Neurons (Nerve cells)
Structural and functional units of neural tissue are called neurons. A neuron is differentiated into two parts: cyton and neurites.
- Cyton (Cell body, Soma, Perikaryon): The cyton contains cytoplasm (neuroplasm), nucleus mitochondria, Golgi bodies, rough endoplasmic reticulum, ribosomes, lysosomes, fat globules, etc. Besides these, the presence of Nissl granules and neurofibrils is characteristic of all neurons. Nissl granules are irregular masses of ribosomes and rough endoplasmic reticulum. They probably synthesize proteins in the cell. Neurons lack a centrosome.
- Neurites: The processes of neurons are called neurites. The latter are of two types: dendrons or dendrites and an axon or axis cylinder. The part of cyton from where the axon arises is called the axon hillock. The axon ends in a group of branches, the terminal arborizations (axon endings). Certain axons also give rise to side branches, called collateral fibers. The neuroplasm of the axon contains abundant neurofibrils and mitochondria, but Nissl granules, Golgi bodies, ribosomes, and fat globules are absent.
Synapse
The region of the union of the terminal arborization of the axon of one neuron with the dendrites of another neuron is called a synapse. Impulses are transferred from one neuron to the next neuron through synapses.
Neural Tissue
All living organisms are made of cells. A unicellular organism has a single cell in its body, i.e., a single cell performs all basic life activities. However, in multicellular organisms, there are millions of cells. Most of these cells are specialized to carry out only a few functions efficiently. These functions are taken up by a distinct group of cells. Thus, it can be said that there is a division of labor in multicellular organisms.
A tissue is a group of cells that are similar in structure, origin, and function. The term ’tissue’ was given by Bichat. The branch of science dealing with the tissues is called ‘histology’. Mayer introduced the term histology. Malpighi is considered the “founder of histology. Broadly animal tissues are classified into four types: epithelial, connective, muscular, and neural.
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