Radial Nerve — Origin, Root Value and Relations in the Axilla
Origin
The radial nerve is the largest branch of the posterior cord of the brachial plexus.
It is also called the musculospiral nerve (because of its spiral course in the radial groove of the humerus).
Root Value
C5, C6, C7, C8, T1
The dominant root values are C7 and C8. It carries fibres from all five roots of the brachial plexus.
Origin Point
Given off from the posterior cord in the lower part of the axilla, at the lower border of the pectoralis minor.
Relations in the Axilla
The radial nerve passes posterior to the third part of the axillary artery.
| Direction | Relation |
|---|---|
| Anteriorly | Third part of the axillary artery |
| Posteriorly | Subscapularis, latissimus dorsi, teres major |
| Laterally | Axillary nerve, coracobrachialis |
| Medially | Axillary vein |
Exit from the Axilla
The radial nerve leaves the axilla by passing through the lower triangular space (quadrilateral space is for axillary nerve; lower triangular space is bounded by teres major above, long head of triceps medially, and humerus laterally).
It enters the posterior compartment of the arm accompanied by the profunda brachii artery.
Branch Given in the Axilla
- Posterior cutaneous nerve of the arm — supplies skin on the back of the arm (posterior surface of arm down to the olecranon)
- Muscular branches to the long head and medial head of triceps brachii