints or pull them together again.
Function and tasks
Due to the mobility in the arm, shoulder and wrist joints, the arm is the body part with the greatest freedom of movement. The wide range of motion offered humans the opportunity to use their front limbs as grasping tools. In addition, the pendulum movements of the arms are an important support when walking upright. They help balance and also cushion the up and down movements of the body, thus relieving the strain on the legs.
Diseases and ailments
Due to the extremely complex anatomical structure of the arms, the list of possible diseases is also varied. One of the most common diseases affecting the arms is tendonitis. They are usually caused by overuse and occur more frequently in the area of the hand or elbow joints. In osteoarthritis, too, the hands are among the most frequently affected parts of the body.Because bracing and catching with an outstretched arm is an instinctive action in falls, arm fractures are also often represented in emergency departments. Upper arm fractures, for example, account for about four to five percent of all fractures. Other complaints may include: Arm pain, Warm extremity, Cold extremity, Upper arm fracture, and Shoulder-arm syndrome.
