The connective tissue in which neurons are protected is called neurogia. There are a billion or 100 million neurons in the brain. These cells do not divide, do not form synapses and do not conduct impulses. It is of four types. namely-
1. Astrocyte: It is stellate and has projections. They provide nutrients to neurons. Its abnormal division results in brain tumors.
2. Oligodendrocyte: It is small in size and has fewer projections. It forms the myelin sheath of the nerve cord.
3. Microglia: These are tiny cells. It has curved projections. They originate from the blood and cause phagocytosis.
4. Appendima: It is small cells. It has projections.