Analyze the following scenario and identify the primary cellular process of brain development that has been disrupted. Explain the cascading effects this disruption would have on at least one subsequent developmental stage.

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The brain is a highly complex organ that develops in an orderly fashion, as directed by genes and the environment. There are four main stages of brain development that describe how the brain changes in morphology throughout prenatal life. Within these four main stages of brain morphological development, there are six stages describing the development of the nervous system that enable the brain to change in morphology. (Page 194 has images of the morphological changes of the developing brain). 

Stages of Brain Development

The brain starts off as a single cell: The fertilized egg, or zygote. 

-12 hours after fertilization: The zygote begins dividing such that it forms a small ball of identical cells about 200 micrometers in diameter by three days after fertilization.

-A week after fertilization: The embryo develops three distinct tissue layers that will go on to become the tissues of the body: The ectoderm, the endoderm, and the mesoderm. The nervous system will develop from the ectoderm.

-18 days after fertilization: The ectoderm thickens to develop a structure called the neural plate.

-20 days after fertilization: Cell division at the neural plate proceeds unevenly such that a neural groove forms, essentially an indentation of the neural plate.

-22 days after fertilization: The neural tube forms when the ridges of the neural groove, known as the neural crest. fuse. 

-24 days after fertilization: Development of the nervous system quickens, as the "head" end of the neural tube begins to display the beginning features of the forebrain, midbrain, and hindbrain. The neural tube becomes the interior canal within the central nervous system (CNS) carrying cerebrospinal fluid. Development of the nervous system leads to further differentiation of brain structures. 

Brain Morphological Development

In this case, development of the nervous system marks the six distinct stages of cellular development of neurons. The six distinct stages are the following; 

-Neurons form via neurogenesis, or the mitotic division of precursor cells to form neurons.

-The newly formed neurons migrate to their destinations in the developing brain via a process known as cell migration.

-The newly formed neurons become further specialized to execute their assigned tasks via cell differentiation.

-The specialized neurons network with other cells by forming synaptic connections in a process known as synaptogenesis.

-When newly formed neurons or synapses are deemed unnecessary, they are selectively removed (such cell death and synaptic rearrangement are important aspects of plasticity). 

Development of the Nervous System

Abnormalities in the development of the nervous system that are influenced by both our genes and the environment. Developmental disorders commonly manifest as behavioral abnormalities.

Developmental Disorders

Contrary to the historical belief that all brain cells are present at birth, recent research indicates that neurogenesis, the formation of new neurons, can persist into adulthood. This finding highlights the brain's ongoing capacity for change and development throughout the lifespan.

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