The Brachial Plexus: An Anatomical Overview

Introduction : Brachial plexus anatomy

The brachial plexus is a group of nerves that arises from the spinal cord in the neck and extends into the arm. These nerves provide the motor and sensory innervation to the arm and hand. In this article we will learn in detail about the anatomy of brachial plexus.

The brachial plexus is made up of four main nerves: the upper and lower trunk, the medial and lateral cord. Each of these nerves is made up of smaller nerves, called roots and branches.

The roots of the brachial plexus arise from the spinal cord between the cervical vertebrae C5-C8. The upper trunk is made up of the C5 and C6 roots, while the lower trunk is made up of the C7 and C8 roots. The medial cord is made up of the C8 and T1 roots, while the lateral cord is made up of the C5-C7 roots.

The branches of the brachial plexus provide innervation to different areas of the arm and hand.

The brachial plexus Anatomy: An overview

BRACHIAL PLEXUS

The anatomy of brachial plexus can be explained as this plexus is the plexus of nerves formed by the anterior (ventral) rami of lower four cervical and the first thoracic (i.e., C5, C6, C7, C8, and T1) spinal nerves with little contribution from C4 to T2 spinal nerves.

N.B. If the contribution from C4 is large and that from T2 is absent, it is called prefixed brachial plexus. On the other hand, if contribution from T2 is large and that from C4 is absent, it is termed postfixed brachial plexus.

Components

The brachial plexus consists of four components: (a) roots, (b) trunks, (c) divisions, and (d) cords. The roots and trunks are located in the neck, divisions behind the clavicle and the cords in the axilla.

Roots

The roots (five) are constituted of anterior primary rami of C5 to T1 spinal nerves. They are located in neck, deep to scalenus anterior muscle.

Trunks

The trunks (three) are formed as follows:

The C5 and C6 roots join to form the upper trunk; the C7 root alone forms the middle trunk and, C8 and T1 roots join to form the lower trunk. They lie in the neck occupying the cleft between scalenus medius behind and the scalenus anterior in front.

Divisions

Each trunk divides into anterior and posterior divisions. They lie behind the clavicle.

Cords

The cords (three) are formed as follows: the anterior divisions of the upper and middle trunks unite to form the lateral cord and the anterior division of the lower trunk continues as the medial cord. The posterior divisions of the three trunks unite to form the posterior cord.

Branches

A. From roots

• Long thoracic nerve/nerve to serratus anterior (C5, C6, and C7).
• Dorsal scapular nerve/nerve to rhomboids (C5). In addition to the long thoracic nerve and dorsal scapular nerve, branches are given by the roots to supply scalene muscles and longus colli (C5, C6, C7, and C8) and there is contribution to phrenic nerve (C5).

B. From trunks

1. Suprascapular nerve (C5 and C6)
2. Nerve to subclavius (C5 and C6)

N.B. The branches arising from roots and trunks are supraclavicular branches of brachial plexus.

C. From cords

1. From lateral cord

• Lateral pectoral nerve (C5, C6, and C7).
• Lateral root of median nerve (C5, C6, and C7).
• Musculocutaneous nerve (C5, C6, and C7).

2. From medial cord

• Medial pectoral nerve (C8 and T1).
• Medial cutaneous nerve of arm (T1).
• Medial cutaneous nerve of forearm (C8 and T1).
• Medial root of median nerve (C8 and T1).
• Ulnar nerve (C7, C8, and T1).

3. From posterior cord

• Radial nerve (C5, C6, C7, C8, and T1).
• Axillary nerve (C5 and C6).
• Thoraco-dorsal nerve/nerve to latissimus dorsi (C6, C7, and C8).
• Upper subscapular nerve (C5 and C6).
• Lower subscapular nerve (C5 and C6).

Applied aspects of Brachial Plexus anatomy

Global total brachial plexus birth baby is the most severe type of paralysis.

1. Erb’s Paralysis

Site of injury: One region of the upper trunk of the brachial plexus is called Erb’s point. Six nerves meet here. Injury to the upper trunk causes Erb’s paralysis.

Causes of injury: Undue separation of the head from the shoulder, which is commonly encountered in the following.

• Birth injury/difficult childbirth
• Fall on the shoulder
• During anaesthesia.

Nerve roots involved: Mainly C5 and partly C6. Muscles paralysed: Mainly biceps brachii, deltoid, brachialis and brachioradialis. Partly supraspinatus, infraspinatus and supinator. Deformity and position of the limb:

• Arm: Hangs by the side; it is adducted andmedially rotated.
• Forearm: Extended and pronated.
• The deformity is known as ‘policeman’s tip hand or waiter’s tip hand or ‘porter’s tip hand’

Disability: The following movements are lost.

• Abduction and lateral rotation of the arm at shoulder joint.
• Flexion and supination of the forearm.
• Biceps and supinator jerks are lost.
• Sensations are lost over a small area over the
• lower part of the deltoid.

2. Klumpke’s Paralysis

Site of injury: Lower trunk of the brachial plexus.

Cause of injury: Undue abduction of the arm, as in clutching something with the hands after a fall from a height, or sometimes in birth injury.

Nerve roots involved: Mainly T1 and partly C8.

Muscles paralysed

• Intrinsic muscles of the hand (T1).
• Ulnar flexors of the wrist and fingers (C8). Deformity and position of the hand: Claw hand due to the unopposed action of the long flexors and extensors of the fingers. In a claw hand, there is hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints.

Disability:

1. Complete claw hand.
2. Cutaneous anaesthesia and analgesia in a narrow zone along the ulnar border of the forearm and hand.
3. Horner’s syndrome: If T1 is injured proximal to white ramus communicans to first thoracic sympathetic ganglion, there is ptosis, miosis, anhydrosis, enophthalmos, and loss of ciliospinal reflex—may be associated. This is because of injury to sympathetic fibres to the head and neck that leave the spinal cord through nerve T1 (Fig. 4.18).
4. Vasomotor changes: The skin area with sensory loss is warmer due to arteriolar dilation. It is also drier due to the absence of sweating as there is loss of sympathetic activity.
5. Trophic changes: Long-standing case of paralysis leads to dry and scaly skin. The nails crack easily with atrophy of the pulp of fingers.

3. Injury to the Nerve to Serratus Anterior (Nerve of Bell)

Causes:

• Sudden pressure on the shoulder from above.
• Carrying heavy loads on the shoulder.

Deformity: Winging of the scapula, i.e. excessive prominence of the medial border of the scapula. Normally, the pull of the muscle keeps the medial border against the thoracic wall.

Disability:

• Loss of pushing and punching actions. During attempts at pushing, there occurs winging of the scapula
• Overhead abduction of shoulder girdle is partly affected due to intact trapezius muscle

To wrap things up

The brachial plexus is a bundle of nerves that extends from the spinal cord to the shoulder. It is responsible for supplying movement and sensation to the arm and hand. This blog post provided a basic overview of the anatomy of the brachial plexus. By understanding this anatomy, we can help reduce the gap between the medical community and the general public.

Do share it among your medical friends and everyone else so that everyone can understand the simple medical terms and help us reach our goal of saving 1,00,000 lives by the end of 2023 through this blog.