In the nervous system, Nissl granules (Nissl bodies) are characteristic basophilic structures found in the cytoplasm of which type of cell?

Introduction:
Nissl granules, also called Nissl bodies, are important microscopic features used to identify certain cell types in the nervous system. They appear as darkly staining clumps in the cell body when viewed under a light microscope with appropriate stains. This question checks whether you can correctly identify the type of cell in which Nissl granules are found and distinguish it from other cells like eosinophils, glial cells and lymphocytes.

Given Data / Assumptions:
- The structure in question is Nissl granules or Nissl bodies. - Options include eosinophil, glial cell, neuron and lymphocyte. - We assume standard histology definitions and staining characteristics. - The question concerns the typical site where these granules are seen under a microscope.

Concept / Approach:
Nissl granules are aggregations of rough endoplasmic reticulum and ribosomes that stain intensely with basic dyes because of their high RNA content. They are characteristic of the soma (cell body) and dendrites of neurons, where they are involved in protein synthesis needed for neuronal function and maintenance. Eosinophils are white blood cells with large eosinophilic granules, glial cells support neurons but do not show prominent Nissl bodies and lymphocytes are small white blood cells with dense nuclei and scant cytoplasm. Therefore, neurons are the cell type where Nissl granules are a prominent identifying feature.

Step-by-Step Solution:
Step 1: Recall that neurons have a large cell body (soma) that contains organelles needed for high metabolic and synthetic activity. Step 2: Recognise that rough endoplasmic reticulum and ribosomes cluster together as Nissl bodies, especially in the soma and proximal dendrites. Step 3: Understand that these bodies are stained with basic dyes such as cresyl violet and appear as dark granular material. Step 4: Contrast this with eosinophils, which show bright pink cytoplasmic granules due to eosin staining but are not called Nissl granules. Step 5: Note that glial cells have different cytoplasmic features and do not show the classic Nissl pattern. Step 6: Recognise that lymphocytes are mostly nucleus with very little cytoplasm, so they also lack visible Nissl bodies. Step 7: Conclude that neurons are the only correct option where Nissl granules are a characteristic structure.

Verification / Alternative check:
Neurohistology textbooks regularly describe Nissl bodies as a hallmark of neuron cell bodies and emphasise that they disappear or dissolve during certain injuries, a process called chromatolysis. Micrographs show these granules in large multipolar neurons in the spinal cord and brain. Descriptions of eosinophils, lymphocytes and glial cells focus on different staining properties and organelles. No authoritative source claims that Nissl granules are found in these other cells, confirming that neurons are the correct answer.

Why Other Options Are Wrong:
Eosinophil: A granulocytic white blood cell with large eosinophilic granules, not Nissl bodies; its granules contain enzymes related to allergic and parasitic responses. Glial cell: Support cells in the nervous system such as astrocytes and oligodendrocytes; they do not display prominent Nissl bodies like neurons. Lymphocyte: A type of white blood cell with a round, dense nucleus and thin rim of cytoplasm; it lacks the extensive rough endoplasmic reticulum that forms Nissl granules.

Common Pitfalls:
Students sometimes confuse eosinophilic granules with Nissl granules because both names include the word granules and both involve staining. Another mistake is to assume that all nerve related cells, including glial cells, must have Nissl bodies. To avoid confusion, remember that Nissl granules are associated with rough endoplasmic reticulum for protein synthesis, which is especially prominent in the large cell body of neurons, not in small or supportive cells.

Final Answer:
Nissl granules are characteristic cytoplasmic structures found in the cell bodies and dendrites of Neurons.