Neuroglia (or neuroglial cells)

These are specialized cells found in the brain and spinal cord, supporting the body. They are divided into two major categories: Macroglia (= large glial cells) and microglia (= the neurons and their fibers. Neuroglia is more than one-half the volume of neural tissue in human small glial cells). Macroglia are of two types:

1. Astrocytes. There are two types of astrocytes: Fibrous astrocytes are found chiefly in white matter, and Protoplasmic astrocytes occur chiefly in grey matter. The astrocytes provide the repair mechanism and replace lost tissue.
2. Oligodendrocytes. They are found in close association with large nerve cells, and in rows between bundles of fibers in the white matter. They play a metabolic role in the formation and preservation of the myelin sheath of the nerve fibers in the central neural system.

Microglia are found diffusely through both grey and white matter. Microglia are mesodermal in origin. These cells are the scavengers of the neural system and become phagocytic in case of injury and death of the other elements.  Ependymal cells and neurosecretory are also part of neural tissue.

Ependymal Cells

These cells form a cellular membrane that lines the ventricles (cavities of the brain) and the central canal of the spinal cord. Their free surface bears numerous microvilli and cilia. The microvilli help in the absorption of cerebrospinal fluid. The movements of cilia contribute to the flow of cerebrospinal fluid.

Neurosecretory Cells (Neurosecretory neurons)

These occur in the neural system. The hypothalamic neuro-secretory cells are present in the hypothalamus (part of the brain). They release neurohormones (releasing factors) into the bloodstream. These hormones are carried to the anterior lobe of the pituitary gland where they regulate the secretion of hormones such as ACTH, TSH, GH, LH, FSH, and prolactin.

All living organisms are made of cells. A unicellular organism has a single cell in its body, i.e., a single cell performs all basic life activities. However, in multicellular organisms, there are millions of cells. Most of these cells are specialized to carry out only a few functions efficiently. These functions are taken up by a distinct group of cells. Thus, it can be said that there is a division of labor in multicellular organisms.

A tissue is a group of cells that are similar in structure, origin, and function. The term ’tissue’ was given by Bichat. The branch of science dealing with the tissues is called ‘histology’. Mayer introduced the term histology. Malpighi is considered the “founder of histology. Broadly animal tissues are classified into four types: epithelial, connective, muscular, and neural.