Physical Therapy Assistant Practice Exam

Which muscle is innervated by the radial nerve (C7-C8)?

1. Biceps muscle

2. Deltoid muscle

3. Triceps muscle

4. Phrenic muscle

The correct answer is: Triceps muscle

The triceps muscle is innervated by the radial nerve, which arises from the brachial plexus and primarily carries contributions from the C7 and C8 spinal cord segments. The triceps muscle plays a crucial role in extending the elbow joint, and proper functioning of this muscle is essential for a variety of daily activities and movements. The radial nerve innervates the triceps at the posterior aspect of the arm, allowing for the extension of the forearm at the elbow. This contrasts with other muscles mentioned in the choices. For example, the biceps muscle is primarily innervated by the musculocutaneous nerve, while the deltoid muscle is innervated by the axillary nerve. Additionally, the phrenic muscle, which is critical for diaphragm function and thus respiration, is innervated by the phrenic nerve and is not associated with the upper limb musculature. The specificity of the radial nerve's innervation to the triceps explains why it is the correct choice.