Nerve
Brachial plexus
Network that redistributes upper-limb nerve fibers
High-yield
C5-C6 form the upper trunk, C7 the middle and C8-T1 the lower. All three posterior divisions join the posterior cord, which ends as the axillary and radial nerves.
Overview
Near the neck and axilla, fibers from several spinal levels join and separate before entering named peripheral nerves. This arrangement lets one nerve carry signals from several spinal segments and lets one segment contribute to several nerves.
Reference facts
- Origin
- Usually the anterior rami of spinal nerves C5-T1; contributions from C4 or T2 can occur
- Root value
- Usual maps: C5 - dorsal scapular; C5-C6 - suprascapular, subclavius, upper/lower subscapular and axillary; C5-C7 - lateral pectoral, musculocutaneous and long thoracic; C6-C8 - thoracodorsal; C8-T1 - medial pectoral, medial arm/forearm cutaneous and ulnar; C5-T1 - radial; median chiefly C6-T1 with variable C5. Segmental maps vary
- Course
- Roots between anterior and middle scalenes; trunks in the lower posterior triangle; divisions behind the clavicle; cords named around the second part of the axillary artery
- Motor
- Most shoulder and upper-limb muscles, including many scapular stabilizers. Trapezius receives its main motor supply through the accessory nerve
- Sensory
- Most upper-limb skin; the shoulder tip also receives C3-C4 supraclavicular nerves, and the axilla/adjacent medial arm receives intercostobrachial supply, usually T2
Mnemonic
Follow the route outward: roots → trunks → divisions → cords → branches. Picture five starting roots, three trunks, six divisions and three cords before the terminal nerves.
Clinical correlation
Upper-plexus injury can weaken shoulder movement and elbow flexion; lower-plexus injury more strongly affects the hand. A nearby sympathetic injury may add Horner syndrome. Real injuries can cross these textbook patterns, so a posture alone cannot identify the damaged level.
Frequently asked questions
What are the roots of the brachial plexus?
Usual maps: C5 - dorsal scapular; C5-C6 - suprascapular, subclavius, upper/lower subscapular and axillary; C5-C7 - lateral pectoral, musculocutaneous and long thoracic; C6-C8 - thoracodorsal; C8-T1 - medial pectoral, medial arm/forearm cutaneous and ulnar; C5-T1 - radial; median chiefly C6-T1 with variable C5. Segmental maps vary.
What muscles does the brachial plexus supply?
Most shoulder and upper-limb muscles, including many scapular stabilizers. Trapezius receives its main motor supply through the accessory nerve.
What is the sensory distribution of the brachial plexus?
Most upper-limb skin; the shoulder tip also receives C3-C4 supraclavicular nerves, and the axilla/adjacent medial arm receives intercostobrachial supply, usually T2.
What is the course of the brachial plexus?
Roots between anterior and middle scalenes; trunks in the lower posterior triangle; divisions behind the clavicle; cords named around the second part of the axillary artery.