Which nerve is responsible for innervating the deltoid muscle?

The deltoid muscle, which is located on the shoulder, is primarily responsible for the abduction of the arm at the shoulder joint and also contributes to flexion and extension of the arm. The axillary nerve is specifically responsible for innervating the deltoid muscle, stemming from the brachial plexus.

The axillary nerve emerges from the posterior cord of the brachial plexus, generally traveling around the surgical neck of the humerus. This nerve not only supplies motor function to the deltoid but also provides sensory innervation to the skin overlying the shoulder (specifically, the "regimental badge" area).

Understanding the anatomy and function of the axillary nerve is crucial for recognizing the implications of injuries in this region. Damage to the axillary nerve can lead to weakness in shoulder abduction and loss of sensation in the area it supplies, underscoring its role in upper extremity functions.