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Brain Development | |
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Brain Development | |
 The brain grows at an
amazing rate during development. At times during brain development, 250,000
neurons are added every minute!! At birth, almost all the
neurons that the brain will ever have are present. However, the brain continues
to grow for a few years after birth. By the age of 2 years old, the brain
is about 80% of the adult size.
You may wonder, "How does the brain continue to grow, if the brain has all the neurons it will get when you are born?". The answer is in glial cells. Glia continues to divide and multiply. Glia carries out many important functions for normal brain function including insulating nerve cells with myelin. The neurons in the brain also make many new connections after birth. |
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The nervous system develops from embryonic tissue called the ectoderm.
The first sign of the developing nervous system is the neural
plate which can be seen at about the 16th day of development.
Over the next few days, a "trench" is formed in the neural plate - this
creates a neural groove. By the 21st
day of development, a neural tube is formed
when the edges of the neural groove meet. The rostral (front) part of the
neural tubes goes on to develop into the brain and the rest of the neural
tube develops into the spinal cord.
At the front end of the neural tube, 3 major brain areas are formed: the prosencephalon (forebrain), mesencepalon (midbrain) and rhombencephalon (hindbrain). By the 7th week of development, these 3 areas divide again. This process is called encephalization. |
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Average brain weights at different times of
development:
AGE BRAIN WEIGHT (grams) 20 weeks of gestation 100 Birth 400 18 months old 800 3 years old 1100 Adult 1300-1400 |
| Brain Weight | |
(Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978) |
The top graph on the left shows the brain weights of males and females at different ages. The bottom graph shows the brain weight to total body weight ratio (expressed as a percentage). The adult brain makes up about 2% of the total body weight. |
Other excellent on-line resources:
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