The nervous system is composed of neurons and neuroglial cells. Neurons transmit sensory information to the brain and motor commands to the body. Neuroglial cells provide support and homeostasis for neurons. The document describes the main cell types of the peripheral and central nervous system, including Schwann cells, oligodendrocytes, microglia, astrocytes, ependymal cells, and how they function. It also discusses the blood brain barrier, which regulates movement between the bloodstream and brain.