[2] The radial nerve originates as a terminal branch of the posterior cord of the brachial plexus.
The radial nerve originates from the posterior cord of the brachial plexus with root values of C5 to C8 and T1.
In the arm, it runs behind the brachial artery and then enters the lower triangular space to reach the radial sulcus on the back of the humerus.
After it emerges out from the radial sulcus, it supplies the brachialis, brachioradialis and extensor carpi radialis longus.
[4] It is commonly believed that the radial nerve provides motor innervation to the long head of the triceps.