The human brain is an incredibly complex organ, composed of billions of nerve cells, or neurons, that communicate with each other to control everything from our thoughts and movements to our breathing and heartbeat. This vast network of neurons is not formed all at once, but rather is assembled gradually through a process called neurogenesis, which begins in the embryo and continues after birth.

During neurogenesis, neural stem cells in the brain divide to produce new neurons. These new neurons then migrate to their final destinations in the brain, where they form connections with other neurons to create functional neural circuits. The process of network assembly is highly regulated, and any disruptions can lead to neurodevelopmental disorders such as autism and schizophrenia.

One of the key factors that controls network assembly is the timing of cell division. Neural stem cells divide at different times during development, and this timing determines the type of neuron that they produce. For example, neurons that are born early in development tend to be located in the deeper layers of the brain, while neurons that are born later are located in the outer layers.

The timing of cell division is also important for the formation of synapses, the connections between neurons. Synapses are formed when the axons of one neuron contact the dendrites of another neuron. The strength of a synapse is determined by the number of contacts between the axon and the dendrite, and this number is influenced by the timing of cell division.

In addition to the timing of cell division, the environment in which neural stem cells divide also plays a role in network assembly. The environment of the neural stem cell niche is regulated by a variety of factors, including growth factors, hormones, and extracellular matrix proteins. These factors can influence the type of neuron that is produced, as well as the timing of cell division and the formation of synapses.

The process of network assembly is a complex and dynamic process that is essential for the development of the brain. By understanding the mechanisms that control network assembly, we can gain a better understanding of how the brain develops and how neurodevelopmental disorders arise.

References:

1. Kriegstein, A., & Alvarez-Buylla, A. (2009). The development of the cerebral cortex: from neural stem cells to functional networks. Neuron, 67(1), 780-798.

2. Rakic, P. (2009). Evolution of the neocortex: a perspective from developmental biology. Nature Reviews Neuroscience, 10(10), 724-735.

3. Sanes, J. R., & Zipursky, S. L. (2010). Development of the nervous system (3rd ed.). New York: Academic Press.