Prenatal Brain Development – What’s Happening In the Womb
It’s so amazing that a tiny, fertilized embryo eventually develops and grows into a full-grown human being, complete with a nerve network, a giant impulse superhighway, the spinal cord, and an incredibly complicated hub of neurons called the brain. During prenatal brain development, a baby’s brain goes from zero neurons to 100 billion!
At three weeks of gestation, the embryo consists of three layers; the outer ectoderm, the middle mesoderm, and the inner endoderm.
Nerve cells are derived from a specialized type of cell from the ectoderm. The growth cones in these cells are responsible for the formation of axons and dendrites, parts of the nerve cell.
At The Beginning
The brain cells begin to divide at the tip of the embryo and form a tube. This neural tube then expands slowly to form the brain and the spinal cord. At first, the brain cells start to multiply quickly but the pace slows down during the second trimester.
During the third week of gestation, the neural groove is formed which will later develop into the primary brain structure. This groove will curl up to form the neural tube. The neural tube is the precursor of the spinal cord. Then the neural crest cells begin to form.
It is these neural crest cells that differentiate into brain cells and nerves. By the fourth month, various sections of the human brain will become established and distinct. Five brain vesicles can be seen clearly at this stage. These vesicles eventually become the forebrain, the midbrain, and the hind brain.
After 6 weeks, certain hormones get released that differentiate the pace of prenatal brain development between boys and girls. In the second trimester, the brain is fully developed but still has not reached full size, for the sake of the mother.
Six distinct layers are now established within the cerebral cortex and almost all of the neurons within the central nervous system are present. The development and wiring of the baby’s neural ‘circuitry’ continue to develop as it begins to program itself for life outside the womb. The baby begins to develop taste and smells sensations, and can recognize certain familiar sounds.
In the third trimester, to accommodate its increasing size, the brain starts forming folds. During this period of prenatal brain development, the amount of information being stored begins to skyrocket. During the 8th month of pregnancy, the nervous system is still increasing its connections and receiving more and more sensory input and developing more motor control. At the ninth month of pregnancy, refinement of motor and other neuronal connections takes place. By the time of birth, the baby is fully capable of breathing, sucking, and remembering his or her mother’s sounds, smell, and familiar tastes.
When the neural tube is formed there are only 125000 cells but by the time of birth, the total number of nerve cells reaches 100 billion. This means these cells develop at a rate of 250,000 cells per minute! Prenatal brain development occurs at a breakneck pace, so if anything goes wrong during this time due to disease, drugs, or poor nutrition, the development of the baby’s brain is significantly affected.