Simple Pharmanotes: Nervous Tissue.

Tissue level of organization: Nervous Tissue.

Introduction:

Groups of cells having similar structure and performing similar functions are called “Tissue.”
Nervous tissue is a highly specialized tissue in the body and is present in the organs of Nervous system.
Nervous tissue is composed of two types of cells;

Neurons: they initiate, receive, conduct and transmit information.
Neuroglial Cells: They provide support to neurons and also perform some important functions.

Neuroglia word is derived from: Nerve Glue.
Four types of neuroglial cells are found in the central nervous system;
Astrocytes: Forms connection between neurons and blood vessels, imp. Part of BBB (Blood Brain Barrier.)
Microglial Cells: Eat microbes and waste, Protection.
Oligodendrocytes: Insulation and synthesis of Myelin Sheath.
Ependymal cells: Helps in circulation of CSF (CerebroSpinal Fluid).

They are the main functional cells of the tissue where information is received, analyzed and stored.
Each nerve cell has following important parts;

Dendrites are cell processes that carry impulses towards the cell, a neuron may have many dendrites.
Cell body is also called “Soma”, contains nucleus and regulates the functioning of neurons.
Axon is a long cell process that carries nerve impulses.
Axon terminals are endings of neurons where neurotransmitters are stored to be released in synapse.
Synapse is a minute space between two neurons, the impulse passes through synapse by means of chemicals called “Neurotransmitters”.
Some neurons containing a sheath of a fatty substance around the axon called ‘Myelin Sheath” are called as “Myelinated Neurons”.
The neurons which are not covered by Myelin sheath are called as ‘Non Myelinated Neurons”
Myelin sheath is covered by a type of glial cell called “Schwann Cell”.
The groove on the Myelinated neuron where myelin sheath is absent and axon is exposed is called the “Node of Ranvier”.
Transfer speed of nerve impulses is faster in myelinated neurons than in unmyelinated neurons.