Wiring the brain

This week we discussed brain development and examined how connections are formed and modified as the brain matures. The first step in wiring the nervous system together is the generation of neurons. In the adult, there are six cortical layers, and the neurons in each of these layers have characteristic appearances and connections that distinguish the striate cortex from other areas. Neuronal structure develops in three major stages: cell proliferation, cell migration, and cell differentiation. The choreography of cell proliferation is fascinating. It is amazing how our body is able to construct the human brain on such a detailed level.

I found Box 23.3 of special interest though-provoking. Of course, I have known that our CNS axons don’t regenerate, meaning that if my optic nerve is cut, I am not able to see ever again. However, I did not know that frogs and fish can. It left me interested as I cannot understand why humans do not have this amazing skill also. Furthermore, PNS axons are actually capable of regeneration over long distances in humans. This is pretty counterintuitive as my first thought would have been that if PNS axons are capable of regeneration, CNS axons should be too. The critical difference seems to be the different environments of the CNS and PNS, and the type of myelinating glial cell varies, oligodendroglia in the CNS and Schwann cells in the PNS.