Final answer:
The lower subscapular nerve is innervated by spinal nerves C5 and C6, which are part of the brachial plexus. It provides motor innervation to muscles such as the subscapularis and teres major that are involved in shoulder movements.
Step-by-step explanation:
The lower subscapular nerve is a branch of the brachial plexus, specifically innervated by the C5 and C6 spinal nerves. The brachial plexus is associated with the lower cervical spinal nerves and the first thoracic spinal nerve, comprising spinal nerves C4 through T1, which reorganize to give rise to the nerves of the arms. This plexus includes nerves like the axillary, radial, ulnar, and median nerves.
The lower subscapular nerve supplies motor innervation to the subscapularis and teres major muscles, which play roles in the movement of the shoulder joint. Given that C5 and C6 are involved in the formation of this nerve, it aligns with the general organization of the spinal nerves and their corresponding muscles and functions in the upper limb.