Question

Nissl's granules are found in all except (a) Cyton (b) Dendrites (c) Axon (d) Cell body

Short answer

The correct answer is (c) Axon.

Step-by-step solution

Understand the Concept

Knowing what Nissl's granules or bodies are and their function in a neuron plays a key role in this exercise. Nissl's bodies are found in neurons and are made up of rough endoplasmic reticulum with rosettes of free ribosomes, making them the site of protein synthesis.

Remember Their Location

Nissl's bodies are located in the cytoplasm of neurons, specifically in the dendrites and cell body (cyton). Since protein synthesis occurs here, it excludes areas of the neuron where protein synthesis doesn't typically happen.

Identify the Exception

The only location amongst the options provided where Nissl's bodies would not be found is in the axon of the neuron.

Key concepts

Neuron Structure

Neurons are the fundamental units of the brain and nervous system, responsible for carrying out all the essential functions of the nervous system. Understanding their structure is crucial to grasp how they operate in such a complex system. A typical neuron comprises three main parts: the cell body (also known as the soma or cyton), dendrites, and axon.

The cell body contains the nucleus and is the metabolic center of the neuron. It is crucial for maintaining the neuron’s health and functioning. Dendrites branch out from the cell body and act like antennas to receive signals from other neurons. The axon, on the other hand, is a long, thin structure that carries impulses away from the cell body to other neurons or muscles, enabling communication throughout the body.

These key components work together seamlessly to process and transmit information through electrical and chemical signals.

Protein Synthesis

Protein synthesis is a fundamental process that occurs in all living cells, including neurons. It involves the production of proteins, which are essential for a wide range of cellular functions, from structural roles to enzyme catalysis. In neurons, proteins play crucial roles in maintaining cell shape, producing neurotransmitters, and regulating the transmission of signals.

Within the cell body of neurons, protein synthesis is carried out by structures called ribosomes. These ribosomes can be found either floating freely in the cytoplasm or attached to the rough endoplasmic reticulum (RER), forming Nissl bodies.

Two main processes are involved in protein synthesis: transcription and translation. Transcription occurs in the nucleus, where DNA is used to create messenger RNA (mRNA). Translation occurs when mRNA is used by ribosomes to build proteins. Neurons have a high demand for protein synthesis, particularly in the cell body and dendrites, to maintain their structural and functional integrity.

Nissl Granules Location

Nissl granules, also known as Nissl bodies, are critical for understanding where protein synthesis occurs within a neuron. These granules are composed of rough endoplasmic reticulum with rosettes of ribosomes, providing the machinery necessary for the creation of proteins.

They are located predominantly in the cell body (cyton) and dendrites, where a significant amount of protein synthesis is needed to support various neuronal functions.

• The cell body is rich in Nissl bodies because it is the metabolic hub of the neuron, requiring substantial protein production to support cell maintenance and signal processing activities.
• Dendrites have Nissl granules as well because they require proteins to manage the reception and processing of neural signals.

However, Nissl granules are noticeably absent from the axon. The axon is primarily involved in transmitting signals over long distances rather than synthesizing proteins, which explains the absence of these protein synthesis centers in this part of the neuron.