The deltoid muscle is innervated by the axillary nerve. The deltoid is a triangular muscle located at the uppermost part of the arm and gives the shoulder its rounded contour. The axillary nerve extends from the brachial plexus, carrying nerve impulses to the deltoid muscle.
The brachial plexus divides into five major nerves as it extends into the arm. The five extensions are the axillary, musculocutaneous, median, radial and ulnar nerves.The axillary nerve stimulates the deltoid and returns information from sensory receptors in this region to the brain. Axillary nerve signals are transmitted through the nerve fibers of spinal nerves C5 and C6.