Apparently, as the intracranial pressure increases, the brain is squeezed and catecholamines are forced out of their vesicles into the synapses and extracellular space.[5] An alternative explanation that has been proposed is that this increased in intracranial pressure transduces through the brain parenchyma through to the blood vessels producing a loss in effective cerebral perfusion. This triggers the sympathetic nervous system to secrete more norepinepherine and epinepherine increasing blood pressure and heart rate to dangerous levels to maintain cerebral perfusion.