The ulnar nerve is one of three main nerves that serve the arm. Each of these nerves has specific areas of the arm and hand that they innervate—or activate. The exact area served by each nerve varies slightly between individuals, but they follow a basic pattern.
This information is very useful for different types of medical professionals. They can tell, according to your symptoms, which nerve is responsible for a specific problem.
We explore the ulnar nerve and answer the question “What does the ulnar nerve innervate?”. We also highlight some common ulnar nerve problems and discuss how pathologies of the ulnar nerve are diagnosed and treated.
What Is the Ulnar Nerve?
All nerves originate from the spinal cord. They branch off at certain points through the spaces between the vertebrae. The ulnar nerve is a long nerve that originates from the lower cervical spine.
It’s difficult to be more specific than this. All the nerve roots intertwine and separate again as they leave the spinal cord. They form a network known as the brachial plexus.
From the brachial plexus, the ulnar nerve tracks down the lower part of the inside of the arm. Smaller nerves branch off the main ulnar nerve at various points, innervating different structures.
In the upper arm, the ulnar nerve runs down into the compartment at the back. When it reaches the elbow, it passes through the ulnar groove behind the elbow.
When you bang your elbow, it’s actually the ulnar nerve that generates the most pain. The “funny bone” we all talk of—also known as the humerus—is more hardy than the nerve. At the elbow, the ulnar nerve passes through a small space between skin and bones. It has very little padding or protection.
The ulnar nerve pathway travels down through the forearm. At the wrist, the ulnar nerve runs superficially and medially—the same side as your little finger. It enters the hand through the ulnar (or Guyon’s) canal on the palmar surface.
The ulnar nerve runs right down to the fingers. It activates both sides of the hand in the area of the little finger, the ring finger and part of the middle finger.
Below is a link to an interesting video which gives a good explanation of ulnar nerve anatomy. It contains in-depth detail about the path of the ulnar nerve through the arm to the hand.
What Does the Ulnar Nerve Innervate?
Now we know the pathway the nerve takes, we can get down to specifics. Each peripheral nerve has sensory and motor functions. As the name suggests, the former sense changes within its particular distribution. The latter activates the muscles.
In the forearm, the ulnar nerve has three main branches. The muscular branch innervates two muscles in the forearm. The flexor carpi ulnaris handles wrist flexion, or bending, and adduction—sideways movement. The second muscle—flexor digitorum profundus—is responsible for flexing or curling the fingers.
The other two main branches of the ulnar nerve are sensory. The palmar cutaneous supplies the skin on the medial side of the palm. The dorsal cutaneous branch serves the medial aspect of the back of the hand.
As we travel into the hand, the ulnar nerve also innervates the two most medial lumbrical muscles and the medial interossei. These are all small muscles in the hand responsible for gripping, writing and all manner of other fine motor movements.
The hypothenar muscle group is located on the palm below the little finger. This consists of three muscles:
- Flexor digiti minimi
- Flexor digiti minimi brevis
- Opponens digiti minimi
These three muscles are specific to the movement of the little finger. They’re the reason little fingers can move very freely and independently.
Finally, adductor pollicis—also innervated by the ulnar nerve—is responsible for pulling the thumb back towards the palm of the hand. Make a star shape with your hand, then making a fist. Adductor pollicis is the main muscle pulling your thumb in to make a fist.
Ulnar Nerve Symptoms
Possible symptoms of ulnar nerve problems include:
Conditions Affecting the Ulnar Nerve
Nerve entrapment can occur almost anywhere in the body. However, scientific studies tell us that ulnar nerve entrapment is the second most common neurological problem in the upper limb. This can occur at the elbow, where it’s known as cubital tunnel syndrome, and in the forearm or the hand.
Ulnar nerve entrapment at the wrist can also happen; this is known as Guyon’s canal syndrome. It’s worth noting that these types of ulnar nerve pathologies have been known to occur following bony changes after a fracture.
Tardy ulnar palsy is a chronic condition that can also occur post-fracture. Through changes in bone or soft tissue, the nerve is forced to take a longer path than normal. This results in the nerve being overstretched and symptomatic.
Another cause of ulnar nerve symptoms can be related to a problem with the nerve roots in the neck. If the lower cervical nerve roots are irritated or “trapped,” it can result in pain, tingling, numbness and weakness anywhere along the nerve. This is known as a cervical radiculopathy.
Ganglions can be a problem for the ulnar nerve. Ganglions are benign pockets of swelling that can form from joint or tendon soft tissue. Depending on where they are located, they can cause ulnar nerve compression. Ulnar nerve compression due to a ganglion has been diagnosed via magnetic resonance imaging (MRI).
How Are Ulnar Nerve Problems Identified?
Thankfully, there are many ways to diagnose ulnar nerve problems. Firstly, there’s a specific pattern to symptoms that your doctor will be looking for. Pain is one symptom, but this can be misleading.
Problems with nerves often involve referred pain in a different area to where the problem is. Ask anyone with sciatica - that horrible leg pain which most often originates from a problem in the lower back.
When nerves aren’t happy, they often tingle, have altered sensation, or numbness. For an ulnar nerve problem, this strange or reduced sensation will be apparent on both the palm and the back of the hand, but only on the medial side of the hand, and usually involving only the middle, ring and little fingers.
A marked weakness in the muscles innervated by the ulnar nerve is also a potential sign. No muscle in the body is able to work without being zapped into action with an electrical signal from the nerve. If those signals aren’t getting through, the muscle will be unable to work, and will waste over time if the problem isn’t resolved.
Nerve Conduction Tests
If it’s not a straightforward, common pathology, neurologists can carry out nerve conduction tests. It is possible to check whether messages are being passed along the nerve, and to identify the specific region of the problem.
Physical therapists can conduct nerve tension tests, which are proven tools in diagnosing an ulnar nerve problem. Biomechanical specialists are also able to identify any particular areas where the nerve is not functioning normally.
Whatever the route for diagnosis, it’s essential to establish the exact cause of the problem. Without this, treatment may be ineffective.
What Kind of Treatments Are Available?
In general, the body is good at healing nerves. They have a very good blood supply, which equates to a rich incoming supply of nutrients for healing. If you are able to get to the root cause of the symptoms, conservative treatments can work very well in many instances.
Depending on the specific problem, there are lots of different treatments available. If the problem is at the wrist or the elbow, splints and supports are available for use during the day and at night. They can keep the affected area in a good position and help reduce pressure on the nerve.
Physical therapy can help by correcting posture to relieve symptoms, prescribing specific exercises and giving pain management advice.
Surgery is usually considered only as a last resort after all other options have been explored. Again, the type of surgery considered depends entirely on the problem.
Surgeons are able to re-route the nerve if necessary, shave a part of a bone or cut through some of the soft tissue to give the nerve more space.
The ulnar nerve is one of three main nerves that are essential to hand and arm function. It provides sensory information from specific parts of the medial side of the hand. It also activates several of the muscles responsible for grip, wrist and forearm movement.
There are many different problems that can affect the ulnar nerve. The symptoms can be very disturbing for the patient. However, they are often resolved with conservative treatments. The best news about problems affecting the ulnar nerve is that they usually resolve with the correct care. Surgery is often unnecessary.