Anatomy-Lexicon

Radial nerve

Synonyms

Radial nerve

Medical: Radial nerve

English: radial nerve

definition

The radial nerve is an important arm nerve. It is called the spoke nerve because its course is based on the spoke, one of the two forearm bones (ulna and radius).
Like the other two main arm nerves (elbow nerve and median arm nerve), it consists of fibers that transport sensitive information from the skin and joints to the spinal cord and brain (sensitive afferents) and from motor fibers that send impulses from the brain to the arm muscles (motor efferents).

origin

The Radial nerve is one of many nerves from the arm nerve plexus, the Brachial plexus , together.
The spinal nerves from the cervical cord of the Spinal cords (C5-C8) assemble directly after exiting the spinal cord to form this bundle of nerves, which is called Arm nerve plexus (Brachial plexus) referred to as.
All the nerves that supply the arm emerge from this bundle of nerves.
The nerves of the Nerve cord bundle (Brachial plexus) be called:

Short branches:
N. subscapularis, N. thoracodorsalis, Nn. pectoralis medialis and lateralis, N. cutaneus antebrachii medialis, Nn. intercostobrachiales;

Long branches:
Musculocutaneous nerve, axillary nerve, radial nerve, median nerve, ulnar nerve

Overview and classification

A nerve contains fibers that transport sensitive impulses from the skin and joints back to the brain (Afferents) and at the same time fibers that send impulses from the brain to the muscles (Efferents).
A peculiarity of the radial nerve compared to its sibling, the median arm nerve (Median nerve) and the ulnar nerve (Ulnar nerve) is that it supplies muscles in both the upper arm and the forearm.

Anatomy and course

The spoke nerve (Radial nerve) runs from the armpit, where it arises from the plexus of the arm nerves, over the back of the humerus. There, during development, it notches a pit in the bone, the radial nerve pit (Radial sulcus). He pulls over the back of the elbow in the radial tunnel. Below the elbow, the nerve divides into two branches: a deep branch and a superficial branch (ramus profundus, ramus superficialis).
Whereby the deep branch its course through one of the forearm outward turning muscle (M. supinator) formed muscle channel (Supinator canal) takes.
The superficial branch pulls along the spoke (hence the name) protected by forearm muscles to the thumb and back of the hand.

On the long way from the root to the back of the hand, the spoke nerve repeatedly gives fibers / branches to muscles (motor branches) or on the skin (sensitive branches) from.

physiology

Motor skills

The Radial nerve is responsible for the activation of some muscles in the upper arm, forearm and hand and thus for the extension of the elbow joint, the pulling of the arm to the upper body (Adduction in the shoulder joint), overstretching the wrist towards the back of the hand (Dorsiflexion), Spreading the fingers, turning outwards (Supination) of the forearm.
The most important muscles supplied are:

Three-headed upper arm muscle (M. triceps brachii): Extension of the elbow joint;
Upper arm radial muscle (M. brachioradialis): Outward rotation (supination) of the forearm, flexion in the elbow joint;
Finger extensor (M. extensor digitorum): Extension of wrists and fingers;
Outward turning muscle (M. supinator): Outward rotation of the subname;
Long thumb spreader (M.abductor pollicis longus): Splaying the thumb.

Other muscles supplied by the radial nerve:

Little finger extensor (M. extensor digiti minimi)
Thumb extensor (M. extensor pollicis)
Index finger extensor (M. extensor indicis).

sensitivity

The skin on the side of the upper arm and the back of the forearm becomes sensitive to the skin Radial nerve/ Spoke nerve supplied. Half of the back of the hand (thumb, index finger, half of the middle finger) also belongs to the sensitive supply area of the nerves. This does not include the phalanges of the index and middle fingers, these are supplied by the sibling nerve Median nerve, the median arm nerve.

damage

"Crutch paralysis": the radial nerve (radial nerve) is pressed off in the armpit, for example when using crutches. Then there is no extension in the elbow joint and extension in the wrist ("drop hand"). The feeling on the upper and lower arm is missing.

If the upper arm breaks, the nerve can be injured on its way around the upper arm (nerve lesion). The elbow can then still be stretched, otherwise all functions are missing, as in "crutch paralysis".

If there is only pressure on the nerves in the radial nerve pit on the upper arm, it is called "park bench paralysis". In most cases, this disappears again.

If the passage through the external torso muscle is narrowed (Supinator canal), there is also a "falling hand" and impairment of the sensation on the forearm. This damage is known as supinatorlogic syndrome.

Read more on the subject at: Supinatorlous syndrome

If other nerves are damaged in addition to the radial nerve, complete brachial plexus paralysis can also occur.

Radial Nerve Syndrome

A Compression syndrome of a peripheral nerve such as the radial nerve arises from chronic pressure damage. For every nerve there are anatomically particularly endangered areas where the nerve is easily damaged.

If the radial nerve is damaged, the sensitivity in its innervation area is impaired, i.e. the area of the skin that is supplied by the radial nerve. So it can be on the Back of the hand of the thumb and index finger to Numbness, Pins and needles or pain. These symptoms are also on the ventral side of the forearm, i.e. the side that merges into the palm of the hand. Especially the transition to the thumb (radial forearm) is affected.

Since the radial nerve mainly supplies the extensors of the upper extremity (M. triceps brachii, M. brachioradialis, M. supinator, hand and finger extensors), a failure of the radial nerve results in what is known as a failure of the radial nerve Drop hand. Due to the failure of the extensors, the hand and fingers hang limply in the wrist.

Depending on the exact level at which the lesion of the nerve is located, some of the described deficits apply and others do not. The doctor can use this to diagnose the exact location of the nerve damage. He differentiates between a proximal and a distal lesion (e.g. in the case of a humerus fracture), as well as a supinatorlogic syndrome and lesions of the purely sensitive superficial branch.

Under the Wartenberg Compression Syndrome one understands pressure damage to the sensitive branch of the radial nerve. This leads to sensory disturbances without muscle weakness occurring. Wristwatches, plaster casts or handcuffs that are too tight can be the cause. The sensory disturbances (numbness, tingling or pain are possible) are on the back of the thumb and index finger, and the skin between the two fingers is also affected.

Entrapment of the radial nerve

Nerves are extremely sensitive when they are pinched. In the upper extremities in particular, many important nerves run in a relatively small space. In certain places, the risk of the nerve becoming trapped between muscles, tendons, soft tissue and bony structures is particularly great. The radial nerve is a mixed sensory and motor nerve, which means that it is responsible for feeling (sensitivity) and voluntary muscle contractions (movements) in certain areas of the arm and hand.
It should be noted that only the part of the arm or hand that is distant from the damaged area is affected by functionality failures. If there is damage to the nerve in the area of the wrist, this can lead to sensory disturbances and muscle weakness in the area of the hand and fingers, but never to failures in the area of the upper arm or forearm.

Common causes for pinching the radial nerve Accidents or pressure lesions, as well as slowly developing bottlenecks due to an increase in muscle mass or soft tissue.
Medical treatments (e.g. positioning during surgery, plaster casts or injections) can also pinch the radial nerve.