Below we explain what happens in each trimester, in the development of the central nervous system:

First trimester

The development of the central nervous system begins very early during pregnancy (around the fourth week). Initially, primitive structures are formed that will develop little by little. By the end of the first trimester the cerebral hemispheres will differentiate.

During this period, neurons also begin to produce in a process called neuronal proliferation. These neurons also begin to migrate to where they belong according to their predetermined functionality (a process called migration).

Second quarter

The primitive structures formed in the first trimester evolve during this
period to differentiate the basic structures of the nervous system
central (e.g. cerebrum, cerebellum). Also during this stage, the neurons that have
migrated become specialized (according to their genetically predetermined functionality).

Third trimester

During the last trimester of pregnancy, the already formed structures of the central nervous system continue growth processes. From the neuronal point of view, myelination occurs (a process in which the axons of neurons are covered with myelin) which will be essential for correct “communication” between neurons. This process continues until months after birth.