Brachial Plexus
Direct answer
The brachial plexus is the nerve plexus of the upper limb, formed by the ventral rami of C5, C6, C7, C8 and T1, occasionally with contributions from C4 (prefixed) or T2 (postfixed). It runs from the posterior triangle of the neck into the axilla, organised from proximal to distal into roots, trunks, divisions and cords — "Randy Travis Drinks Cold Beer" gives roots, trunks, divisions, cords, branches. Its five terminal branches are the musculocutaneous, axillary, radial, median and ulnar nerves.
What you must remember
- Roots: C5–T1 ventral rami, emerging between scalenus anterior and scalenus medius in the posterior triangle.
- Trunks: superior (C5–C6), middle (C7) and inferior (C8–T1); each divides behind the clavicle into anterior and posterior divisions.
- Cords: in the axilla, named for their relation to the second part of the axillary artery — lateral, posterior and medial.
- Key branches: from roots — dorsal scapular (C5) and long thoracic (C5–C7, to serratus anterior; injury causes winging of the scapula); from the upper trunk — suprascapular (C5–C6); terminal branches — musculocutaneous (C5–C7), axillary (C5–C6), radial (C5–T1), median (C5–T1, from lateral and medial roots) and ulnar (C8–T1).
- Erb's palsy: upper trunk (C5–C6) injury, classically shoulder dystocia — limb adducted and internally rotated, elbow extended, forearm pronated, wrist flexed: the "waiter's tip" posture.
- Klumpke's paralysis: lower trunk (C8–T1) injury — claw hand from intrinsic muscle paralysis, with Horner syndrome if T1 sympathetic fibres are involved.
- Applied anatomy: interscalene and supraclavicular nerve blocks; thoracic outlet compression can mimic lower trunk lesions.
Common confusion
Students name the cords by their position in the limb instead of by their relation to the second part of the axillary artery, and forget that the median nerve is formed by two roots from two different cords (lateral C5–C7, medial C8–T1). The injuries are also reversed in haste: Erb's is an upper trunk lesion with C5–C6 signs, Klumpke's a lower trunk lesion with C8–T1 signs.
Exam-focused takeaway
In theory, draw the standard diagram with the M-shaped terminal branches around the axillary artery, label the parts with root values, and add one line each on Erb's and Klumpke's palsy. In viva, state the root values first, then the organisation, then a named branch with its clinical test. In practicals and spotters, identify the plexus in the dissected neck and axilla, point out the long thoracic nerve on serratus anterior, and relate the plexus to the interscalene block.
Practise MCQs and previous-year questions on the brachial plexus and nerve injuries in the PrepElephant app. Free notes continue on this website.
Frequently asked questions
What are the root values of the brachial plexus?
The ventral rami of C5 to T1. A contribution from C4 makes it prefixed and from T2 postfixed, but C5–T1 is the expected answer.
What is Erb's palsy?
Upper trunk (C5–C6) paralysis, classically from birth injury, producing adduction and internal rotation of the arm, elbow extension, forearm pronation and wrist flexion — the waiter's tip deformity.
What is Klumpke's paralysis?
Lower trunk (C8–T1) injury causing claw hand from intrinsic muscle paralysis, often with Horner syndrome when T1 sympathetic fibres to the eye are involved.
Why is the long thoracic nerve clinically important?
It supplies serratus anterior (C5–C7); injury causes winging of the scapula — a favourite short answer and viva question.
Which five nerves are the terminal branches?
Musculocutaneous and the lateral root of the median from the lateral cord; axillary and radial from the posterior cord; ulnar and the medial root of the median from the medial cord.
Practise this in the PrepElephant app
Question banks, previous-year questions, mock tests and revision tools — for Brachial Plexus and Anatomy. Free to start.