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Median Nerve

What Is It, Location, Innervation, Damage, and More

Author: Alyssa Haag

Editors: Ahaana Singh, Lisa Miklush, PhD, RN, CNS

Illustrator: Jillian Dunbar

What is the median nerve?

The median nerve is a sensory and motor nerve of the arm (or upper limb). It arises from the lateral and medial cords of the brachial plexus, originating in the spinal cord, and runs through the anterior portion of the arm and forearm before finishing its path at the hand and digits (fingers). 

The median nerve innervates some of the major muscles of the forearm and hand, which allows for a two-way communication between the brain and spinal cord, and the muscles and overlying skin. The brain and spinal cord can send signals through the medial nerve, to the muscles that it innervates, with instructions on when to contract and complete specific actions. Similarly, the muscles and overlying skin can transmit sensations and sensory information, such as heat and pain, through the median nerve, and back to the brain and spinal cord for processing.

Where is the median nerve?

The median nerve spans the length of the upper limb. After arising from the lateral and medial cords of the brachial plexus, the median nerve enters the arm at the axilla (armpit). It then travels with the brachial artery down the shaft of the humerus bone and into the cubital fossa, which is on the surface of the elbow joint. From the cubital fossa, the median nerve traverses through the anterior forearm and will then pass through the carpal tunnel, which is a narrow passageway in the palm-side of the wrist. After reaching the hand, the median nerve innervates various muscles of the hand.

What does the median nerve innervate?

The median nerve innervates many muscles of the anterior forearm and hand, providing signals to and from the brain and spinal cord. The flexor digitorum superficialis and pronator quadratus are among the muscles of the anterior forearm that are solely innervated by the median nerve. They are involved in flexing and pronating the forearm and wrist. 

There are only two muscles of the anterior forearm that are not solely innervated by the median nerve: the flexor carpi ulnaris and flexor digitorum profundus. Instead, the flexor carpi ulnaris receives sole innervation from the ulnar nerve and the flexor digitorum profundus receives dual innervation from both the median and ulnar nerves. These muscles are also some of the major muscles involved in flexing and pronating the forearm and wrist.

Additionally, a branch of the median nerve, referred to as the “recurrent branch of the median nerve”, innervates the muscles of the thenar eminence of the hand. The thenar eminence contains the palm muscles at the base of the thumb. Thenar muscles enable thumb opposition, abduction and adduction. Distal branches of the median nerve also supply innervation to the lumbrical muscles located in the index and middle fingers.

What happens if the median nerve is damaged?

The median nerve is usually damaged at either the elbow, due to a fracture of the humerus bone of the upper arm, or the wrist, due to either carpal tunnel syndrome or a wrist laceration or gashing. If the median nerve is damaged at the elbow region, it is known as a proximal injury to the median nerve. Proximal injury to the median nerve often presents with the hand of benediction, a sign that occurs when an individual is unable to make a complete fist. This occurs because flexion of the finger joints, specifically the first and third finger joints (the metacarpophalangeal and distal interphalangeal joints, respectively) of the 1^st and 2^nd fingers, are lost with median nerve damage. Consequently, when an individual with such nerve damage attempts to make a fist, the thumb and first two fingers remain partially distended, resembling the hand gesture of a Pope as he gives blessings, hence, the name “hand of benediction”.

If the median nerve is damaged at the wrist, this injury is called a distal injury to the median nerve. The most common cause of medial nerve injury at the wrist is carpal tunnel syndrome (CTS), although a wrist laceration may also cause injury to the median nerve. 

CTS occurs due to a pinched median nerve in the wrist, and is often associated with pain, tingling, and numbness in the hand and arm. The median nerve becomes compressed due to entrapment between the transverse carpal ligament and carpal (also known as the wrist bones). The root cause of carpal tunnel syndrome can be attributed to a variety of conditions, including inflammation from repetitive use (e.g. excessive computer use), infection, pregnancy, diabetes mellitus, and hypothyroidism. Carpal tunnel syndrome can cause atrophy, or wasting, of the muscles in the thenar eminence due to a lack of stimulation from the median nerve and the resulting inability to properly function. Prolonged periods without stimulation may cause the muscles of the thenar eminence to waste away. In some cases, this can result in the inability to oppose the thumb and may cause a condition known as ape hand. Ape hand is characterized by the severely limited ability to move the thumb.

How do you stretch the median nerve?

In order to exercise and improve the movement of the median nerve, it can be stretched. To stretch the median nerve, an individual can place their palm flat on the wall with their fingertips pointing away from their body and parallel to the floor. Rotating the body away from the arm while keeping the elbow straight will then result in a stretch in the arm and forearm.

Stretching the median nerve, and nerves in general, can help improve their movement through the joints and muscles by improving their ability to slide and glide. Nerves, just like muscles, can become tight if in the same position for an extended period of time and nerve stretching can assist in reducing tightness and relieving pain.

How do you diagnose and treat median nerve compression?

Clinical presentation of symptoms and physical examination are used to diagnose median nerve compression. For instance, a physical exam may confirm diagnosis through the help of the Tinel sign and Phalen maneuver. The Tinel sign is positive if tingling is experienced when pressure is applied to the wrist. The Phalen maneuver is positive if tingling is experienced when the wrist is placed at a 90° angle. With median nerve injury, specifically due to CTS, both the Tinel sign and Phalen maneuver will likely be positive. 

When treating median nerve compression, splinting is considered a first-line treatment. Other conservative, or traditional, treatments can include physical therapy, yoga and therapeutic ultrasound. Therapeutic ultrasound uses ultrasound technology to speed up the rate of healing and enhance the quality of repair. In some cases, oral steroids or the injection of steroids may also be considered for severe pain relief. Individuals with CTS may also be advised to make ergonomic adjustments to their workspace and computer space, such as wrist and elbow supports to help relieve pain. 

Patients with severe pain of more than four to six months and no relief from conservative treatments may be offered surgical decompression.

What are the most important facts to know about the median nerve?

The median nerve is a major nerve of the upper limb as it innervates the major muscles that enable an individual to flex their wrist and fingers, and oppose their thumb. If the median nerve is damaged, an individual may present with the sign of benediction due to the lost ability to flex their thumb and first two digits. An individual may also experience ape hand due to the loss of thumb opposition. After diagnosis through physical examination, splinting is considered the first line treatment for medial nerve injury and surgery may be an option if pain remains persistent.

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