He is best known for his discoveries of Purkinje cells and Purkinje fibres. Purkinje cells are large neurons with many branching dendrites found in the cerebellum. Purkinje fibres conduct electrical impulses to all parts of the ventricle of the heart. Other discoveries include Purkinje images, reflections of objects from structures of the eye, and the Purkinje shift, the change in the brightness of red and blue colours as light intensity decreases gradually at dusk. Purkyně also introduced the scientific terms plasma (for the component of blood left when the suspended cells have been removed) and protoplasm (the substance found inside cells.)