Sleep

Abstract

The biological phenomenon of“sleep” is an instinctual action, an active process, which represents an energy-restoring function for the organism, and which is entirely governed by the mid-brain. W. R. Hess showed in animal experiments that cats whose mid-brain region was electrically stimulated fell asleep, and Jouvet succeeded in isolating the putative neurotransmitter responsible for releasing sleep: it turned out to be serotonin (5-HT). He was also able to show that para-chlorophenylalanine, an antagonist of 5-HT-synthesis, could stop an animal from falling asleep. The precursors tryptophan and 5-hydroxytryptophan, both of which can cross the bloodbrain-barrier (see Fig. 2), are converted to serotonin in the nerve cell. Release of the neurotransmitter then induces sleep. The switching off of the conscious waking state goes hand in hand with a total biological transformation of the whole organism: the phase of sympathetic performance which is maintained by the transmitter noradrenaline (NA) is replaced by the energy-restoring recovery phase: blood-pressure is lowered, the pulse is slowed, breathing becomes shallower and the painthreshold is raised.