A 45-year-old woman is admitted to the hospital with neck pain. An MRI examination reveals a herniated disk in the cervical region. Physical examination reveals weakness in wrist extension and paranesthesia on the back of her arm and forearm. Which of the following spinal nerves is most likely injured?

**Core Concept**
The question requires knowledge of the anatomy and function of the spinal nerves in the cervical region, particularly those responsible for arm and forearm sensation and motor function.

**Why the Correct Answer is Right**
The patient's symptoms of weakness in wrist extension and paresthesia on the back of her arm and forearm suggest an injury to the radial nerve or its corresponding spinal nerve. The radial nerve is a branch of the C5-C8 spinal nerves, but the primary motor and sensory function of the wrist extensors is mediated by the C7 spinal nerve. The C7 spinal nerve is responsible for the motor innervation of the triceps brachii muscle, which extends the forearm at the elbow. The sensory branch of the radial nerve, which provides sensation to the back of the arm and forearm, is also derived from the C7 spinal nerve. Therefore, the most likely injured spinal nerve is the C7 spinal nerve.

**Why Each Wrong Option is Incorrect**
* **Option A:** The C6 spinal nerve primarily innervates the biceps brachii muscle, which flexes the elbow, and the brachialis muscle, which flexes the forearm at the elbow. While the C6 spinal nerve does contribute to the innervation of the arm and forearm, it is not primarily responsible for the symptoms described.
* **Option B:** The C8 spinal nerve primarily innervates the ulnar nerve, which is responsible for sensation on the medial aspect of the arm and forearm, as well as motor function of the intrinsic muscles of the hand. The C8 spinal nerve is less likely to be responsible for the symptoms described.
* **Option D:** The T1 spinal nerve primarily innervates the skin of the medial aspect of the arm and forearm, as well as the serratus anterior muscle. The T1 spinal nerve is not primarily responsible for the symptoms described.

**Clinical Pearl / High-Yield Fact**
The dermatomes of the cervical spinal nerves can be remembered using the mnemonic "C3: shoulder, C4: neck, C5: forearm, C6: arm, C7: middle finger, C8: little finger, T1: medial arm". This can help students quickly identify the spinal nerves responsible for sensation in different areas of the body.

**Correct Answer:** C.