Concept: This question tests your knowledge of the composition and function of specific neuronal structures, particularly Nissl's bodies.

Why (B) is correct: Nissl's bodies (also known as Nissl granules or tigroid bodies) are characteristic granular structures found in the cytoplasm of neurons, especially in the cell body (soma) and dendrites. They are primarily composed of aggregates of rough endoplasmic reticulum (RER) and free ribosomes. These structures are crucial for the synthesis of proteins, particularly those needed for neuronal growth and regeneration, and neurotransmitter production.

Why other options are wrong:

• (A) proteins and lipids: While Nissl's bodies contain proteins (ribosomal proteins, RER proteins) and some lipids (from RER membranes), this is not their primary or most defining composition.
• (C) nucleic acids and SER: Nissl's bodies contain RNA (ribosomal RNA, mRNA) but not primarily SER. SER is involved in lipid synthesis and detoxification, not protein synthesis in this context.
• (D) DNA and RNA: Nissl's bodies contain RNA, but DNA is primarily found in the nucleus.

Common Mistake: Students might confuse Nissl's bodies with other cellular inclusions or organelles. Remember their specific role in protein synthesis within neurons.

NEET Tip: Think of Nissl's bodies as the "protein factories" of the neuron. Their presence indicates high metabolic activity and protein synthesis.

Correct Answer: (B)