A Brief History of the Discovery of the Neuron Cell Theory 1838 – Matthias Schleiden and Theodore Schwann proposed the cell was the basic functional unit of all living things BUT it was widely believed this did not apply to the nervous system Development of the Achromatic Lens 1820’s Johannes Purkinje 1832 – Purkinje began examining thin sections of nervous tissue First neurons to be identified: Purkinje cells found in the cerebellum Otto Friedrich Carl Dieters 1863 - Further improvements in microscopy enabled Dieters to produce the most accurate description yet of a nerve cell Referred to the axon as the “axis cylinder” and the dendrites as “protoplasmic processes” The Great Debate Debate among researchers raged on about the organization of the nervous system Reticularists believed the nervous system consisted of a large network of tissue or (anastomoses) formed by the fused processes of nerve cells Neuronists argued that the nervous system consisted of distinct cells Joseph von Gerlach A reticularist 1871 - Used gold chloride or carmine to stain nerve tissue Concluded: “the finest divisions of the protoplasmic processes ultimately take part in the formation of the fine nerve fibre network which I consider to be an essential constituent of the gray matter of the spinal cord.” Camillo Golgi 1873 - Developed a new staining technique which involves hardening of tissue in potassium bichromate and ammonia, followed by immersion in silver nitrate Still thought his observations confirmed the “nerve network” organization of the nervous system Wilhelm His, Sr. 1880’s studied embryological development of the central nervous system “I consider as a definitive principle the theorem that every nerve fiber originates as the outgrowth of a single cell.” His micrograph of the neuroblastic cells with processes growing toward the surface (human embryo at four weeks) Santiago Ramon Cajal 1887 used Gogi’s method of staining nervous tissue with the addition of immersing the tissues in fixative and silver nitrate a second time Observation of the basket cells of the cerebellar cortex: “The special character of these cells is the striking arrangement of their nerve filament (axon), which arises from the cell body but also very often from any thick, protoplasmic expansion (dendrite).” The Big Breakthrough! The twentieth century invention of the electron microscope allowed researchers to examine nervous tissue in greater detail. Electron micrograph (right) shows clusters of vesicles docked at the presynaptic membrane. Scanning electron micrograph (below) shows vesicles in the process of fusing with the presynaptic membrane The Neuron Doctrine The neuron is the fundamental structural and functional unit of the nervous system. Neurons are discrete cells which are not continuous with other cells. The neuron is composed of 3 parts – the dendrites, axon and cell body. Information flows along the neuron in one direction (from the dendrites to the axon, via the cell body). Current Vocabulary The term “neuron” was introduced in 1891 by Heinrich Wilhelm Gottfried von Waldeyer-Hartz (A) “Axis cylinder” was named “axon” by Rudolph Albert von Kolliker (B) “Protoplasmic processes” were called “dendrites” by Wilhelm His Sr. (C) And finally, “synapse” was coined by Sir Charles Sherrington in 1897 (D) A B C D .