CorpusHuman Anatomy
NervousPlexus

Brachial plexus

Plexus brachialis

Also known as: C5–T1 plexus, roots trunks divisions cords branches

The network formed by the ventral rami of C5–T1 that supplies the whole upper limb. It is organised from medial to lateral into roots, trunks, divisions, cords and terminal branches, running from the neck through the cervicoaxillary canal into the axilla.

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Overview

RootsC5–T1 ventral rami
Components5 roots, 3 trunks, 6 divisions, 3 cords, 5 terminal branches
Cords named relative to2nd part of axillary artery
Largest branchRadial nerve

The brachial plexus begins as the five roots (ventral rami of C5–T1), which emerge between the anterior and middle scalene muscles together with the subclavian artery. Variants are common: a "prefixed" plexus takes C4 and a "postfixed" plexus takes T2. The roots unite into three trunks in the posterior triangle of the neck:
• superior (C5–C6);
• middle (C7);
• inferior (C8–T1), which lies on the first rib behind the subclavian artery.

Behind the clavicle, each trunk splits into an anterior division, which supplies flexor compartments, and a posterior division, which supplies extensor compartments. In the axilla the divisions regroup into three cords, named by their position relative to the second part of the axillary artery:
• lateral cord: anterior divisions of the superior and middle trunks (C5–C7);
• medial cord: anterior division of the inferior trunk (C8–T1);
• posterior cord: all three posterior divisions (C5–T1).

The cords end in five terminal branches around the third part of the axillary artery: musculocutaneous, axillary, radial, median and ulnar. The lateral and medial roots of the median nerve form a characteristic "M" in front of the artery, together with the musculocutaneous and ulnar nerves, which is a dissection landmark. The supraclavicular part (roots and trunks) is accessible for interscalene and supraclavicular nerve blocks. The infraclavicular part (cords and branches) lies within the axillary sheath.

Location

From the posterior triangle of the neck (between the anterior and middle scalenes), behind the clavicle (cervicoaxillary canal), into the axilla, around the axillary artery.

Parts & subdivisions

  1. Roots (C5–T1)
    Five ventral rami emerging between the anterior and middle scalenes. Branches: dorsal scapular (C5) and long thoracic (C5–C7). A lesion here, proximal to the dorsal root ganglion (root avulsion), may also give Horner syndrome (T1) and paralysis of serratus anterior or the rhomboids.
  2. Trunks
    - Superior: C5 + C6. It gives the suprascapular nerve and the nerve to subclavius. • Middle: C7 alone. • Inferior: C8 + T1, lying on the first rib. It is vulnerable to a cervical rib or a Pancoast tumour.
  3. Divisions
    Each trunk divides behind the clavicle into anterior (flexor) and posterior (extensor) divisions. No named branches arise from the divisions.
  4. Cords
    Named by their relation to the second part of the axillary artery, behind pectoralis minor: • Lateral cord (C5–C7). • Medial cord (C8–T1); it crosses behind the artery to reach its medial side. • Posterior cord (C5–T1).
  5. Terminal branches (MARMU)
    - Musculocutaneous (C5–C7) • Axillary (C5–C6) • Radial (C5–T1) • Median (C5/6–T1) • Ulnar (C8–T1, ± C7)

Anatomy

Innervation

All the muscles and skin of the upper limb, except trapezius (CN XI), the skin over the shoulder tip (supraclavicular nerves, C3–C4) and the upper medial arm (intercostobrachial nerve, T2). It also supplies the shoulder girdle muscles, including the rhomboids, serratus anterior, the pectorals and latissimus dorsi.

Nerve roots

Ventral rami of C5, C6, C7, C8 and T1 (with possible contributions from C4 or T2).

Branches

From the roots:
• Dorsal scapular (C5): rhomboids and levator scapulae.
• Long thoracic (C5–C7): serratus anterior.
• A contribution to the phrenic nerve (C5).

From the superior trunk:
• Suprascapular (C5–C6): supraspinatus and infraspinatus.
• Nerve to subclavius (C5–C6).

From the lateral cord:
• Lateral pectoral (C5–C7).
• Musculocutaneous (C5–C7).
• Lateral root of the median nerve.

From the medial cord:
• Medial pectoral (C8–T1).
• Medial cutaneous nerve of the arm (T1).
• Medial cutaneous nerve of the forearm (C8–T1).
• Ulnar (C7–T1).
• Medial root of the median nerve.

From the posterior cord:
• Upper subscapular (C5–C6).
• Thoracodorsal (C6–C8): latissimus dorsi.
• Lower subscapular (C5–C6): subscapularis and teres major.
• Axillary (C5–C6).
• Radial (C5–T1).

Relations

- The roots and trunks lie between the anterior and middle scalenes with the subclavian artery (the subclavian vein passes in front of the anterior scalene).
• The inferior trunk lies on the first rib.
• The divisions pass behind the clavicle and subclavius.
• The cords surround the second part of the axillary artery deep to pectoralis minor, within the axillary sheath.

Function

  • Motor supply to all muscles of the upper limb and most of the shoulder girdle
  • Cutaneous sensation of almost the whole upper limb
  • Proprioception from the joints and muscles of the upper limb
  • Sympathetic postganglionic fibres (via grey rami) to the vessels and sweat glands of the upper limb

Clinical significance

Erb–Duchenne palsy (upper trunk, C5–C6)

Caused by forceful widening of the angle between the neck and shoulder, for example a fall on the shoulder, a motorcycle accident or shoulder dystocia at birth. The limb takes up the "waiter's tip" posture:
• adducted, from loss of deltoid and supraspinatus;
• medially rotated, from loss of infraspinatus and teres minor;
• elbow extended, from loss of biceps and brachialis;
• forearm pronated, from loss of biceps and supinator;
• the wrist is often flexed.

There is sensory loss over the lateral arm and forearm, and the biceps reflex is lost.

Klumpke palsy (lower trunk, C8–T1)

Caused by hyperabduction of the arm, such as grabbing a branch to break a fall or a breech delivery with the arm overhead. It also occurs with a cervical rib or a Pancoast tumour. It paralyses all the intrinsic muscles of the hand, producing a claw hand (MCP hyperextension with IP flexion of all the fingers), and causes sensory loss along the medial forearm and hand. If the T1 root is avulsed proximal to the white ramus communicans, there is an ipsilateral Horner syndrome.

Brachial plexus blocks

Interscalene, supraclavicular, infraclavicular and axillary approaches give regional anaesthesia of the upper limb. The interscalene block, used for shoulder surgery, spares the lower trunk (C8–T1, the ulnar territory) and almost always blocks the phrenic nerve. The supraclavicular block carries a risk of pneumothorax.

Mnemonics

Organisation

"Randy Travis Drinks Cold Beer": Roots, Trunks, Divisions, Cords, Branches.

Terminal branches

"MARMU", from lateral to medial: Musculocutaneous, Axillary, Radial, Median, Ulnar.

Posterior cord branches

"STAR": Subscapulars (upper and lower), Thoracodorsal, Axillary, Radial.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.