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Phil Gesotti <[log in to unmask]> wrote: <<Where is the summing node, is also a question. Is this a chemical reaction between two neurotransmitters as Duvoisin's book would have you believe? Is it the interaction of different types of receptors in the same pathway as might be suggested by STEPHAN SCHWARTZ's post?>> The five gigabillion neurons are vastly interconnected with much redundancy and alternatives in many parts of the neural networks. every square inch of skin has millions of sensors and connections. every muscle has many connections. the favorite transmitter of some synapses is dominant for some connections apparently, but scarcity of some is changed by releases of large amounts of one or a substitute chemical under certain conditions. Being startled may ascend to fright or flight adrenaline (epenephrine) overload; &c. Duvoisin argues that dopamine receptor cells in some neurons receive signals that reduce the output from that cell - that output being acetylcholine. There are mostly acetylcholine-as-neurotransmitter synapse junctions in the brain. "It is believed that dopamine acts to restrain the acetylcholine nerve cells, and that in parkinsonism the acetylcholine nerve cells are released from this restraining influence.": page 59 third edition. Parkinson's Disease. The control circuit in the model is not functional when the "static" is dominant over the dopamine-ion-transmitters are too few to make the control circuit function. This is a model of the "symptoms". The model of the disease etiology is a whole different ballgame! -- ron 1936, dz PD 1984 Ridgecrest, California Ronald F. Vetter <[log in to unmask]> http://www.ridgecrest.ca.us/~rfvetter