Redlich-Obersteiner's Zone

The Redlich-Obersteiner's zone is a boundary of the central nervous system (CNS), separating the peripheral nervous system (PNS) and the central nervous system. The Redlich-Obersteiner's zone is located at the point of entry of the dorsal root into the spinal cord, which can be identified visually where there is a narrow zone. The narrow zone is a result of the relatively thin myelin sheath. This point is also the place where you find the last node of Ranvier before the axon enters the spinal cord.

As stated above, the Redlich-Obersteiner's zone separates the CNS and PNS. This means that at this point, you should see a Schwann cell meet with an oligodendrocyte. Recall that both of these cells produce the myelin sheath (PNS and CNS respectively).