Ulnar Nerve: Structure, Function & Diseases

The ulnar nerve is one of the nerves of the brachial plexus and is responsible for important motor and sensory functions of the hand. It is a long nerve, which extends over the entire arm to the hand. Damage to the ulnar nerve results in hand numbness and even loss of function with paralysis.

What is the ulnar nerve?

Within the brachial plexus, the ulnar nerve is connected to the spinal cord by nerve fibers. These fibers originate in the 8th segment (C8) of the spinal cord, which is located between the seventh cervical and first thoracic vertebrae. Thus, via the ulnar nerve, sensitive signals are sent from the skin to the brain via the spinal cord and, conversely, impulses are sent from the brain to the supplying muscles. The ulnar nerve, also known as the ulnar nerve, provides impulse transmission to special muscle groups of the arm] and hand muscles, which are responsible for flexion and fine motor skills of the hand and fingers. The preceding sensory impulse signals the brain which muscle groups to activate. Damage to the ulnar nerve therefore leads, in extreme cases, to paralysis and muscle loss in the hand.

Anatomy and structure

The ulnar nerve runs through the entire arm from the upper arm to the elbow to the forearm and splits even further in the hand. It is a component of the brachial plexus. The brachial plexus is a nerve cord formed by the confluence of spinal cord nerves from the cervical medulla of the spinal cord. The brachial plexus is the origin of all the nerves that supply the arm. It contains short and long branches. The ulnar nerve is one of the long branches of the brachial plexus. Initially, the ulnar nerve runs from the axilla across the inside of the upper arm to the elbow. There, it breaks through the muscular skin on the medial side of the upper arm and moves behind the bony prominence of the elbow to the anterior inner side of the forearm. In the region of the humerus, the ulnar nerve is unprotected and can cause severe pain when impacted. This pain reaction is colloquially known as funny bone. In the forearm, the nerve is protected by a forearm muscle. Above the carpal tunnel, it then runs to the palm. In front of the wrist, the ulnar nerve splits into the motor ramus profundus and the sensory ramus superficialis.

Function and Tasks

The ulnar nerve supplies the muscles involved in flexion of the wrist and flexion and abduction of the fingers. The nerve forms motor and sensory branches. These include the motor ramus profundus and the sensitive ramus superficialis. The motor branches transmit impulses from the brain to the corresponding muscles. This triggers the characteristic movements. There are different motor branches in the forearm as well as in the hand. In the forearm, three muscles are innervated that are necessary for hand and finger flexion. In the hand, muscles are stimulated that regulate flexion and abduction of the little and ring fingers. Overall, the ulnar nerve controls the tightening and flexion of the thumb; the spreading, extension, and flexion of the little finger; the flexion of the fingers at the base joint and the extension of the fingers at the terminal joint; the spreading of the fingers; and the flexion of the wrist. These movements are coordinated via the interaction of the brachial plexus, spinal cord and brain. Among other things, the sensitive branches of the ulnar nerve also ensure this. They transmit the sensory impressions of the skin to the brain via the spinal cord. The ulnar nerve is responsible for the sensitive areas of the edge of the hand with the little finger, the back of the hand up to half of the middle finger and the palm up to the middle of the ring finger.

Diseases and complaints

Damage to or irritation of the ulnar nerve can result in sensory disturbances or paralysis in the hand. The location at which the nerve is disturbed also plays a role. Common disorders of the ulnar nerve are ulnar groove syndrome and Loge-de-Guyon syndrome. Ulnar groove syndrome is produced by irritation of the nerve at the elbow. There, the ulnar nerve is unprotected and can be severely irritated even by impact or pressure. Symptoms include tingling and numbness of the little finger, ring finger and adjacent palm area.Motor disorders follow, whereby the little finger can no longer be spread. The muscles are no longer optimally supplied, so that in the worst case, muscle atrophy can also occur. This limits the overall mobility of the hand. Without treatment, complete paralysis of the hand with the formation of a so-called claw hand is possible. The causes of this disease are manifold. At the elbow, the nerve is often irritated by impact or permanent pressure. A bone protrusion or fracture can also be responsible. Other causes include wear and tear or congenital anatomical changes at the elbow joint. It should also be noted that the pressure damage develops over the long term. Only a permanent irritation leads to the disease. Another disease, the so-called Guyon-Logen syndrome, can also lead to similar symptoms. In this case, irritation of the ulnar nerve occurs at the wrist. However, in contrast to ulnar groove syndrome, the sensory loss on the back of the ulnar side of the hand is absent here. To treat ulnar nerve disorders, it is necessary to clarify the cause in each case through a thorough history and imaging procedures.