The Development of the Human Brain

Two types of cells are important here. The first type, glial cells, make up 90 percent of the brain cells inside your child�s head. They give the brain its structure and help the neurons correctly process information. It�s a good name; glial is a Greek word for glue. The second type of cell is the familiar neuron. Though they do a lot of your child�s thinking, neurons make up only about 10 percent of the total number of brain cells. That�s probably where we get the myth that you use only 10 percent of your brain.

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One neuron, 15,000 connections

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So how do cells turn into brains? Embryonic cells are manufactured into neurons in a process called neurogenesis. This is when the baby would like to be left alone, in the first half of pregnancy. Then, in the second half of pregnancy, the neurons migrate to the region they eventually will call home and start wiring together. This is called synaptogenesis.

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Cell migration reminds me of when tracking bloodhounds are suddenly loosed from the sheriff�s truck to pick up the scent of a criminal. Neurons bolt out of their ectodermal cages, crawling over one another, sniffing out molecular cues, pausing, trying out different pathways, slithering helter-skelter throughout the developing brain. Eventually they stop, having arrived at a destination that may be pre-programmed into their cellular heads. They look around their new cellular digs and try to hook up with the neighbors. When they do, tiny, lively gaps between neural cells are created, called synapses (hence the term synaptogenesis). Electrical signals jump between the naked spaces to allow neural communication. This final step is the real business of brain development.

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Synaptogenesis is a prolonged process, for an easily understood reason: It is ridiculously complex. A single neuron has to make an average of 15,000 connections with the locals before its wiring job is over. Some neurons have to make more than 100,000 connections. That means your baby�s brain has to lash together an astonishing 1.8 million new connections per second to make a complete brain. Many of the neurons never complete the process. Like post-sex salmon, they simply die off.

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Even given this incredible speed, baby brains never make the birth deadline. About 83 percent of synaptogenesis continues�afterbirth. Surprisingly, your baby girl�s brain will not completely finish its wiring until she is in her early 20s. Boys brains may take even longer. In humans, the brain is the last organ to finish developing.

Notes:

A fascinating description of a process that begins before birth and continues into our 20s.

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Brain Rules for Baby: How to Raise a Smart and Happy Child from Zero to Five

Books, Brochures, and Chapters>Book: Medina , John (2010-10-12), Brain Rules for Baby: How to Raise a Smart and Happy Child from Zero to Five, Pear Press, Retrieved on 2011-07-27

Folksonomies: parenting pregnancy babies child development