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George E. Carvell, PhD, PT   University of Pittsburgh
CEREBELLAR CIRCUITRY: Simple and Complex Purkinje Cell Spikes
Simple spikes are due to Parallel Fiber Activation of Purkinje Cells. Granule cells are the source of parallel fiber axons. Granule cells are tonically activated by mossy fiber input. Complex spikes are due to direct activation of Purkinje cells by climbing fibers. Climbing fibers originate in inferior olivary neurons. Complex spike discharge is infrequent compared to Simple spikes.
Fig 31-7 W.T. Thach, The Cerebellum, Chapter 31 IN: Medical Physiology V.B, Mountcastle, ed. Vol 1 St. Louis: C. V. Mosby,  pp.837-858, 1980.
Thach Fig 31-7,  p 851