action potential A sudden overshoot of membrane potential of excitable cells caused by a stimulus that is chemical, electrical, or mechanical in nature.

development Increase in weight of the organ due to an increase in size of the cells through synthesis and deposition of cell constituents such as protein, lipid, and RNA (hypertrophy).

gliogenesis Emergence of glial cells from a specific section of the neuroepithelium from where no other cells (neurons) originate.

gray matter Outer layer of cerebrum (cerebral cortex) or cerebellum (cerebellar cortex) where the majority of the neurons (about 75%) reside. The cerebral cortex is thought to be the center of all higher mental functions.

growth Increase in weight of an organ due to an increase in the number of cells through cell multiplication (hyperplasia).

growth spurt The period when the growth of a tissue is at its peak. This is the period when the tissue is most vulnerable to internal as well as external inhibiting agents.

neurogenesis Birth of neurons from the stem cells (neuroblasts) of the neuroepithelium, with each neuroblast generating a specific family of neurons.

neurotransmitter Specialized substances that mediate the transmission of nerve impulse from the presynaptic to the postsynaptic membrane and produce a postsynaptic effect (excitatory or inhibitory) by interacting with specific receptors.

The brain is the most complex of all biological tissues in nature. The complexity lies in the fact that the brain is an extremely heterogeneous tissue, composed of many constituent parts. Each part not only has its own structural organization, cellular makeup, chemical composition, and functional activity but also has a unique developmental characteristic. However, the different parts develop and maintain among themselves a highly organized coordinated system that contributes ultimately to the functioning of the brain seemingly as a single organ. It is estimated that the human central nervous system contains 11-12 billion nerve cells, each of which is capable of making up to 10,000 synaptic interconnections. According to one estimate, the number of intercellular interactions that could possibly occur within a single human brain may be greater than the total number of particles in the whole universe. It is the development of a network of this vast number of interactions that forms the basis of the functioning of the brain. Understanding the complex developmental processes of the brain and brain functions has indeed been one of the greatest challenges for man. This article explores and unveils some aspects of the complex processes of brain development in man and other animals.

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