Nervous Tissue

Nervous tissue stimulates muscle contraction, raises environmental awareness, and is involved in emotions, memory, and reasoning. To do all of this, nerve tissue cells must be able to communicate with one another via electrical nerve impulses. The cell body is the most important part of the cell, the part that performs all of the functions. Dendrites are cytoplasmic outgrowths or processes that carry impulses to the cell body. An neuron is a type of extension or process that carries impulses away from the cell body.

Nervous tissue also consists of cells that support the implementation of the neurons rather than transmitting impulses. The glial cells (neuroglial cells) are known collectively as the neuroglia. Supporting cells, also known as glia, bind and insulate neurons. Others provide nutrients by binding blood vessels to the neurons, while some are phagocytic and protect against bacterial invasion.

Definition 

Nervous tissue:- The nerve tissue, also known as nervous tissue, is the main tissue of our nervous system. It keeps track of and regulates the body’s functions. Nervous tissue is made up of two types of cells: nerve cells, also known as neurons, and glial cells, which aid in the transmission of nerve impulses as well as providing nutrients to neurons. Nervous tissue makes up the brain, spinal cord, and nerves, which are specialised for being stimulated to transmit stimulus from one part of the body to another quickly.

Structure of nervous tissue 

• It is mainly composed of nerve cells or neurons, each of which has an axon attached to it. Axons are long stem-like extensions that emerge from the cell and are responsible for communicating with other cells known as Target cells, allowing impulses to be passed.
• The cell body, which includes the nucleus, cytoplasm, and cell organelles, is the most important part. The term “process” refers to the extension of the cell membrane.
• The dendrite is a branching process that obtains information from other neurons and synapses (specialized point of contact). Dendrites connect with the cell body and provide information from other neurons.
• As information passes through neurons from dendrites to cell body and down the axon, it is unidirectional.

Properties of nervous tissue 

Excitability and conductivity are two remarkable characteristics of nervous tissue.

(i)Excitability: Excitability refers to the ability of nerve cells and fibres to respond to a stimulus by entering an active state known as excitation. Excitation occurs at the receptors as a result of various stimuli that constantly act on the organisms, such as light, temperature, chemical, electrical, or pressure.

(ii) Conductivity: The excitation does not stay where it started. It travels through nerve fibres. Conductivity is the ability to transmit excitation in a specific direction. 

Functions of nervous tissue 

• Nerve impulses are generated and carried out by neurons. They do this by secreting chemical neurotransmitters, which produce electrical signals that can be transmitted over long distances.
•  It reacts to stimuli.
• It organizes and coordinates information exchange and integration.
• It provides nerve cells with electrical insulation while also removing debris.
• It gives messages from other neurons that are carried to the cell body by this neuron.

Classifications of nerves on the basis of structures

• Non polar neurons

Each neuron has a number of branching processes. Between dendrites and axons, there is no real distinction. Each process has the ability to either bring or remove an impulse from the cyton. Cnidarians (= coelenterates) like Hydra have these neurons, which are uncommon in vertebrates.

• Unipolar neurons

A single process (projec­tion) arises from cyton in such a neuron. Early em­bryos of invertebrates and vertebrates contain true unipolar neurons with an axon but no dendrite.

• Pseudo unipolar neurons 

The cyton produces a single process that divides into an axon and a dendrite. Pseudo unipolar nerve cells are the name given to such neurons. Pseudo unipolar neurons are found in the dorsal root ganglia of spinal nerves in adult vertebrates.

• Bipolar neurons

These cells possess two main processes in these synapses: an axon on one end and a dendrite on the other. The retina of the eyes, the olfactory epithelium, and the cochlear and vestibular ganglia all contain bipolar neurons (cochlea and vestibule are the parts of membranous labyrinth of internal ear).

• Multipolar neurons

There are several dendrites and an axon on these neurons. Multipolarity exists in motor neurons and interneurons. Neurons of this type are the most popular. Multipolar neurons are found in the brain and spinal cord’s grey matter.

Conclusion

Neuroglial cells in the brain and spinal cord wall have complex processes and perform supportive, metabolic, and other functions. Except at the points of synapse, they are responsible for isolating neurons from all other tissues of the body (including other neurons). Astrocytes, oligodendrocytes, and microglia are the three types of neuroglial cells. Neuroglial cells are difficult to see in routine nervous tissue preparations, and only their nuclei are visible with hematoxylin and eosin. Silver/gold impregnations of the central nervous system stained to show neuroglial cells are seen in micrographs.