A penetrating wound to the axilla which severs the posterior cord of the brachial plexus would denervate the?
**Core Concept**
The brachial plexus is a complex network of nerves that originates in the spinal cord and controls muscle movements and sensation in the shoulder, elbow, wrist, and hand. The **posterior cord** of the brachial plexus is formed by the union of the posterior divisions of the three trunks. It gives rise to the **axillary nerve** and the **radial nerve**.
**Why the Correct Answer is Right**
A penetrating wound to the axilla that severs the **posterior cord** of the brachial plexus would denervate the muscles supplied by the **axillary** and **radial nerves**. The **radial nerve** is responsible for extension of the wrist and fingers, and the **axillary nerve** supplies the deltoid and teres minor muscles, which are involved in shoulder abduction and adduction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the posterior cord primarily gives rise to nerves that supply the posterior aspect of the arm.
**Option B:** This option is incorrect because the musculocutaneous nerve, which supplies the biceps brachii, arises from the lateral cord.
**Option C:** This option is incorrect because the median nerve, which supplies muscles involved in wrist and finger flexion, arises from both the lateral and medial cords.
**Clinical Pearl / High-Yield Fact**
The **radial nerve** is particularly susceptible to injury due to its proximity to the humerus, and its dysfunction can lead to **wrist drop**, a condition characterized by the inability to extend the wrist.
**Correct Answer:** D. muscles of the posterior arm, including those involved in wrist and finger extension, and the deltoid and teres minor muscles.