Nervous system formation

The most critical stage of development for the embryo' s nervous system is the third and fourth weeks of pregnancy.

On day 14, the embryo looks like a little disc. The first part of the nervous system that forms is an indentation called the neural groove. Over the next 7 days, the groove deepens as the cells around it form ridges called neural folds.

By day 27, the neural folds wrap around the neural groove and form the neural tube. The neural tube will further develop into the brain and spinal cord. Structures called somites form the vertebral column, or backbone. They also help form the ribs and the muscles of the neck, arms, and legs.

The embryo' s nervous system is particularly vulnerable during the early stage of development, so an expectant mother should be careful about avoiding any substances that could potentially harm it.