Physical Therapy Assistant Practice Exam

What muscle is innervated by the axillary nerve (C5-C6)?

1. Biceps muscle

2. Deltoid muscle

3. Triceps muscle

4. Diaphragm

The correct answer is: Deltoid muscle

The deltoid muscle is innervated by the axillary nerve, which arises from the brachial plexus and specifically contains fibers from the C5 and C6 spinal nerve roots. The deltoid is responsible for shoulder abduction, flexion, and extension, making it a crucial muscle for upper limb movements. The axillary nerve innervates not only the deltoid but also the teres minor muscle, both of which play a role in the overall functionality of the shoulder. Damage to the axillary nerve can lead to weakness in shoulder movements, especially abduction, highlighting the importance of this muscle in daily activities and athletic performance. In comparison, other muscle options listed such as the biceps muscle, which is primarily served by the musculocutaneous nerve, the triceps muscle, innervated by the radial nerve, and the diaphragm, innervated by the phrenic nerve, do not receive innervation from the axillary nerve, making them incorrect choices for this question. Understanding the specific innervation of muscles is vital for physical therapists and assistants, as it aids in diagnosing nerve injuries and devising appropriate rehabilitation strategies.