The tissue of the central nervous system comprises two classes of cells that may be broadly classified as neurons and glia. Neurons are the anatomic, functional, and trophic units of the brain. Despite great variability in size and shape, all neurons share common morphologic features; the key elements of a highly complex communication network. Neurons, which have a dynamic polarization, serves as the major signaling unit of the nervous system. They are responsible for receiving sensory input from the external world; for sending motor commands to our muscles and also for transforming and relaying the electrical signals at every step in between. The human brain contains about 1 x 10¹¹ neurons, each being able to contact at least 10,000 other neurons. Human Mesencephalic Neurons in culture provide an invaluable tool for understanding physiological and pathophysiological relevance in brain function and disease.