Nissl bodies, also known as Nissl substance or Nissl granules, are specialized structures found in the cell bodies of neurons. They are named after the German neurologist Franz Nissl, who first described them. These structures play a crucial role in the proper functioning of neurons and are composed of ribosomes and rough endoplasmic reticulum (RER).

Composition of Nissl Bodies:
Nissl bodies are composed of masses of ribosomes and rough endoplasmic reticulum (RER). Ribosomes are small organelles responsible for protein synthesis, while the rough endoplasmic reticulum is involved in the folding and modification of newly synthesized proteins. The presence of these components in Nissl bodies indicates their role in protein production and processing within neurons.

Function of Nissl Bodies:
1. Protein Synthesis: The ribosomes present in Nissl bodies are actively involved in protein synthesis. Neurons require a constant supply of proteins for various cellular processes, including the maintenance and growth of axons and dendrites, signal transmission, and the production of neurotransmitters. Nissl bodies provide the necessary machinery for the efficient synthesis of these proteins.

2. Protein Processing: The rough endoplasmic reticulum (RER) within Nissl bodies helps in the folding and modification of proteins. This includes the addition of sugar molecules (glycosylation) and the formation of disulfide bonds. Proper folding and modification are essential for the functional integrity of proteins, and the RER within Nissl bodies ensures that newly synthesized proteins are correctly processed.

3. Neuronal Function and Plasticity: Nissl bodies are crucial for the normal functioning and plasticity of neurons. They provide the necessary proteins required for the maintenance and growth of neuronal processes, as well as for the production of neurotransmitters and other signaling molecules. Without Nissl bodies, neurons would not be able to carry out their specialized functions effectively.

4. Neurodegenerative Diseases: Changes in Nissl bodies are often observed in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. The accumulation of abnormal proteins, such as tau and alpha-synuclein, can disrupt the normal structure and function of Nissl bodies, leading to neuronal dysfunction and degeneration.

In conclusion, Nissl bodies are specialized structures found in neurons that are composed of ribosomes and rough endoplasmic reticulum. They play a crucial role in protein synthesis, processing, and the normal functioning of neurons. Their disruption can have significant implications for neuronal function and can contribute to neurodegenerative diseases.