Even before you get a positive pregnancy test, your teeny-tiny embryo is making enormous growth strides. The fetal nervous system develops as follows. The fetal nervous system, which includes your baby's brain and spinal cord, is one of the very first systems to form. In fact, it's making significant progress before you ever realize you're pregnant. By the time you learn you are expecting, its neurons (nerve cells) are already being produced at a rate of about one per second after you conceive.
Around the time you find out you are pregnant, the nerve fibers connecting these neurons together will begin to grow into the embryo's brain. This is called neurulation. Over the next nine months, these nerves will continue to grow and branch out until your baby is born.
The brain and spinal cord are made up of many different types of tissues that become more specific to function during development. For example, brain tissue contains two main types of cells: neurons and glial cells. Neurons are responsible for transmitting information between your brain and other parts of your body while glial cells support neurons by providing them with an environment to grow in. Both neurons and glial cells originate from the same type of cell known as a neuroblast. As they divide and differentiate, these neuroblasts can be seen migrating toward various regions of the brain where they will eventually become part of specific circuits.
By the time you learn you are expecting, your embryo has about 200 neurons.
The embryonic period is critical in the development of the brain. The neural tube develops four weeks after fertilization. This tube will eventually grow into the central nervous system, which will include the spinal cord and brain. The neural tube, as well as a region known as the neural plate, begin to develop. As these tissues form they will become different regions of the brain and spinal cord.
During this time there are also major changes happening within the body. The embryo is growing and organs such as the heart, lungs, liver, stomach, intestines, kidneys, muscles, bones, and blood vessels are developing. The blood and lymph systems are also forming. The immune system is primarily developed during this time.
This varies greatly depending on how healthy someone was born. If someone suffers from physical or mental disabilities they may not reach adulthood. Some people can live into their 60's or 70's while others don't make it past age 20. The younger you start using drugs and alcohol the longer it takes to recover your health - this is why teens who use marijuana daily for several years experience changes in their brain structure that may affect them for the rest of their lives.
Just like with embryos, the fetus grows and develops throughout this phase of prenatal development.
The formation of your baby's brain is a complicated process that occurs throughout your pregnancy. The embryo's brain and nervous system begin to develop at just six weeks, yet the sophisticated components of the brain continue to grow and develop until the conclusion of pregnancy, when development ends around the age of 25. The major milestones in fetal brain development are as follows:
At 6 weeks, the brain consists only of a fluid-filled cavity with some nerve cells and blood vessels beginning to form connections with each other. By 8 weeks, the brain has grown in size and more neurons and brain cells are being produced every day. By 10 weeks, the fetus' brain contains many large neurons connected by thick bundles of fibers. By 12 weeks, the cerebral cortex (the part of the brain that controls thoughts and feelings) is growing in thickness. Around 14 weeks, the hippocampus (a part of the brain that plays a role in learning and memory) begins to form. By 16 weeks, the corpus callosum (a bundle of nerves that connects the left and right sides of the brain) can be seen on an ultrasound image.
Between 17 and 20 weeks, the cerebellum (a small bowl-shaped structure that helps control movement) starts to form. At about 24 weeks, you can see the first signs of brain activity. Fetuses this age will relax between 28 and 32 weeks completely relaxed and without movements associated with sleep.