Radial Nerve

Generality

The radial nerve is an important peripheral nerve of the upper limbs, which originates from the so-called brachial plexus and runs through the whole arm and then the forearm.

Having both a motor function and a sensory function, the radial nerve contains the nerve fibers of the spinal roots C5, C6, C7, C8 and T1. Along the way, the nerve in question gives rise to various branches (or branches): the so-called posterior cutaneous nerve of the arm, the branches that innervate the triceps brachialis muscle, the inferior lateral cutaneous nerve of the arm, the posterior cutaneous nerve of the arm, the deep branch of the radial nerve and the superficial branch of the radial nerve.

The radial nerve can be the victim of injuries, which can alter the sensory or motor functions of the nerve in question.

Short review of what a nerve is

To fully understand what a nerve is, it is necessary to start from the concept of neuron .

Neurons represent the functional units of the nervous system . Their task is to generate, exchange and transmit all those (nervous) signals that allow muscle movement, sensory perceptions, reflex responses and so on.

Typically, one neuron consists of three parts:

  • The so-called body, where the cell nucleus resides.
  • Dendrites, which are equivalent to receiving antennae for nerve signals from other neurons or receptors located in the periphery.
  • Axons, which are cellular extensions having the function of spreading the nervous signal. The axon covered with myelin (myelin sheath) is also called nerve fiber.

A bundle of axons forms a nerve .

Nerves can carry information in three ways:

  • From the central nervous system (CNS) to the periphery . The nerves with this property are called efferent. The efferent nerves control the movement of the muscles, so I am in charge of the motor sphere.
  • From the periphery to the CNS . Nerves with this capacity are called afferent. Nervous patients report to the CNS what they detected in the periphery, therefore they cover a sensitive (or sensory) function.
  • From the SNC to the periphery and vice versa . Nerves with this double capacity are called mixed. Mixed nerves have a dual function: motor and sensory.

What is the radial nerve?

The radial nerve is an important peripheral nerve of the upper limbs, having both a sensory function and a motor function.

The radial nerve is one of the five main nerve structures, which derive from the so-called brachial plexus . The brachial plexus is an important reticular formation of several spinal nerves (which are nerves of the peripheral nervous system ), which have the task of innervating not only the shoulder, but also the entire upper limb (therefore arm, forearm and hand) .

In addition to the radial nerve, the other 4 main nerve structures, which derive from the brachial plexus, are: the musculocutaneous nerve, the axillary nerve, the median nerve and the ulnar nerve .

Anatomy

The radial nerve is a continuation of the posterior cord of the brachial plexus.

The posterior cord of the brachial plexus comprises the nerve fibers of the spinal roots C5, C6, C7, C8 and T1 (NB: to better understand what the spinal roots are, readers are advised to read the article here). This means that, in the radial nerve, there are nerve fibers belonging to all the aforementioned spinal roots.

Along its entire course, the radial nerve gives rise to several branches, which are called branches .

ORIGIN AND COURSE OF THE MEDIAN NERVE

The point of the upper limb where, from the brachial plexus, the radial nerve is born is the armpit .

From here, the radial nerve descends along the arm, first occupying a posterior position, with respect to the humerus (arm bone), then a lateral position and, finally, an anterior position. In other words, first it resides in the back section of the arm, then it moves into the lateral section and, finally, it moves into the front department.

When moving laterally to the arm bone, the radial nerve is inserted into a deep lateral groove of the humerus; this groove is called radial groove .

For much of his path along the arm, the radial nerve runs near a branch of the brachial artery.

Flanked, for most of his path in the arm, by the brachial artery, the radial nerve enters the forearm immediately after having positioned itself anteriorly, with respect to the humerus. The entrance to the forearm, by the radial nerve, occurs at the so-called cubital fossa .

In the forearm, the radial nerve separates into two: in the deep branch of the radial nerve and in the superficial branch of the radial nerve .

The deep branch of the radial nerve is a nerve branch with motor functions; the superficial branch of the radial nerve, on the other hand, is a nerve branch with sensitive functions.

BRANCHE OF THE RADIAL NERVE

Two of the radial nerve branches have already been named: we are talking, of course, about the deep branch of the radial nerve and the superficial branch of the radial nerve.

The other branches are:

  • The branch called the posterior cutaneous nerve of the arm . It originates around the axilla;
  • The branches that point towards the long head (or long head) and the medial head (or medial head) of the brachial triceps . These branches originate from the radial nerve tract that passes behind the humerus;
  • The branch heading towards the lateral head (or lateral head) of the brachial triceps . This branch originates from the radial nerve tract that passes laterally to the humerus;
  • The branch called the lower lateral cutaneous nerve of the arm . It originates in the arm;
  • The branch called the posterior cutaneous nerve of the forearm . It originates in the posterior region of the arm.

Functions

As stated at the beginning, the radial nerve fulfills both motor functions and sensitive functions.

MOTOR FUNCTIONS

The radial nerve innervates muscles located in the arm and forearm:

  • In the arm, innervates the three heads (or heads) of the muscle called triceps brachialis. The triceps brachialis muscle belongs to the posterior region of the arm; originates in three distinct points, with the so-called heads (long, medial and lateral), and ends on the olecranon of the ulna and on the joint capsule of the elbow .

    The triceps brachial muscle allows elbow extension and represents the main muscular element of the posterior arm compartment.

    The innervation of the heads of the triceps brachialis muscle belongs to the radial nerve branches, which originate in the radial nerve tract posterior to the humerus and in the lateral radial nerve tract to the humerus.

  • In the forearm, it innervates the muscles of the posterior compartment. The muscles of the posterior compartment of the forearm are, for the most part, extensor muscles of the hand. Their job is to allow the extension of the wrist and fingers.

    The innervation of the muscles of the posterior compartment of the forearm lies, above all, with the deep branch of the radial nerve; deep branch that, at a certain point of its journey, becomes posterior interosseous nerve .

Summary of the muscles innervated by the radial nerve and its branches, at the level of the forearm:
Deep radial nerve branch
  • Short radial extensor of the carpus
  • Supinator muscle
Posterior interosseous nerve
  • Extensor muscle of the fingers
  • Extensor muscle of the little finger
  • Extensor ulnar carpus muscle
  • Long abductor muscle of the thumb
  • Short extensor muscle of the thumb
  • Long extensor muscle of the thumb
  • Extensor index muscle

SENSITIVE FUNCTIONS

The sensory functions of the radial nerve belong to the branches known as: posterior cutaneous nerve of the arm, inferior lateral cutaneous nerve of the arm, posterior cutaneous nerve of the forearm and superficial branch of the radial nerve.

  • Posterior cutaneous nerve of the arm : provides innervation and cutaneous sensitivity of the posterior region of the arm;
  • Lower lateral cutaneous nerve of the arm : provides for the innervation and cutaneous sensitivity of the lateral region of the arm. To be precise, the affected skin region is just below the deltoid muscle;
  • Posterior cutaneous nerve of the forearm : provides innervation and cutaneous sensitivity of the posterior and central region of the forearm;
  • Superficial radial nerve branch : provides for the innervation and cutaneous sensitivity of the dorsal surface of the thumb, index, middle and half ring.

diseases

The radial nerve can be injured. Radial nerve injuries are injuries that can affect both motor and sensory nerve function in question.

The episodes of lesion of the radial nerve can take place in at least 4 different points: at the level of the tract with seat in the axilla, at the level of the tract that passes through the radial groove, at the level of the deep branch of the radial nerve and, finally, at level of the superficial branch of the radial nerve.

LESION OF RADIAL NERVE WITH SEAT IN THE ARMCHAIR

Lesions of the radial nerve tract located in the axilla can be the result of a dislocation of the humerus from the glenohumeral joint (a shoulder joint) or a fracture of the proximal portion of the humerus .

Under the motor aspect, the effects are: paralysis of the brachial triceps and forearm muscles. The affected subject, therefore, is unable to extend the forearm, wrist and fingers of the hand.

Under the sensitive aspect, instead, the main effect is the loss of cutaneous sensitivity in all four portions innervated by the sensitive branches.

LESION OF THE RADIAL NERVE WITH SEAT IN THE RADIAL GROOVE

As a rule, lesions of the radial nerve tract passing through the humeral groove are the consequences of fractures on the body of the humerus . The body of the humerus is the central region of the humerus, the one between the proximal end and the distal end.

Under the motor aspect, the effects consist in a weakening of the brachial triceps (never paralysis!) And in the paralysis of the posterior muscles of the forearm. The affected subject, therefore, is unable to extend the wrist and fingers.

From the sensory aspect, however, the main effect is the loss of cutaneous sensitivity in the portions of skin innervated by the superficial branch of the radial nerve. Readers are reminded that the superficial branch of the radial nerve provides the sensory perception of the dorsal surface of the thumb, index, middle and half ring.

INJURIES OF THE DEEP BRANCA OF THE RADIAL NERVE

The lesions of the deep branch of the radial nerve can be the consequence of fractures of the so-called radial head or of posterior dislocations of the radium, with respect to the elbow joint.

Under the motor aspect, this type of injury affects the functioning of the muscles of the posterior compartment of the forearm, with the exception of the supinator muscle and the long radial extensor muscle of the carpus.

In the sensitive aspect, on the other hand, the lesions of the deep branch of the radial nerve do not produce any effect, since - as will be recalled - the branch in question lacks a sensory function.

INJURIES OF THE SURFACE BRANCA OF THE RADIAL NERVE

Lesions of the superficial branch of the radial nerve may be the result of cuts (eg: stabbings) or lacerations of the forearm .

From the sensory aspect, this type of injury eliminates the cutaneous sensitivity of the dorsal surface of the thumb, index, middle and half ring.

Under the motor aspect, however, it does not cause any effect, since - as will be recalled - the superficial branch of the radial nerve has only a sensory function.

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