Nervous Tissue

A tissue is a collection of cells that are structurally and/or functionally similar. One of the four main classes of tissues is nervous tissue. The nervous system consists of the central and the peripheral nervous system. The central nervous system consists of the brain and the spinal cord. The basic nervous system is made up of nervous tissue, whose basic unit is the nerve cell, also known as neuron. Neurons are specific cells and the structure of neurons is what basically makes up the structure of the nervous tissue. Given below are details regarding the structure and function of nervous tissue.

Nervous Tissue Structure

As already discussed, nervous tissue location cannot be specified, as nerves are present all over the body, although the central nervous system only comprises the brain and spinal cord. The neurons vary in length depending on their location and function. Also, depending on the site of exit of axon and dendrite, the neuron can be classified as unipolar, bipolar or multipolar. A neuron's structure consists of three parts which are as follows:

Dendrite: These are the cell extensions that arise from different parts of the soma or the cell body. These are basically branches of the cell, which further branch out to form what is known as a dendritic tree. These help to conduct electrochemical inputs that are received from adjacent neurons via the synapses. This is the part of the neuron that plays an important role in integrating synaptic inputs and deciding to what extent the action potential is to be produced.

Soma: The soma or cell body is the central part of the neuron that contains the nucleus and connects the dendrites to the axon. If you were to study the histology of nervous tissue, then you'll realize that the size of soma varies from four to a hundred micrometers in diameter, and the size of the nucleus varies from three to eighteen micrometers in diameter. The size of the soma is dependent on the size and length of the neuron. This is the part of the neuron where most of the protein synthesis occurs.

Axon: The axon is a thin and fine cable like projection that can be thousands of times longer than the diameter of the soma. The axon is the part of the nervous tissue that is responsible for carrying nerve signals and messages away from the soma towards the other neurons. The starting point of the axon, that is, the part that emerges from the soma, is the part that is known as axon hillock and it has the highest density of sodium channels that are dependent on voltage. The axon is covered by myelin sheath and neurilemma, which contain Schwann cells. The myelin sheath is interrupted by nodes of Ranvier. The axon terminal has synapses which contain neurotransmitters, which is one of the nervous tissue characteristics.

Nervous Tissue Function

So, how does the nervous system function? The functioning of the nervous system is dependent on the functioning of the nerve cells. The nervous tissue function is propagating messages from one part of the body to another. This includes taking in a sensory input, integrating it and acting on it. This helps to bring about movement of muscle, mental activity and overall homeostasis of the body. The signal is received through the dendrites and then, is transmitted to the cell body, from where it moves further through the axon. The axon splits into axon terminals, which lead into synapses which are rich in neurotransmitters. This then makes the signal reach the dendritic tree of the next neuron and so, nerve impulses travel from one nerve to another and so, from one part of the body to another.

This was all about the structure and function of nervous tissue. There are a few nervous tissue diseases which leads to various peripheral and central nervous system disorders. However, that happens only when there is a disease or injury that leads to disturbances in the functioning of the nervous system.