Friday's discussion on phantom pain led nicely into the discussion of reflex action, which, in turn, brought to mind the chemical principle that so many students "just can't" seem to fully internalize: LeChatelier's Principle. But more on that shortly.

The nervous system was described as constantly comparing actions with expectations. Mismatches produce dissonances: discomfort, pain or nausea.

So, the description of phantom pain as a "dissonance" between a motor action and a sensory response that doesn't match makes a lot of sense . . . and may answer a question I've held that has gone unanswered for a long time.

This same idea of the nervous system constantly making comparisons also explains how reflexes work. The same can seem to be said for nonsentient physical systems. Hence, . . .

LeChatelier postulated that all chemical systems at equilibrium when put under a stress will react so as to minimize the stress. For instance, if the temperature rises, the system moves in an endothermic manner so as to absorb the extra heat and lower the temperature. If an acid is added, the system tries to generate more base to neutralize the acid (minimize the pH change).

The reflex action was described in terms of a sensory nerve bundle that measures the length of a muscle. If the muscle lengthens, the nerves enervate to contract the muscle -- in order to maintain the original length -- or "minimize the change" like LeChatelier's Principle.

So, our nervous sytems have evolved according to simple physical principles, which, to a degree, is a bit "unnerving" to realize.