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 most of 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.
The first three years of life are a period of incredible growth in all areas of a baby's development. A newborn's brain is about 25 percent of its approximate adult weight. But by age 3, it has grown dramatically by producing billions of cells and hundreds of trillions of connections, or synapses, between these cells. While we know that the development of a young child's brain takes years to complete, we also know there are many things parents and caregivers can do to help children get off to a good start and establish healthy patterns for life-long learning
The brain does not develop at an even pace. It tends to develop in waves with different parts of the brain developing at different times. This development takes place, however, in a predictable sequence.
Neuroscientists have shown that the brain is affected by environmental conditions throughout the entire process of development, even prior to birth. This includes the type of nourishment, care surroundings and stimulation the fetus or infant receives.
By birth the brain has developed the total 100 billion brain cells, or ‘neurons’, it possesses. However the brain is a work in progress. Most of the neurons are still immature. The cells need to be activated and the connections between neurons are weak or have not yet been formed.
At birth the infant can see, hear, smell and respond to touch, but only dimly. Almost immediately after birth the newborn’s brain begins to form trillions of connections and pathways between the neurons. These connections and pathways are vital as they enable the infant to see, hear, smell, learn and reason in a more developed way.
At conception the sperm and egg meet to form a single cell determining the genetic potential. About 60% of the genes are dedicated to brain development.
Three to four weeks after conception a thin layer of cells forms on the embryo. The cells fold and fuse to form a liquid filled tube. This is the basis of the brain and spinal cord. The embryo then starts to produce nerve cells or neurons. In the first month following conception the cells in the neural tube start to multiply at an astonishing rate, reaching a maximum of 250,000 neurons a minute. Most of the brain’s lifetime’s supply of cells is produced by six months.At 14 weeks very few of the brain cells are sparked to perform a function. The majority begin to migrate to form different areas of the brain. Most cells arrive at the correct site at the right time. Those which are damaged or go astray tend to die.
“In very rare situations some do reach the wrong location and form the wrong connections with the result later seen in eventual disorders such as severe infantile epilepsy, autism, some forms of intellectual delay and vulnerability to develop schizophrenia.”
The brain produces many more cells than it will need. By the time the fetus is twenty weeks old, about half of these cells are deliberately shed.The remaining cells are organized into forty different physical areas that will broadly govern senses and skills such as vision, language and muscle movement.
Stages of Brain Development
Brain Development in an Infant
Brain Development before birth
Repeated experiences causes the connections to become well worn pathways, permanently etched into the brain. Infrequent experiences result in the loss of developing pathways.
As the brain structure develops, the child will begin to reach the milestones associated with child development, such as grabbing an object, learning to speak, crawling and walking.
It is the combination of these neurons, synapses and pathways that will combine to form the unique structure and chemical composition of every individual’s brain.