Nerve lying in the spiral groove of humerus is:
**Core Concept**
The spiral groove of the humerus contains a vital nerve that is susceptible to injury during fractures or surgical procedures. This nerve plays a crucial role in the innervation of the arm and forearm.
**Why the Correct Answer is Right**
The radial nerve, a branch of the brachial plexus, traverses the spiral groove of the humerus. This nerve is responsible for innervating the muscles of the posterior arm, forearm, and hand, including the extensor muscles of the wrist and fingers. The radial nerve also provides sensory innervation to the skin of the posterior arm and forearm. As the nerve passes through the spiral groove, it is vulnerable to compression or injury, which can result in radial nerve palsy.
**Why Each Wrong Option is Incorrect**
* **Option A:** The median nerve is not located in the spiral groove of the humerus; it is found in the carpal tunnel at the wrist, where it is susceptible to compression.
* **Option B:** The ulnar nerve is not located in the spiral groove; it passes through the cubital tunnel at the elbow, where it can be compressed.
* **Option C:** The axillary nerve is not located in the spiral groove; it is found in the quadrangular space of the shoulder, where it can be injured during shoulder surgery.
**Clinical Pearl / High-Yield Fact**
The radial nerve is a common site for nerve injury in the arm, often due to compression or trauma. This can result in weakness or paralysis of the extensor muscles of the wrist and fingers, leading to a characteristic "wrist drop" deformity.
**Correct Answer: C. Radial nerve.**