Injury occurs at C7 root, in what pa of arm, sensation will be lost
**Core Concept**
The C7 nerve root originates from the cervical spine and contributes to the formation of the brachial plexus, a complex network of nerves that innervates the upper limb. The brachial plexus is responsible for transmitting sensory information from the arm to the spinal cord.
**Why the Correct Answer is Right**
The C7 nerve root primarily contributes to the formation of the posterior cord of the brachial plexus. The posterior cord gives rise to the axillary nerve and the radial nerve. The radial nerve is responsible for the sensation of the back of the arm, specifically the area between the lateral epicondyle of the humerus and the posterior aspect of the arm. Therefore, an injury to the C7 nerve root would result in the loss of sensation in this specific area.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the C7 nerve root does not primarily contribute to the formation of the musculocutaneous nerve, which is responsible for the sensation of the lateral aspect of the forearm.
* **Option B:** This option is incorrect because the C7 nerve root does not primarily contribute to the formation of the median nerve, which is responsible for the sensation of the palmar aspect of the thumb, index, middle finger, and part of the ring finger.
* **Option C:** This option is incorrect because the C7 nerve root does not primarily contribute to the formation of the ulnar nerve, which is responsible for the sensation of the little finger and part of the ring finger.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the brachial plexus is a complex network of nerves that can be affected by various insults, including trauma, compression, and tumors. A thorough understanding of the anatomy and function of the brachial plexus is crucial for diagnosing and managing upper limb disorders.
**Correct Answer: D. The back of the arm between the lateral epicondyle of the humerus and the posterior aspect of the arm.**