At birth, the brain is nearer to its adult size than any other physical structure. The human brain has 100-200 billion neurons, which store and transmit information. Since a given neuron may have hundreds of synapses, the number of synapses, or connections, in the brain is obviously over 200 billion. Neurons that are stimulated by input from the environment continue to establish new synapses, while those that are seldom used die off. Myelin has a white appearance.
Myelinization occurs both before and after birth and can be affected by diet.
Glial cells multiply dramatically from fetal age four months to the child's second birthday. The cerebral cortex is the largest part of the human brain, and it is the last of the brain structures to stop growing. Within the cortex, the last part to develop and myelinate is the frontal lobe, which is responsible for thought, consciousness, planning, and socially acceptable behavior in general. Humans have two hemispheres which control the opposite side of the body. We have a property of the brain called lateralization, which means that the two sides do different things.