The Anatomy of the Ulnar Nerve

The Nerve That Runs Through Your "Funny Bone"

In This Article

The ulnar nerve controls sensation and movement in sections of the arm and hand. It is best known for its location as it runs through the “funny bone” in the elbow. When your ulnar nerve is bumped in this spot, it causes an electric shock sensation down your arm and hand that most people have experienced at least a few times. 

This nerve can become impaired due to traumatic injury or overuse of the arm. Often, symptoms of overuse resolve with rest, but serious injuries may require surgical intervention. While it is rare, weakness or sensory loss can remain for the long term.

Anatomy

The ulnar nerve is a long nerve, running through the whole arm. Throughout its pathway from the shoulder down to the hand, it divides into several motor and sensory branches.

Structure 

This nerve is one of the branches of the brachial plexus, and it arises from the C8 and T1 nerve roots. The ulnar nerve gives off several small branches along its path as it continues to travel through the arm. 

  • Its first two branches are two motor nerve branches, in the arm. 
  • A few inches above the wrist, the nerve divides into the palmar cutaneous branch and the dorsal branch. 
  • The superficial branch, deep branch, and the digital branches are in the hand. 

Articular branches are nerves around joints. They are found throughout the body. The ulnar nerve has an articular branch in the elbow and another at the wrist. 

Location

The ulnar nerve can be found deep underneath muscles in the arm, but it is relatively superficial at the elbow, where it runs along a bone called the medial epicondyle. It is most exposed at this area along the medial epicondyle, lying underneath the skin, without bony or muscular protection. 

The nerve runs through the cubital tunnel at the elbow and passes through the Guyon tunnel in the wrist. Its branches extend into the lateral (towards the pinky finger) side of the palm, the lateral side of the back of the hand, the pinky finger, and the lateral half of the ring finger.

Function

The ulnar nerve is involved in carrying sensations from the hand and fingers up to the spinal cord. This nerve also controls the movement of several muscles in the arm and hand.

Motor

Small motor branches of the ulnar nerve supply muscles that move areas of the hand and fingers.

  • The flexor carpi ulnaris in the arm flexes the hand.
  • Part of the flexor digitorum profundus in the arm flexes the pinky finger and ring finger.
  • Small motor branches of the ulnar nerve in the hand move the pinky finger and ring finger and help you spread your fingers. 

Sensory

The sensory branches of the ulnar nerve relay sensation from:

  • The dorsal cutaneous branch carries sensation from the back of the pinky finger and half of the back of the ring finger.
  • The palmar cutaneous branch carries sensation from the lateral portion of the palm directly near the pinky finger.
  • The superficial branch carries sensation from the front of the pinky finger and half of the ring finger.

Associated Conditions

There are several conditions that can affect the ulnar nerve. Early symptoms include paresthesias (unusual or unpleasant sensations) of the pinky finger, half of the ring finger, and the lateral portion of the hand. These conditions can eventually result in weak wrist flexion and/or diminished strength of the pinky or ring finger.

Funny Bone Irritation

A small bump in the elbow can cause a sudden electric shock sensation that lasts for a few seconds.

This is not a pleasant sensation, but it is called “funny” because the ulnar nerve runs along a bone called the humerus.

Cubital Tunnel Syndrome

Compression of the ulnar nerve causes cubital tunnel syndrome. If you have swelling of the areas near your elbow, you can experience paresthesias, pain, diminished sensation, or decreased muscle control in the areas of the hand that are supplied by the ulnar nerve. This usually occurs due to overuse, such as with typing or repetitive physical work.

Guyon's Canal Syndrome

Guyon’s canal syndrome is also called ulnar tunnel syndrome. You can have swelling in the wrist around the ulnar nerve as it reaches the hand. This can also occur due to overuse, and is most commonly associated with biking. 

Thoracic Outlet Syndrome

Thoracic outlet syndrome is a condition that is caused by pressure in the neck. This situation compresses the nerves of the brachial plexus, affecting the function of the ulnar nerve.

Trauma

Trauma in the arm or hand can cause damage to the ulnar nerve or any of its branches, affecting its function.

Testing Ulnar Nerve Function

There are a few quick ways of testing the ulnar nerve function.

  • Fromet’s sign is a test in which your doctor asks you to grasp a paper between your thumb and forefinger. Ulnar nerve weakness may cause you to be unable to hold on to the paper as it is pulled from you or may result in flexion of your thumb as you hold onto the paper, compensating for your weakness.
  • Tinel’s sign is a diagnostic test in which your doctor taps on your nerve in the suspected area of compression (the wrist or elbow). If your symptoms, such as tingling or pain recur, then the area that was tapped is the area of nerve compression.
  • Claw sign is a description of a claw-like flexion of the hand, which results from weakness of the hand muscles that are supplied by the ulnar nerve. Claw hand is usually accompanied by muscle atrophy in the hands. Atrophy is thinning of the muscles that can occur as a result of the inability to use them (in this case, because of the nerve impairment). 

Rehabilitation

If you have compression of your ulnar nerve, you can experience recovery if it is treated early, before permanent damage occurs. 

Resting your arm or hand and avoiding the damage-inducing physical movements is usually recommended to prevent continued overuse. Often, ice applied to the area of overuse can help diminish inflammation.

A splint is often recommended, particularly at night. This is because it is very common to flex the arm or wrist at night. Flexing stretches the ulnar nerve, but a splint can inhibit stretching it.

Be sure to talk to your doctor or therapist before using a splint so that you can use it correctly. A tight splint can cause additional damage.

Anti-inflammatory medications, including Advil (ibuprofen) and Aleve (naproxen), can help decrease inflammation around the nerve. 

Physical therapy or occupational therapy may be helpful if you have muscle atrophy or if you need to rebuild your muscle control. 

Surgery may be necessary to relieve pressure on the nerve or to repair nearby structures if you have experienced a traumatic injury. After surgery, you should expect to have physical therapy or occupational therapy as you build up strength and learn how to regain muscle control.

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