3D Anatomy Model

Brachial Plexus Explained

Overview

The brachial plexus is an intricate network of nerves in the neck and shoulder that carries signals for movement and sensation from the spinal cord to the arms and hands. The brachial plexus consists of several parts: trunks, roots, cords, branches, and divisions.

All the nerves in the brachial plexus come from the spinal cord. Thus any severe brachial plexus injury affects the spinal cord as well.

Structure

Roots

Nerves originating from the neck portion of the vertebrae (cervical vertebrae) are known as cervical nerves. These nerves divide into 2 divisions that supply the front and the back of the body (anterior and posterior rami respectively).

The brachial plexus begins as roots of the cervical and thoracic anterior rami nerve fibers. It includes the fifth, 6th, 7th, 8th, and first thoracic vertebrae.

All of the brachial plexus roots combine to form brachial trunks as it proceeds down the neck.

Trunks

  • Upper trunk – forms due to a combination of fifth and 6th cervical vertebrae roots.
  • Middle trunk – forms from only the 7th cervical vertebrae root.
  • Lower trunk – forms due to the combination of the first and 8th cervical vertebrae roots.

All of these trunks are further divided into two divisions (dorsal and ventral). The dorsal division supplies the back of the upper limb, while the ventral supplies the front of the upper limb. The trunks divisions join to form brachial plexus cords.

Cords

  • Lateral cord – forms by the union of middle and upper trunks’ ventral division.
  • Medial cord – forms from the lower trunk’s ventral division. The medial cord forms from only one division, unlike other cords.
  • Posterior cord – forms due to the combination of all the dorsal divisions in all the brachial plexus trunks. This cord comes into existence due to three divisions

Nerve supply by the brachial plexus

Root Branches

The nerve roots of the brachial plexus have branches that supply muscles of the neck and shoulder:

  1. Dorsal scapular nerve.
  2. Long thoracic nerve.
  3. Phrenic nerve

Trunk branches

Branches of the trunks only originate from the upper trunk of the plexus, which gives off two further branches:

  1. Suprascapular nerve
  2. Subclavian nerve

Cord branches

Branches from the lateral cord
  • lateral pectoral nerve
  • musculocutaneous nerve
  • part of the median nerve
Branches from medial cord
  • medial pectoral nerve
  • medial cutaneous nerve of arm
  • ulnar nerve
  • part of the median nerve
Branches from the posterior cord

Other than the brachial plexus branches, the upper limb has innervation from other cervical nerve fibers

Diagram of brachial plexus. Illustration by Chris Talbot

Muscles supplied by the brachial plexus

  • The roots of brachial plexus give innervation to serratus anterior, levator scapulae, and rhomboid muscles.
  • The upper trunk gives off innervation to the subclavius, infraspinatus, and supraspinatus muscles.
  • The lateral cord innervates the pectoralis major and minor, coracobrachialis, Biceps brachii, and brachialis muscles.
  • The posterior cord supplies subscapularis, deltoid, teres minor, triceps brachii, anconeus, supinator, brachioradialis, and latissimus dorsi muscles.
  • The medial cord innervates the pectoralis, forearm and hand muscles.
Graphical representation of the brachial plexus in the context of the shoulder anatomy. Illustration by Alice Roberts.

Diseases associated with the brachial plexus

Several injuries of the brachial plexus account for different conditions as:

Erb’s paralysis

In the brachial plexus, there’s a point at the upper trunk referred to as the Erb’s point, it is where six nerves meet. Any injury to the upper trunk of the brachial plexus causes Erb’s paralysis. The mainly involved nerves in Erb’s paralysis are branches originating from the fifth and 6th cervical vertebrae.

The most commonly paralyzed muscles in this condition are deltoid, bicep brachii, brachioradialis, and brachialis muscles.

In Erb’s palsy, the arms tend to hang on the sides close to the body and are turned inwards such that the hand appears as if the individual is asking for a tip. This appearance is called the policeman’s or waiter’s tip appearance of the hands.

Serratus anterior nerve injury

Serratus anterior nerve is a branch of the brachial plexus. In serratus anterior nerve injury, a person cannot raise or flex their arm above 90 degrees or raise it overhead because the serratus anterior muscle is a major participant in this movement.

Causes of this injury include :

  • Sudden heavy shoulder pressure from above e.g. from a falling object.
  • Overuse of the serratus anterior muscle by repeated carrying heavy objects on the shoulders.

The most prominent feature of this injury is the winging of the scapula. Winging of the scapula is the abnormal prominence of the scapula bone. In the normal anatomical body, the scapula is kept close to the chest wall through muscles that pull it against the thoracic wall. (One of these muscles is serratus anterior)

Serratus anterior nerve injury can also cause disability in punching and pushing actions. During the pushing attempts, winging of the scapula becomes very prominent.

Klumpke’s paralysis

This type of paralysis is due to injury to the lower trunk of the brachial plexus. Physical trauma to the arm, such as a sudden pull of the arm to the side, a fall from height, or pulling on a baby’s arm too hard during birth injury can be causes of this paralysis.

The mainly involved nerves in Klumpke’s paralysis are nerves originating from the 8th and first thoracic vertebrae.

Muscles paralyzed in this condition are the hand, forearm, and finger muscles. Kulumke’s paralysis causes a claw-hand appearance due to hyperextension of the hand and finger joints following muscle paralysis.

Other changes that can also occur include:

  • Loss of the skin’s sensory effects
  • Loss of the ability to sweat

The skin with sensory problems is relatively warmer and also drier than the parts of the skin due to sweating loss and sympathetic activity loss. Long-standing Klumpke’s paralysis causes scaliness or dryness of the skin, easy cracking of the finger and nails, and a decrease in the size of the finger pulps.

References
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  4. Johnson EO, Vekris M, Demesticha T, Soucacos PN. Neuroanatomy of the brachial plexus: normal and variant anatomy of its formation. Surgical and radiologic anatomy. 2010 Mar;32(3):291-7.
  5. Fazan VP, Amadeu AD, Caleffi AL, Rodrigues Filho OA. Brachial plexus variations in its formation and main branches. Acta Cirurgica Brasileira. 2003;18:14-8.
  6. Mian A, Chaudhry I, Huang R, Rizk E, Tubbs RS, Loukas M. Brachial plexus anesthesia: a review of the relevant anatomy, complications, and anatomical variations. Clinical Anatomy. 2014 Mar;27(2):210-21.
  7. Brody IA, Wilkins RH. Erb’s palsy. Archives of neurology. 1969 Oct 1;21(4):442-.
  8. Wiater JM, Flatow EL. Long thoracic nerve injury. Clinical orthopaedics and related research. 1999 Nov 1(368):17-27.
  9. Al-Qattan MM, Clarke HM, Curtis CG. Klumpke’s birth palsy: does it really exist?. Journal of hand surgery. 1995 Feb;20(1):19-23.


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