Physical Therapy Assistant Practice Exam

Which muscle is innervated by the musculocutaneous nerve (C5-C6)?

1. Biceps muscle

2. Deltoid muscle

3. Triceps muscle

4. Diaphragm

The correct answer is: Biceps muscle

The biceps muscle is innervated by the musculocutaneous nerve, which originates from the C5 and C6 spinal nerve roots. This nerve primarily targets muscles in the anterior compartment of the arm, with the biceps brachii being a major muscle involved in elbow flexion and forearm supination. The musculocutaneous nerve provides motor innervation to other muscles in this compartment, including the brachialis and coracobrachialis, but the biceps muscle is often the most recognized due to its prominent function and anatomical location. In contrast, the deltoid muscle is primarily innervated by the axillary nerve, which does not originate from the C5-C6 roots, but rather from the posterior cord of the brachial plexus. The triceps muscle is innervated by the radial nerve, which is responsible for extending the elbow. The diaphragm, a major muscle for respiration, is innervated by the phrenic nerve, which arises from the cervical nerves C3-C5, highlighting the distinct pathways and innervations of these muscles separate from those supplied by the musculocutaneous nerve.