Biology · Structural Organisation in Animals · NEET
Nissl bodies (Nissl granules) are made of free ribosomes and rough endoplasmic reticulum (RER). They sit in the cell body (cyton) and dendrites of a neuron, but not in the axon, so they help make proteins. The myelin sheath is a fatty cover around the axon made by Schwann cells; the small gaps between two sheaths are called nodes of Ranvier. Memory hook: "Nissl = protein factory in the body, Myelin = fatty jacket on the axon."
A neuron: Nissl bodies (free ribosomes + RER) lie in the cell body and dendrites, never in the axon. The axon is wrapped by a myelin sheath made by Schwann cells, with bare gaps called nodes of Ranvier.
Your doubts, answered
What are Nissl bodies made of?
Nissl bodies (Nissl granules) are made of free ribosomes and rough endoplasmic reticulum (RER). Because ribosomes and RER build proteins, Nissl bodies are the main protein-making sites in a neuron. This exact composition was asked in NEET 2018, so remember: free ribosomes + RER, not DNA or lipids.
Are Nissl bodies present in the axon?
No. Nissl bodies are found in the cell body (cyton) and extend into the dendrites, but they are absent from the axon. This is a very common NEET trap. Easy rule: the axon has no Nissl bodies, so protein synthesis does not happen along the axon itself.
Who makes the myelin sheath?
In the peripheral nervous system (spinal and cranial nerves) the myelin sheath is made by Schwann cells, which wrap around the axon. NCERT names Schwann cells directly. In the central nervous system (brain and spinal cord), the same fatty cover is made by oligodendrocytes. Both are types of neuroglia (supporting cells), not neurons.
What are nodes of Ranvier?
Nodes of Ranvier are the small gaps between two next-door myelin sheaths along a myelinated axon. At these gaps the axon is bare (no myelin). They let the nerve impulse jump from node to node, making conduction faster. Only myelinated fibres have nodes of Ranvier.
What is the difference between myelinated and non-myelinated nerve fibres?
A myelinated nerve fibre is wrapped by Schwann cells that form a myelin sheath around the axon, and it has nodes of Ranvier (found in spinal and cranial nerves). A non-myelinated (unmyelinated) fibre is enclosed by a Schwann cell that does NOT form a myelin sheath, and it has no nodes of Ranvier (found in autonomic and somatic neural systems).
⚠️ The NEET trap ✗ Nissl bodies are found all over the neuron, including the axon. ✓ Nissl bodies are present in the cell body and dendrites but are ABSENT from the axon. 🧠 NEET loves the word 'axon'. If a question says Nissl bodies are in the axon, it is wrong. The axon carries the impulse away and has no Nissl granules, so no protein synthesis happens there.
Real NEET questions
2018
Nissl bodies are mainly composed of
A · Nucleic acids and SER
B · DNA and RNA
C · Proteins and lipids
D · Free ribosomes and RER ✓
Solution: Nissl bodies (Nissl granules) lie in the cyton (cell body) of a neuron and extend into the dendrites, but are absent from the axon. They are made of free ribosomes and rough endoplasmic reticulum (RER) and are the main site of protein synthesis in the neuron. So option D is correct.
2017
Myelin sheath is produced by
A · Schwann Cells and Oligodendrocytes ✓
B · Astrocytes and Schwann Cells
C · Oligodendrocytes and Osteoclasts
D · Osteoclasts and Astrocytes
Solution: The myelin sheath is formed by neuroglial cells. Schwann cells make myelin around axons in the peripheral nervous system, while oligodendrocytes make it in the central nervous system. Astrocytes and osteoclasts (bone cells) do not make myelin, so option A is correct.
Solved Structural Organisation in Animals NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Nissl bodies contain free ribosomes and RER, so their job is protein synthesis in the neuron. These proteins are needed to keep the neuron working and to help it recover after injury.
Is the myelin sheath made of protein or fat?
The myelin sheath is mainly a fatty (lipid) cover. It acts like insulation around the axon and speeds up nerve impulse conduction.
Do all axons have a myelin sheath?
No. Myelinated axons have a myelin sheath (in spinal and cranial nerves), while non-myelinated axons are covered by a Schwann cell without a myelin sheath (in autonomic and somatic systems).
Why is the myelin sheath important for NEET?
NEET frequently asks who makes the myelin sheath (Schwann cells / oligodendrocytes) and about nodes of Ranvier. It is a high-yield, one-line fact from the neural tissue topic.
