The blood-brain barrier regulates the flow of ions, chemicals, and cells by acting as a conduit between blood and cerebral tissue. Additionally, it shields the brain against pathogen invasion and immune cell infiltration. It is composed of endothelial cells, pericytes, astrocytic end feet, perivascular macrophages, and microglial cells, which help in maintaining its integrity. There are various signaling pathways that are also involved in maintaining its integrity. The Wnt/β catenin, FZD4/FZD7, Hedgehog and TGF-β signaling pathways were evident to produce components or factors which stabilise the BBB. However, the NF-B and ERK signaling pathways caused the creation of MMPs, which increased the BBB's permeability. These functions are altered in pathological conditions like Alzheimer’s disease, and Parkinson’s disease which are also mentioned.