So we spoke about rats which were actually needed to activate mex, and then the mechs are needed to activate hercs. And these irks are protein kinases that move into the cell, into the nucleus of our cell, and inside the nucleus, they essentially activate these transcription factors which increase the rate of expression of genes and that ultimately allows the cell to produce many proteins that ultimately allow the cell to grow and divide, which is what the physiological effect is in this particular case. So when we spoke about this pathway we said that the physiological effect might be, for instance, actually sealing off that cut that we might experience on the epidermal cells of our skin. So we see that a protein kinases are used by all four pathways that we discuss, and this implies that they play a crucial role in this signal transduction pathway and actually carrying out that particular type of physiological effect. Now, secondary messengers are also used by each one of these four different types of pathways. And we said that all these signal pathways use these secondary messengers to basically amplify that initial signal.