Structural Characteristics: The particular type of tissue, which forms the nervous system, is called nerve tissue. Receiving stimulus from the environment, the nerve tissue transmits it within the body and accordingly appropriate responses are created. The special type of cell which forms the nerve tissue is called nerve cell or neuron.
So a neuron is the structural and functional unit of nervous system. It is ectodermal in origin. Neuron or nerve cells can receive various types of external and internal stimuli or nerve-sensation and can transmit those inside the body.
Structure of a Neuron: A mature neuron has three parts These are:
a) Cell body: The cell body is generally polygonal and nucleated. The cytoplasm of the cell contains mitochondria, golgibody, ribosome, endoplasmic reticulum etc. But as there is no active centriole in the cytoplasm of neuron, the neuron cannot divide.
Function: Originating from the cell body, two or more branches transmit stimuli or nerve impulse to the neuron’s cell body. Generally they are one or several in numbers and present opposite to the axon.
b) Axon: From the neuron’s cell body a long fibre branch carries nerve impulse towards dendrite of the next neuron. A neuron has only one axon. Between the with the dendrite of the other. It is called synapse. Through the synapse stimuli of a nerve is transmitted from one neuron to another.
Location: Nerve tissues are located within the nervous system. There are innumerable neurons is the nerve tissue of any animal.
Function:
- To receive stimuli and create proper sensation.
- To store memory in higher animals.
- To control the works of different organs of the body and coordinate their activities.
c) Organs: An organ is a part of animal body formed by the combination of one or more than one type of tissues performing a particular function is called an organ. That is to say, in any organ there may be one or more than one type of tissues and the organ can perform a particular work. The branch of biology where organs are discussed is called anatomy.
Necessary Organs of Human Body: According to location there are two types of organs in human body. The branch of Biology, where the morphology of external organs like eye, ear, nose, hand, foot, head etc. are discussed, is called Morphology.
Again, the branch of Biology where the internal organs of the organism are discussed in detail is called Internal Anatomy. Eye, ear, nose, hand, foot, head etc. are external organs and stomach, duodenum, ileum, rectum, heart, liver, pancreas, spleen, lung, kidney, testis, ovary etc. are internal organs of human body.
