Making nerve cells
Once the embryo has marked out its future brain and spinal cord, it can start to make vast numbers of neurones. At times, 4000 new neurones are made every second. They will eventually connect to form huge networks, allowing the brain and body to communicate via electrical signals. The embryo also needs to make billions of glial cells, which help to guide these networks and provide the neurones with support. They then glue the networks together.