A summer student working in my lab, Ming Hong Lui from Hong Kong University (HKUST), worked on the perturbation analysis of signaling cascades and in his writeup he use TikZ to draw a nice cascade diagram which I present here.

\documentclass{article} \usepackage{tikz} \usetikzlibrary{arrows} \begin{document} \begin{tikzpicture}[>=latex',node distance = 2cm] \node (S1) {$S_1$}; \node [right of = S1] (S2) {$S_2$}; \node [right of = S1, node distance = 1.8cm] (X1) {}; \node [below of = X1] (S3) {$S_3$}; \node [right of = S3] (S4) {$S_4$}; \draw [->,very thick] (S1) to [bend left=40] node[above] {$v_1$} (S2); \draw [->,very thick] (S2) to [bend left=40] node[below] {$v_2$} (S1); \draw [->,very thick] (S3) to [bend left=40] node[above] {$v_3$} (S4); \draw [->,very thick] (S4) to [bend left=40] node[below] {$v_4$} (S3); \node [right of= S3, node distance = 1cm] (X2){}; \node [above of= X2, node distance = 1cm] (X3){}; \draw [->,very thick] (S2) to [bend left=20] (X3); \node [right of= S4, node distance = 0.8cm] (X4){}; \node [below of= X4, node distance = 1cm] (X5){}; \draw [->,very thick] (S4) to [bend left=20] (X5); \node [right of = S3, node distance = 1.8cm] (X3_5) {}; \node [below of = X3_5] (S5) {$S_5$}; \node [right of = S5] (S6) {$S_6$}; \node [right of = S5, node distance = 1.8cm] (X5) {}; \node [below of = X5] (S7) {$S_{2n-1}$}; \node [right of = S7] (S8) {$S_{2n}$}; \draw [->,very thick] (S5) to [bend left=40] node[above] {$v_5$} (S6); \draw [->,very thick] (S6) to [bend left=40] node[below] {$v_6$} (S5); \draw [->,very thick] (S7) to [bend left=40] node[above] {$v_{2n-1}$} (S8); \draw [->,very thick] (S8) to [bend left=40] node[below] {$v_{2n}$} (S7); \node [right of= S7, node distance = 1cm] (X6){}; \node [above of= X6, node distance = 1cm] (X7){}; %\node at ($(S6)!.5!(X7)$) {$\ddots$}; \draw [dashed, ->,very thick] (S6) to [bend left=20] (X7); \node [right of = S1, node distance = 1cm] (T1) {$T_1, J_1$}; \node [right of = S3, node distance = 1cm] (T2) {$T_2, J_2$}; \node [right of = S5, node distance = 1cm] (T3) {$T_3, J_3$}; \node [right of = S7, node distance = 1cm] (T4) {$T_n, J_n$}; \end{tikzpicture} \end{document}

This code draw the following figure: