Roots of brachial plexus

At a glance

English

Roots of brachial plexus

Latin (TA2)

Radices plexus brachialis

System

Nerve

Region

Neck

Side

Paired, left and right

About the roots of brachial plexus

The roots of the brachial plexus are the anterior rami of the fifth to eighth cervical nerves and the first thoracic nerve. Each ramus has already given its segmental twigs to the deep muscles of the neck before it counts as a plexus root. The roots leave the intervertebral foramina, lie in the gutter of the transverse processes, and emerge between the anterior and middle scalene muscles in the posterior triangle of the neck, close to the subclavian artery.

Above the clavicle the roots combine to make three trunks. C5 and C6 join as the upper trunk, C7 carries on alone as the middle trunk, while C8 joins T1 as the lower trunk, which lies on the first rib behind the subclavian artery. The plexus may be shifted upwards, taking in a branch of C4 (a prefixed plexus), or downwards, taking in T2 (a postfixed plexus).

Three branches leave at root level. The dorsal scapular nerve, mainly from C5, supplies the rhomboids and levator scapulae. The long thoracic nerve, from C5 to C7, supplies serratus anterior, the prime mover in reaching forwards and pushing. A twig from C5 often joins the phrenic nerve. Each root also receives a grey ramus communicans from the sympathetic trunk, bringing sympathetic fibres into the limb nerves; T1 additionally sends a white ramus to the chain.

Root injuries follow predictable patterns. Forceful widening of the angle between neck and shoulder tears the upper roots and leaves the arm hanging rotated inwards (Erb palsy), while violent upward pull of the arm injures C8 and T1 and weakens the small muscles of the hand (Klumpke palsy). An avulsion of T1 near the cord may also interrupt sympathetic fibres to the head and produce Horner syndrome. Paralysis of the rhomboids or of serratus anterior points to damage at or above root level, because their nerves leave so early.

Course and supply

Arises from

Anterior rami of spinal nerves C5 to T1 inclusive, after their segmental branches to the neck muscles.

Ends in

Unite to form the upper, middle and lower trunks of the brachial plexus above the clavicle.

Supplies

Carry all motor and sensory fibres of the upper limb plexus; at root level they give off the dorsal scapular nerve, the long thoracic nerve and a contribution to the phrenic nerve.