Cycles and rhythms appear in all living beings. All human activities also follow cycles.
For example, in the vegetative activities we recognize a) short cycles such as breathing, circulation, and digestion: b) daily cycles such as alternating sleep and vigil; c) monthly cycles such as menstruation; and d) cycles of longer biological stages such as childhood, adolescence, etc.
Each center has its own distinct rhythm, but working together they combine to set an overall rhythm for the whole structure. Moreover, the cycles for the centers vary in a structural relationship and even though the cycle length is different for each center, they work together in a system of general compensation. This system of cyclical compensation reveals the variations in equilibrium of the total structure in time. There are biorhythms present in the functioning of the centers of response, the levels of consciousness, and the behavior in general.