**Core Concept**
The question is testing the understanding of the distribution and concentration of sodium (Na+) channels in the body, specifically at the cellular and tissue levels. **Sodium channels** are crucial for the transmission of electrical signals in excitable cells, including neurons and cardiac myocytes.

**Why the Correct Answer is Right**
The correct answer is the region with the highest concentration of Na+ channels, which is essential for the initiation and propagation of action potentials. **Voltage-gated sodium channels** are densely packed in the **axon hillock**, the initial segment of the axon, where the action potential is generated. This high concentration of Na+ channels enables the rapid depolarization necessary for neuronal signaling. The axon hillock is the site where the membrane potential reaches threshold, triggering an action potential.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the Na+ channel concentration is not highest in the dendrites, which are primarily involved in receiving synaptic inputs and are not the primary site of action potential generation.
* **Option B:** This option is incorrect because the Na+ channel concentration is not highest in the cell body (soma), which is the site of protein synthesis and other cellular processes, but not the primary site of action potential generation.
* **Option C:** This option is incorrect because the Na+ channel concentration is not highest in the terminal button, which is involved in releasing neurotransmitters, but not the primary site of action potential generation.

**Clinical Pearl / High-Yield Fact**
The **axon hillock** is the most excitable part of the neuron, with a higher concentration of voltage-gated sodium channels, making it the site of action potential initiation. This is a critical concept for understanding the physiology of neuronal signaling.

**Correct Answer:** C. Axon hillock