This work is based on data analysis by light, scanning, and transmission electron microscopy of surgical cases in tumors and metastases of carcinoma, thromboses, cerebrovascular malformations, aneurysms, primary hematomas, abscesses, tuberculoma cysts, Moyamoya disease, and other injurious situations such as perivascular hemorrhage, infarct, and neurotrauma in patients aged 6-89 years, with over 1,200 cerebral biopsies collected for microscopic observations. Ultrastructurally, there were identified, characterized, and compared both undifferentiated cells and well-differentiated cordocytes in different localizations, from outer cerebral cortex to choroid plexus, and in areas with old hematic masses, vasculogenic focuses, heterotopic neural tissue, encapsulation, broken arteries, and abnormal proliferations such as microtumors. We demonstrated phenotypic changes of cells, and especially, our findings shed light on the roles of these cells, which may facilitate the benefic processes and delay the pathological processes, being involved in fundamental processes of the central nervous system development. Cordocytes (which form the pia mater with blood vessels) are involved in normal corticogenesis (being demonstrated in the cerebral ectocortex), postnatally in the maintenance of appropriate pericortical microenvironment, in vasculogenesis, vasomotion, vascular repair/remodeling, inhibition of hematic invasion to brain parenchyma as physical barriers, especially in hypertensive humans, inhibition of microtumor growth and any aberrant cellular movement toward cerebral cortex, etc. The continuum of cell events could open the way for an unifying theory on special interstitial cells from the human body (interstitial cells of Cajal-like cells). This type of cell is a good candidate for stem cell therapy, cooperating with stem cells in many situations. In the last instance, the brain performance improves if its microenvironment is maintained under appropriate conditions, for which cordocytes are responsible.