Radial nerve
The radial nerve is composed of the posterior nerve roots of the plexus and formed their direct continuation. It pulls forward along the back of the arm along the humerus. At the level of the crook of the arm it comes forward again and finally runs along the back of the forearm on the side of the thumb to the hand.
Once it reaches the thumb, the radial nerve branches out into its sensitive end branches. On the hand, it provides sensitive care, especially in the thumb area and partly also on the back of the hand. It passes its motor branches on to the muscles of the upper and lower arm as it progresses.
Thus, this hand nerve innervates the extensor muscles of the upper arm and the extensor muscles of the thumb. In the case of fractures or other injuries in the area of the humerus, the radialis nerve is particularly at risk because of its close proximity to the bone. If it is injured, complaints such as sensitivity disorders and motor deficits occur.
The disturbance of the motor function manifests itself as a so-called drop hand. The hand nerve is responsible for the extensor muscles when intact. If it is now limited in its function, it can no longer lift the hand and the hand falls limply.
Ulnar nerve
After the ulnar nerve has left the plexus of the arm, it moves along the side of the upper arm that is directed towards the body. It wraps itself around the elbow bone and finally pulls along the forearm to the wrist on the side facing the little finger. Just before the retinaculum musculorum flexorum, the hand nerve splits into a superficial and a deep branch.
Already during its course through the forearm, it innervates muscles lying there. In the hand, it is responsible for the motor innervation of some of the muscles of the ball of the thumb and the muscles of the ball of the little finger. It also supplies the muscles of the metacarpus.
The innervation of these muscles enables the spreading and closing of the fingers. Sensitively the hand nerve supplies the skin over the little finger and half of the adjacent ring finger.In the area of the elbow, the nerve runs through an easily palpable channel, the sulcus nervi ulnaris. Here, the hand nerve runs directly under the skin and is in close contact with the underlying bone.
The superficial position of the nerve can quickly cause sensations of discomfort through light impact. This symptomatology is known to most people as muscular bone. If the hand nerve is damaged by a fracture or a dislocation in the area of the elbow joint, the symptoms of a claw hand often occur.
The hand muscles lose their ability to spread the fingers because they are no longer properly innervated by the ulnar nerve. The fingers of the affected hand remain in a bent position and are therefore called the claw hand. In addition to the motor disorders, there are also additional sensitive failures. These particularly frequently affect the skin over the little finger and ring finger.
