Brain Development Exam Notes PDF

Chapter 7 Brain Development Developing the nervous system relies on genetics and environment. Zygote is a fertilized egg. The embryo has 3 layers: Ectoderm is the outer layer and becomes the nervous system. Neural groove forms between the ridges of the ectoderm. Neural tube forms the neural ridges....

Chapter 7 Brain Development Developing the nervous system relies on genetics and environment. Zygote is a fertilized egg. The embryo has 3 layers: Ectoderm is the outer layer and becomes the nervous system. Neural groove forms between the ridges of the ectoderm. Neural tube forms the neural ridges. Endoderm: Middle, intestine. Mesoderm: Muscles and bones. Ectoderm: Nervous system, skin, and eyes. Notochord: Develops into discs between vertebrate. It releases growth proteins + signals. 18 Days: The neural crest is formed. 24 Days: When crest zips closed, central canal opens to ventricles. Development of the Nervous System 1) Neurogenesis. Production of nerve cells. Nonneural cells divide through mitosis and form ventricular zone. Cells leave the ventricular zone and become either neurons or glial cells. 2) Cell migration. Cells move away from the ventricular layer. Radial glial cells are guides for cells to migrate along. Cell adhesion molecules (CAMS) on cell surfaces guide cell migration and axonal pathfinding. Injured nerve cells react to injury in two ways: 1. Retrograde degeneration destroys the cell after an injury that is close to the cell body. 2. Anterograde degeneration (Wallerian degeneration) is the loss of the distal portion of an axon after axonal injury. The axon can regrow guided by CAMS. 3) Cell differentiation. This stage is where the cell develops its specific appearance and function. Cells express their genes in order to make proteins. Two types of influences on differentiation: Cell-autonomous differentiation is independent of other cells and are driven by genes (intrinsic organization). Neural environment differentiation, cells are affected by the influence of other cells. Cells differentiate based on their location. Regulation is the response to cell injury in development. Other cells develop and take their place. Stem cells are undifferentiated cells. They can divide and a daughter cell can assume a new cell fate. 4) Synaptogenesis. The proliferation of synapses. Extensions emerge from growth cones at the tips of axons and dendrites. Filopodia are the fine outgrowths of growth cones. They adhere to CAMS and pull the growth cones in specific directions. Chemoattractants are chemical signals that attract growth cones, and chemorepellants repel cones. Synapses form rapidly on dendrites, and the growth and connections are based off experience. 5) Cell death. Also called apoptosis. Cells have death genes that are only expressed during apoptosis. Caspases are enzymes that cut up proteins + DNA. Diablo is a protein released due to an influx of CA+. Diablo then binds to inhibitors of apoptosis proteins (IAPs). Several factors influence cell death: Neurotrophic factors (and nerve growth factor): Target cells produce these chemicals that keep cells alive and growing. 6) Synapse rearrangement. The refining of synaptic connections. In humans, synaptic remodeling thins gray matter in the cortex as dendrites prune. Chemoaffinity hypothesis says each cell has a chemical identity to guide development at a synapse. Myelination by glial cells increases the rate of axons sending messages. Multiple sclerosis destroys myelin and disrupts sensory and motor function. Environmental factors influence intellectual disability. Hypoxia is low oxygen at birth. Teratogens and viruses produce disorders. Animals with mutations are important in research development. Site-directed mutagenesis changes the sequence of a nucleotide in a gene. Knockout organisms have genes disabled. Transgenic animals has a new or altered gene introduced, which can mimic humans (mouse). Epigenetics is the factors that study gene expression without changing the nucleotide sequence of the genes.