**Core Concept**
Nissl bodies, also known as Nissl granules or ribosomal clusters, are specialized structures found in the cell body (soma) of neurons. They are responsible for protein synthesis, which is essential for neuronal function, growth, and maintenance.

**Why the Correct Answer is Right**
Nissl bodies contain ribosomal RNA (rRNA) and are the site of protein synthesis in neurons. They are composed of rough endoplasmic reticulum (RER) and ribosomes, which are responsible for translating messenger RNA (mRNA) into proteins. This process is crucial for the production of neurotransmitters, enzymes, and structural proteins necessary for neuronal function. The presence of Nissl bodies in the cell body of neurons allows for efficient protein synthesis and transport to other parts of the neuron.

**Why Each Wrong Option is Incorrect**
**Option B:** Dendrites are branching extensions of the neuron that receive synaptic inputs from other neurons. While they do contain some organelles, they are not primarily involved in protein synthesis.
**Option C:** The axon is the long, thin extension of the neuron that conducts electrical signals away from the cell body. It does not contain Nissl bodies and is not responsible for protein synthesis.
**Option D:** This option is incorrect because only the cell body of neurons contains Nissl bodies, not all parts of the neuron.

**Clinical Pearl / High-Yield Fact**
The presence of Nissl bodies in the cell body of neurons is a characteristic feature that distinguishes neurons from other types of cells. This can be useful in identifying neurons in histological sections.

**Correct Answer:**
✓ Correct Answer: A. Nissl bodies