text: 
  """
  
  1. Because the middle fixed point is unstable. Trajectories only point to stable
  fixed points.
  
  2. The slope of dr/dt determines the speed at which the system states will evolve.
  At the nullclines dr_e/dt = 0 and/or dr_i/dt = 0. That means as we move close to
  the nullclines the dr/dt becomes smaller and smaller. Therefore the system state
  evolves slower and slower as we approach the nullcline.
  """;