Which nerve innervates the deltoid muscle?

The deltoid muscle is primarily innervated by the axillary nerve. This nerve emerges from the posterior cord of the brachial plexus and specifically serves the deltoid muscle as well as the teres minor muscle. The axillary nerve provides the necessary motor function for shoulder abduction, flexion, and extension, all of which are key actions performed by the deltoid.

Understanding the role of the axillary nerve is crucial in diagnosing and treating shoulder-related injuries and conditions, since damage to this nerve can lead to weakness in shoulder movements and sensory loss in the region over the lateral shoulder. The axillary nerve's relationship with the shoulder joint also highlights its important role in maintaining shoulder stability and function.