I want to create the following two graphs.

So far I tried the following Code

GraphPlot[{"X" -> "Y", "Y" -> "Z", "X" -> "Z"}, VertexCoordinateRules -> {"X" -> {0, 0}, "Y" -> {1, 0}, "Z" -> {2, 0}}, EdgeRenderingFunction -> (If [Last[#2] == "Z", {Red, Arrow[#1]}, GrayLevel[0.5],Arrow[#1]}] &), VertexLabeling -> True, DirectedEdges -> True,] 

The Output was the following Graphic

My Questions are:

1. How do I get the arrow from X to Z as in the first Picture?

2. How can I add the wavy arrows for $S_X$ and $S_Y$?

3. How can I change the arrow head into an inhibitor sign as required for the Ic1-FFL?