From Creatures Wikia
Receptors monitor chemical levels and change the brain's behaviour - for example, shivering to relieve coldness. They are fed by emitters. One of the things that receptors do is monitor the ageing or life chemical and tell the norn when to change life stages. In some instances, receptors may control the reaction rate of a chemical reaction.
In C3, receptors were updated to bind to the reaction rate locus as well as the organ clockrate locus.
See also: