Which nerve innervates the deltoid muscle?

The deltoid muscle, which is primarily responsible for shoulder abduction, flexion, and extension, is innervated by the axillary nerve. This nerve arises from the posterior cord of the brachial plexus and specifically provides motor innervation to the deltoid muscle.

In addition to its role in shoulder movement, the axillary nerve also innervates the teres minor muscle and provides sensory innervation to the skin overlying the deltoid muscle. This anatomical relationship is critical for understanding shoulder function and the potential impacts of nerve injury in that region, such as loss of shoulder abduction.

The other nerves listed do not serve this function. The median nerve primarily innervates the flexor muscles of the forearm and some intrinsic hand muscles, the musculocutaneous nerve primarily innervates the anterior compartment of the arm, and the radial nerve mainly innervates the posterior compartment of the arm and forearm muscles. Thus, the axillary nerve is specifically responsible for both motor and sensory functions related to the deltoid muscle.