<P> There are receptors and other systems in the body that detect a decreased volume or an increased osmolite concentration . They signal to the central nervous system , where central processing succeeds . Some sources , therefore , distinguish `` extracellular thirst '' from `` intracellular thirst '' , where extracellular thirst is thirst generated by decreased volume and intracellular thirst is thirst generated by increased osmolite concentration . Nevertheless , the craving itself is something generated from central processing in the brain , no matter how it is detected . </P>
when blood volume and pressure is low which part of the brain triggers the thirst response
central nervous system