A 45-year-old man is admitted to the hospital after a car crash. Radiographic examination reveals mild disk herniations of C7, C8, and T1. The patient presents with a sensory deficit of the C8 and T1 spinal nerve dermatomes. The dorsal root ganglia of C8 and T1 would contain cell bodies of sensory fibers carried by which of the following nerves?

**Core Concept**
The dorsal root ganglia (DRG) is a cluster of neuron cell bodies located within the dorsal roots of the spinal cord. These ganglia contain the cell bodies of sensory neurons that transmit information from the periphery to the central nervous system. The specific nerve that carries sensory fibers through the DRG is determined by the spinal nerve segment that corresponds to the dermatome affected.

**Why the Correct Answer is Right**
The patient presents with sensory deficit of the C8 and T1 spinal nerve dermatomes, indicating that the sensory fibers transmitted through the DRG of C8 and T1 are involved. The dorsal root ganglia of C8 and T1 would contain the cell bodies of sensory fibers carried by the posterior roots of the corresponding spinal nerves. Since the posterior roots of C8 and T1 spinal nerves merge to form the posterior root of the brachial plexus, the correct answer is the nerve that forms the posterior root of the brachial plexus.

**Why Each Wrong Option is Incorrect**
**Option A:** The superior trunk of the brachial plexus is formed by the C5 and C6 spinal nerves, which do not correspond to the C8 and T1 dermatomes affected in this patient. **Option B:** The middle trunk of the brachial plexus is formed by the C7 spinal nerve, which is partially involved but not the primary nerve responsible for the C8 and T1 dermatomes. **Option D:** The inferior trunk of the brachial plexus is formed by the C8 and T1 spinal nerves, which corresponds to the affected dermatomes.

**Clinical Pearl / High-Yield Fact**
The dorsal root ganglia are responsible for transmitting sensory information from the periphery to the central nervous system, and damage to these ganglia can result in sensory deficits. Understanding the anatomy of the dorsal root ganglia and the nerves that correspond to specific spinal nerve segments is crucial for diagnosing and managing neurological disorders.

**Correct Answer:** C.

✓ Correct Answer: A. Medial antebrachial cutaneous nerve