The human arm, also known as the free upper extremity, is the transformation or further development of the front limb into a gripping tool. However, it not only serves as a gripping tool, but also for balancing when walking upright.
Function of the arm
The upper extremity of the human body has the greatest possible freedom of movement of all parts of the body. This is achieved by the mobility in the
- Elbow and
- Wrist made possible.
The arm is divided into two parts, the individual parts of the arm being connected by joints. These serve not only to connect the individual parts of the arm but also to execute numerous movements. The upper arm consists of a large tubular bone (humerus).
This is connected to the shoulder and thus to the trunk of the body via the shoulder joint. This is a ball-and-socket joint, which allows three different directions of movement. The upper arm can be moved around a sagittal axis.
This is done by pulling the arm from the side towards the body (adduction), as well as the lateral movement of the arm away from the body (abduction). The limit of abduction is 90°, movement over 90° is called elevation. Various muscle groups are responsible for these movements, which are called the elevation movement.
Furthermore, a movement of the arm around a frontal axis is possible. This refers to the lifting of the arm forward (anteversion), or the return of the arm (retroversion). The last possibility is a rotational movement of the arm in the shoulder joint.
This rotation can be performed inwards (internal rotation) or outwards (external rotation). The rotation in the shoulder joint serves to support the rotation in the forearm: The elbow joint serves to connect the humerus with the two bones of the forearm (ulna and radius). Due to the different extensor and flexor muscles, extension and flexion can take place in the elbow joint.
But also the above mentioned pronation and supination is only possible due to the rotation of the spoke head in the elbow joint. In the wrist, the carpal bones close to the body (proximal) articulate with the bones of the forearm and the rows of carpal bones articulate with each other. The fingers themselves consist of numerous small bones, which are individually connected to each other by numerous joints, so that the fingers can still perform an opposition movement.
In this case the thumb is moved to the palm of the hand. Besides the bony connections between the different parts of the arm, the muscles also serve to connect the individual structures. In addition to the connection, they also mediate the individual movements of the three main joints and serve to transmit force.
For this reason, the individual muscles always pull over one of the different joints to bring it into motion. The individual vessels and nerves also originate at the shoulder or trunk and then continue to the individual fingers. This is how arterial blood and nerve innervation are supplied.
The veins and lymph vessels, on the other hand, collect the blood in the periphery, i.e. the fingers, and then supply it to the trunk. Thus, the veins and lymph vessels of the arm are also connected to each other, or merge into each other, and thus transport the various fluids. – Upper arm,
- Forearm and the
- Abductors, or
- Or elevators. – Rotation of the palm upwards = supination,
- Turning the palm downwards = pronation. – Bending (flexion, plamarflexion) and
- Stretch (extension, dorsal extension),
- As well as a spreading movement of the wrist.
- Can be stretched. – Furthermore, all fingers can be led away (abduction) and
- Are introduced (adduction).
The upper arm is a part of the upper extremity and consists of a bone, several muscles and other structures. The upper arm is connected to the trunk via the shoulder joint. This joint makes the entire arm very flexible.
Towards the forearm the upper arm is connected to the elbow joint. The only bone on the upper arm is the humerus. Together with the glenoid cavity of the shoulder blade, this large tubular bone forms the shoulder joint.
This joint is stabilized by a capsule and several muscles. This group of muscles is called the rotator cuff because, similar to a cuff, it surrounds the shoulder joint and the muscles are responsible, among other things, for the rotational movement (rotation). These muscles include Another important muscle that starts at the upper arm is the biceps (Musculus biceps brachii).
This muscle has several functions and is responsible for movement in both the shoulder and elbow joints. The arm can be turned inwards, stretched forward, moved away from the body and bent at the elbow. The musculus brachialis is also responsible for bending the arm.
On the back of the upper arm there is the triceps muscle (Musculus triceps brachii). This stretches the arm in the elbow joint and is able to pull the arm back towards the body. The blood supply to the upper arm is ensured by the brachial artery, which in turn is divided into several branches.
Venous drainage is provided by several veins, such as the superficial basilica and cephalic veins. The two nerves, the musculocutaneous nerve and the radial nerve, motorize the muscles of the upper arm and sensitive areas of the skin. – the musculus teres minor, the musculus subscapularis,
- The musculus supra- and
Like the upper arm, the forearm belongs to the upper extremity. It is connected to the hand via the wrist and to the upper arm via the elbow joint. In contrast to the upper arm, two bones form the basis of the forearm, the ulna and the radius.
These two tubular bones are connected by a membrane, the Membrana interossea antebrachii. In addition, these bones together form a joint at the elbow and wrist, the proximal and distal radioulnar joint. The main movements that result from this joint are the pronation and supination of the forearm and wrist respectively.
The musculature of the forearm consists of many muscles, which can be divided functionally into the flexor and extensor muscles. The muscles that bend the hand can be further divided into the deep and superficial muscles. The deep muscles include the muscle flexor digitorum profundus and the muscle flexor pollicis longus.
The superficial flexor muscles include a total of five muscles, for example the pronator teres muscle. There are also superficial and deep muscles in the extensor muscles. There is also another muscle group, the radialis group.
These muscles are responsible for the bending of the hand in the direction of the spoke. Blood is supplied by the arteria ulnaris and arteria radialis. These two vessels emerge from the brachial artery.
The numerous muscles are supplied by several nerves, such as the radial and ulnar nerves. The hand is a complex structure with many bones and muscles that allow great mobility. Its function is to grasp and hold objects, without which an independent life is not possible.
Via the wrist, the hands are connected to the forearm and thus form the last part of the upper extremity. The hand consists of a total of 27 bones, which makes up about a quarter of all human bones. There are eight carpal bones (scaphoid bone, moon bone, triangular bone, pea bone, large and small polygonal bone, head bone, hook bone), five metacarpal bones and 14 phalanges.
The fingers are composed of three small bones. An exception is the thumb, which consists of only two bones. Besides the many bones, there are 33 muscles that are involved in the great mobility.
Most of them have their origin at the forearm and pull with their tendons into the hand. The blood supply of the hand is ensured by the arteria radialis and the arteria ulnaris. The motor and sensitive supply of the hand is also provided by several nerves (radial nerve, ulnar nerve and median nerve). Depending on which nerve is injured, there are characteristic symptoms of hand failure, such as a drop hand. This gives an indication of damage to the radial nerve, which can, for example, be injured by a fracture of the humerus.