All of the following nerves arise from the posterior cord of brachial plexus, EXCEPT:
**Core Concept**
The brachial plexus is a complex network of nerves that arise from the ventral rami of C5 to T1 spinal nerves. It is divided into roots, trunks, divisions, cords, and branches. The posterior cord is one of the three cords that make up the brachial plexus, and it plays a crucial role in innervating the muscles of the upper limb.
**Why the Correct Answer is Right**
The posterior cord is responsible for giving rise to several nerves that supply the muscles of the upper limb. The nerves that arise from the posterior cord include the upper subscapular nerve, lower subscapular nerve, axillary nerve, and radial nerve. These nerves are responsible for innervating the muscles of the scapula, humerus, and forearm, including the deltoid, teres minor, and triceps brachii muscles.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the musculocutaneous nerve arises from the lateral cord, not the posterior cord. The musculocutaneous nerve supplies the biceps brachii, brachialis, and coracobrachialis muscles.
* **Option B:** This option is incorrect because the median nerve arises from the lateral and medial cords, not the posterior cord. The median nerve supplies the muscles of the anterior compartment of the forearm, including the flexor carpi radialis and palmaris longus muscles.
* **Option C:** This option is incorrect because the ulnar nerve arises from the medial cord, not the posterior cord. The ulnar nerve supplies the muscles of the medial compartment of the forearm, including the flexor carpi ulnaris and adductor pollicis muscles.
**Clinical Pearl / High-Yield Fact**
The brachial plexus is a common site for injury, particularly in cases of traumatic shoulder or arm injuries. It is essential to diagnose and manage brachial plexus injuries promptly to prevent long-term functional deficits.
**Correct Answer:** A.