Which of the following muscle is innervated by both musculocutaneous and radial nerve?
**Core Concept**
The question is testing the student's knowledge of the innervation of muscles in the upper limb. Specifically, it is assessing their understanding of the motor innervation of the muscles by the musculocutaneous and radial nerves.
**Why the Correct Answer is Right**
The coracobrachialis and biceps brachii muscles are primarily innervated by the musculocutaneous nerve (C5-C6). However, the biceps brachii also receives a motor branch from the radial nerve (C6-C7), which innervates the short head of the biceps brachii. This unique dual innervation allows for the coordinated contraction of these muscles during elbow flexion and forearm supination.
**Why Each Wrong Option is Incorrect**
* **Option A:** Brachialis muscle is primarily innervated by the musculocutaneous nerve, but it does not receive a significant contribution from the radial nerve.
* **Option B:** Triceps brachii muscle is primarily innervated by the radial nerve, but it does not receive a motor branch from the musculocutaneous nerve.
* **Option D:** Flexor carpi radialis muscle is primarily innervated by the median nerve, but it does not receive a motor branch from either the musculocutaneous or radial nerve.
**Clinical Pearl / High-Yield Fact**
The biceps brachii muscle is a classic example of a muscle with dual innervation, which can sometimes lead to confusion during clinical examination or surgical procedures. Familiarity with this unique anatomical arrangement is essential for accurate diagnosis and treatment.
**Correct Answer: C. Biceps brachii.**