Jan Evangelista Purkyně was a Czech anatomist and physiologist. In 1839, he coined the term "protoplasm" for the fluid substance of a cell. He was one of the best known scientists of his time. He is best known for his 1837 discovery of Purkinje cells, large neurons with many branching dendrites found in the cerebellum. He is also known for his discovery in 1839 of Purkinje fibres, the fibrous tissue that conducts electrical impulses from the atrioventricular node to all parts of the ventricles of the heart. Purkyně was the first to use a microtome to make thin slices of tissue for microscopic examination and was among the first to use an improved version of the compound microscope.