This is our final week of looking at the meninges, and our inevitable conclusion is with the Pia Mater – the “tender Mother” in contrast to the “tough Mother” that is the Dura Mater. Both the Pia and Arachnoid Mater derive from of the neural crest while the Dura is derived from embryonic mesoderm.
The Pia Mater is that most delicate innermost layer of the meninges. Composed of fibrous connective tissue covered by a sheet of flat cells, it is impermeable to fluid on its outer surface.
However, the Pia Mater allows blood vessels to pass through so nourishing the brain itself. The perivascular space between blood vessels and pia mater is proposed to be part of a pseudolymphatic system for the brain (glymphatic system). (Hladky et al. 2014: Jessen et al. 2015).