One of the four main classes of tissues is nervous tissue. 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. A tissue is a collection of cells that are structurally and/or functionally similar.
According to theory of evolution, the first organisms which came into existence were unicellular, i.e., their bodies were made of single cells. The single–celled body of unicellular organisms perform all biological activities. Some of the unicellular organisms later evolved into multicellular organisms. Animals are multicellular organisms with their specialized cells grouped into tissues. In most animals, combinations of various tissues make up functional units called organs, and groups of organs work together as organ systems. For example, the human digestive system consists of a stomach, small intestine, large intestine, and several other organs, each a composite of different tissues. Different tissues have different structures that are suited to their functions.
Types of animal tissues In most animals, combinations of various tissues make up functional units called organs, and groups of organs work together as organ systems Animal tissues are classified into four main categories –
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
Epithelial Tissue is a thin, protective layer of cells. It covers the outside of the body and lines organs and cavities within the body including the blood vessels. They perform a variety of functions that include protection, secretion, absorption, excretion, filtration, diffusion and sensory perception etc.
Connective tissue functions mainly to bind and support other tissues. Connective tissues form a framework and support for organs and the body as a whole. They occur throughout the body. Connective tissue fibers, which are made of protein, are of three kinds : collagenous fibers or white fibers, elastic fibers or yellow fibers and reticular fibers or reticulin. Examples of connective tissue include : blood, bone, lymph.
The muscle tissue or muscles of the body form the contractile tissue and are made of muscle cells. Muscle tissue is composed of long cells called muscle fibers that are capable of contracting, usually when stimulated by nerve signals.
Nervous tissue is found in the brain, spinal cord and nerves. It is responsible for coordinating and controlling many body activities. It stimulates muscle contraction, creates an awareness of the environment, and plays a major role in emotions, memory, and reasoning.