Radial nerve: what it is, where it passes through, and functions.

One of the branches of the nervous system that most influences sensory perception and movement.

Salute. Bends the wrist. Extend your fingers. You've probably been able to do this with ease. And that's because your brain has sent the relevant information to the muscles of your arm, wrist and hand to do so. This transmission has been carried out thanks to a series of nerves, which connect the rest of the nervous system with the muscles. One of them, of great importance for the movement and sensibility of the extremities, is the radial nerve. It is about this nerve that we are going to talk about next.

The radial nerve: description and location

The radial nerve is one of the most important nerve fiber bundles in the control of the upper extremities, being a peripheral nerve of the autonomic nervous system. peripheral nerve of the autonomic nervous system..

It is one of the three main nerves that innervate the upper extremities, together with the ulnar and median nerves.

The radial nerve innervates muscles as relevant as the triceps or the anconeus, or the brachial and brachioradialis. Also, among others, the extensors of the fingers, including the index finger and thumb. It is therefore a nerve of great relevance for the human being. But not only that, it also has connections with the cutaneous nerves and allows sensitivity and tactile perception in the area it innervates.

Areas through which it passes and its two main branches.

The nerve in question arises from the brachial plexus, just behind the axillary artery.. It then proceeds through the axilla and then down the arm and forearm, hands and fingers. It should also be noted that there are two radial nerves, one in each of the halves of the body.

It passes through the anterior compartment of the arm, passing around the spiral groove of the humerus (whose breakage could affect the nerve) and after that it crosses the elbow and reaches the forearm, where it will divide into a superficial and a deep branch.

The deep branch passes through the supinator muscle, entering the forearm and reaching the wrist posteriorly. This branch is linked to Muscle perception and the tension and extension capacity of the innervated muscles.

The superficial branch of the radial nerve acts at skin level, affecting the sensitivity of the upper extremities.. This is subdivided into three cutaneous nerves: posterior arm, posterior forearm and lateral arm. It also reaches the hand. This branch allows cutaneous perception of the back of the forearm, the upper arm, the back of the hand and the first four fingers.

Functions of this nerve

Our arms and especially our hands are fundamental elements for the human being since thanks to them we can develop a great amount of activities, from defending ourselves or eating to elaborate instruments and complex technologies. Its control is therefore of great importance.

The functions of the radial nerve in this regard are very broad, and it is interesting to note that it it plays a role in both sensory perception and motor control..

At the sensory level it allows sensitivity and perception of the back of the arm and forearm, including elbows and wrists, as well as part of the hand (specifically allows sensitivity of the back of the hand) and most of the fingers (except the little finger and part of the ring finger).

At the motor level, it allows the extension of the fingers, wrist and arm. Its action is especially relevant in the posterior forearm, as it innervates the muscles of the forearm.by innervating the muscles of the posterior compartment (which allows extension of the wrist and fingers) and the upper arm (by innervating the triceps brachii).

Injuries to the radial

Seen in a general way the functions of this nerve, it can be easy to guess the effects that its injury can have: the loss of sensibility in a great part of the posterior area of the arm, in the back of the hand and even in the fingers and loss of the ability to perform a large number of movements..

If this nerve is injured at the level of the axilla, the ability to extend the arm, wrist or fingers is lost, remaining the triceps and the rest of innervated muscles paralyzed, as well as the tactile perception of much of the arm and the back of the hand.

In the event that the injury is at the level of the humerus, there will be a decrease in the strength of the triceps and the wrist and fingers cease to be able to extend and the perception of the back of the hand, wrist and back of the forearm will disappear. It is also generally called wrist drop, which results in loss of coordination and difficulty in closing the hand.

If the lesion occurs at the level of the superficial branch, the ability to move the entire area will remain intact, but the sensitivity of the wrist, hand and fingers will be lost.

These alterations can occur due to a great number of factors, and can be produced by either due to lacerations and injuries, impingement or myelination problems. Examples of elements that can cause them are neuropathies such as diabetic, fractures of the humerus or radius, dislocations, intoxication, pressure on the wrist, continuous enchantment and lack of movement or inflammation.

Bibliographic references:

• Brazis, P., Biller, J. & Masdeu, J. (Eds) (2007). Peripheral Nerves. In: Localization in Clinical Neurology: 27-72. Philadelphia: Lippincott Williams & Wilkins.
• Ricci, F.P., Barbosa, R.I., Elui, V.M., Barbieri, C.H., Mazzer, N. & Fonseca, M.C. (2015). Radial nerve injury associated with humeral shaft fracture: a retrospective study. Acta Ortop Bras, 23(1):19-21.