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.

Neurogenesis in Adulthood

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.

Disruption in Neural Development

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). 

Brandeis University

Google

Macalester College

California Polytechnic State University, San Luis Obispo

- Evolution of the Brain and Behavior
- Life-Span Development of the Brain and Behavior

Evolution and Development of the Nervous System

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Plasticity is how the brain is able to learn and adapt to environments. It exists throughout a person's lifetime, though it tends to be more active in early development when the brain is still forming. Plasticity is one of the key concepts within behavioral neuroscience that affects nearly all systems of the brain and brain functions.

Plasticity

Stages of Brain Development

Experience and the environment regulate gene expression in brain development by helping to shape behaviors and a person's surroundings and vice versa. This is called epigenetics.

Genes and Experience Guide Brain Development

- visual deprivation

- early exposure to visual patterns

Individual Differences in Experience Affect Brain Development 

- Memory Impairment

- Alzheimer's Disease 


Brain Changes Due to Aging

The process in which physical/behavioral changes of a population occur over long periods of time. Evolution is a scientific theory that for over the last 150 years, scientists have gathered an overwhelming amount of evidence that supports this theory.  

Evolution 

- Development begins from common structure (dorsal tube)
- Symmetry within brain structures (bilateral symmetry) 
- Construction of spinal nerves with spinal cord (segmentation)
- Communication between brain and spinal cord (hierarchical control) 
- Differentiated neural systems 
- Localized functions

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