Nervous tissue

 Nervous tissue

        This type of tissue receives impulses (sensation) especially from inside and outside of the body. In case of excitement, this type of tissue is carried impulses (waves) rapidly from one tissue to another. The nervous tissue is made up of nerve cells and nerve fibers. In addition to both them, few connective tissues named neuroglia are also found for supporting the nerve cells.                    

      A nerve cell along with all its nerve fibers is called neuron. The neuron is a functional and structural unit of the nervous tissue. Every neuron has two parts-

1.     Processes.

  • Axon.
  • Dendrites.

2.     Cell body.

  1. Processes-

Axon- The axon is conductive and efferent process and carried nervous impulses far away from cell body. It grows from axon-hillock of cell body of neuron. It is often too long and single.

          A thin (transparent) membrane is found around the axon, called axolemma that holds the cytoplasm of cell body as closed. The axon is of two types- with myelin or without myelin. The layer of white fatal substance named myelin is being covered on the axons of big and peripheral nerves. In it, there is chain of scaven cells situated in the length of axon. The outer most layer of scaven cell is known as neurilema. The myelin is divided by contracting in the middle. The place of division is called node of rainwear. This nerve helps the impulses in being distributed rapidly. Few small fibers in central nervous system and postganglionic are present myelin less.  

Dendrite- The dendrites are sanvednic and afferent process. Nissl’s granules are present in it, but these granules are absent in axon. These types of fibers are very small, but many branches grow from them. The numbers of these types of fibers vary in nerve cell (neuron).

        There are many poles present in the nerve cell (neuron) and known according to these poles. When anyone pole is absent in it, it is called apolar. The neuron having one pole is known as unipolar, having two poles is known as bipolar and having many poles is known as multipolar. An axon is found necessarily in every types of cell and all the remaining are dendrite.    

Membranes- The membranes are made up of epithelium tissue. It covers cavities and internal structures. It goes on secreting fluid for keeping its smooth and shiny surfaces as wet and preventing rub. There are following three types of membranes found inside the body-

  • Mucous membrane.
  • Serous membrane.
  • Synovial membrane.

Mucous membrane- The mucous membrane is found in food pipe or oesophagus (from mouth till rectum), respiratory duct and in the reproductive/urinary path as their layer. It is made up of cuboidal and columnar epithelium cells. A type of sticky fluid goes on secreting from few cells among them, known as mucus. The mucus is concentrated and sticky due to protein named myosin. As well as the mucus goes on accumulated in cells, the cells go on inflating (expanding) and at last are converted into flask (goblet), which are called goblet cells. After too much inflation, they are burst and release the mucus on free surface resulting it is spread on that surface. 

Serous membrane- The serous membrane is the double layered of tissue made by flat epithelium cells. Serous fluid remains filled in it. The internal layer of it is visceral layer that remains stick on the organs present inside the chest or stomach and the external layer is parietal layer. This layer remains covered such type of cavity in which organs are situated. The visceral layer is covered on the organs. It is found in the form of pleura, pericardium, and peritoneum. Due to it, the surfaces of their cavities remain smooth, shiny and wet. Only due to this serous membrane, an organ does not able to get any harm by rubbing with any other organ.

     Synovial membrane- It is a type of fibrous membrane, that remains covered with flat epithelium cells. It is a membrane that is found on the raised     parts of bone, enclosing the cavities of joints and surrounding the tendons. As a result of it, the tendons remain protected from the harmful affects (injury) of rubbing the bones with each other.

        Clean, sticky, oily synovial fluid is produced from synovial membrane, which keeps the joints smooth. It acts like a lubricant and helpful in providing strength to them.