Neurons are protected by the blood vessels in the brain which have a unique structure, called the blood-brain barrier. The endothelial cells of the capillaries form tight junctions, creating nearly impermeable capillaries. They only let water-soluble substances and gases pass through easily, even electrolytes and glucose pass through more slowly. The barrier is almost impermeable to plasma proteins and other large organic molecules, except for fats and fat-soluble substances.

This barrier plays a significant role in maintaining the homeostasis of the nervous system, nourishing it, and protecting it from harmful substances and pathogens.

Figure 1: Protection of the Central Nervous System