Question

Nissl granules are absent in
a. Axon
b. Dendron
c. Soma
d. All of the above

Answer 1

Hint: Neurons are the working unit of the brain; it helps in transmitting information from one nerve cell to another. They are the cells present in the nervous system. The morphological structure of neurons includes dendrites, soma, and axons.

Complete answer:
A large granular body found in neurons is called a neuron. These granules are of the rough ER and are the site of protein synthesis. They help in protein synthesis in neurons and the proteins are used in intracellular mechanisms.

- Nissl's granules are the granular structure that is present in the neurons.
- Nissl bodies are nodal points in the endoplasmic reticulum, which permeate the cell body and dendrites.
- The function of nissl granules includes the manufacture and release of proteins and amino acids.
- It is localized in the cyton and dendron and visualized by the Nissl staining method which has an affinity for basic dyes. Nissl granules are present in the cytoplasm of the cell body of the neurons along with other cell organelles like the Golgi apparatus, endoplasmic reticulum, mitochondria, nucleus. These granules give a slight color appearance to the cytoplasm of the cell body.
- The proteins produced by it are used for inter-cellular mechanisms.
- An axon is the tubular process of the nerve cell, that carries impulses away from the cell body. It arises from the cyton at the axon hillock. It has only neurofibrils. Here Nissl's granules are absent.
- Axon cannot synthesize its protein hence it depends on soma.
- The hillock is a region where materials are committed to the axon (cytoskeletal elements, mitochondria) or are excluded from the axon (RER).
- The quantity of Nissl material in the cell is roughly proportional to the size of the cell, but both this and the arrangement of the granules vary in different states of physiological activity.
- The Soma also called a cell body of a neuron contains the nucleus and other structures common to living cells.
- Small nerve cells of the central nervous system sometimes contain no Nissl bodies.
- So, Nissl granules are absent in the axon.

Hence, the correct answer is option (A).

Note: Dendrites are branched protoplasmic extensions of a nerve cell that helps in the propagation of the electrochemical stimulation to the cell body, or soma. They contain numerous, smooth endoplasmic reticulum, Golgi apparatus, and cytoskeletal structures. These structures support the chemical processing of the neuron that is the production of neurotransmitters.