Chapter 4: Development Flashcards
Describe the three cell layers of an embryo and how it becomes a brain.
A human embryo will develop three cell layers 1) endoderm, 2) mesoderm, and 3) ectoderm
Ectoderm: outer layer, becomes the nervous system
- thickening cell layers form a groove which becomes the midline - the neural tube forms the neural ridges - the anterior part of the neural tube has three subdivisions: the forebrain, the midbrain, and the hindbrain
A developing human is called an embryo for the first 10 weeks, then is called a fetus
Name and describe the 6 stages of neural development
- Neurogenesis: mitosis produces neurons from nonneuronal cells
- Cell migration: cells move to establish distinct nerve cell populations
- Cell differentiation - cells become distinctive neurons or glial cells
- Synaptogenesis: establishment of synaptic connections
- Neuronal cell death - selective death of many nerve cells
- Synapse rearrangement - loss or development of synapses, fine-tuning
Describe cell proliferation.
Cells divide in a process called mitosis, which takes place within the ventricular zone, a region lining the cerebral ventricles that displays mitosis, providing neurons early in development and glial cells throughout life.
Eventually, cells leave the ventricular zone and begin transforming into either neurons or glial cells.
Describe cell migration and cell differentiation
During cell migration, cells move away from the ventricular layer. When cells reach their destinations they begin to express particular genes, to make the proteins they need.
This cell differentiation allows a cell to acquire its specific appearance and function and begin synaptogenesis.
Describe cell-cell interactions in neural development
Cells in the developing brain send signals and shape the development of other cells. Cell-cell interactions are the developmental process in which one cell affects the differentiation of another.
If cells have not differentiated and can be placed in a particular brain region, they will differentiate
Stem cells are undifferentiated cells.
Adult neurogenesis is
the generation of new neurons in adulthood, primarily in the dentate gyrus.
Describe why cell death is an important part of the neural development process
Cell death, or apoptosis, is an important part of brain development. Cells undergo this process as a result of complex interactions with other cells.
Certain death genes are only expressed when a cell is undergoing apoptosis, and are important for downstream effect on other cells.
Chromosomes carry death genes. Interference with these genes causes fetal mice to grow brains that are too large to fit inside their skulls.
Describe the process of synapse rearrangement
After the period of cell death, neurons grow longer and more elaborate dendrites, each with many new synapses
Some of these will be lost and many more created in the process of synapse rearrangement, or synaptic remodeling.
In human cortex there is a net loss of synapses from late childhood through midadolescence. the thinning process continues through maturation, reaching the prefrontal cortex last, which may contribute to teenagers’ impulsivity.
What are neurotrophic factors and why are they important
(also simply called a trophic factor) They are a target-derived chemical that acts as if it “feeds” certain neurons to help them survive. Neurons that gather insufficient trophic factors die.
Why may teenagers have a lack of self-control?
In synaptic remodeling, there is a thinning of the cortex as pruning of dendrites and axon terminals progress.
Thinning process continues in a caudal-rostral direction during maturation, so the prefrontal cortex matures last.
Differentiate between a genotype and a phenotype
A genotype is the sum of an individual’s intrinsic, genetic information.
A phenotype is the sum of an individual’s physical characteristics.
Genotype is constant but phenotype changes constantly. Phenotype is determined by a combination of genotype and extrinsic factors - different phenotypes of the nervous system produces different behaviors
Define and describe the effects of PKU on the brain.
Phenlyketonuria (PKU) is a disorder of protein metabolism
- absence of an enzyme that metabolizes phenylalanine
- if not corrected by diet, high levels of phenylalanine will cause intellectual disability
- the interaction of genes and environment is important - intellectual disability occurs only in the presence of phenylalanine.
Describe epigenetics and give an example
Experience regulates gene expression in the brain.
Epigenetics is the study of factors that change gene expression, without changing the gene sequences.
- maternal care is important epigenetic factor - genetically identical male mice raised by mothers of a different strain show differences in behavior
What is methylation?
Methylation is a chemical modification of DNA that doesn’t affect the nucleotide sequence but makes the gene less likely to be expressed
- poor maternal care induces methylation of the glucocorticoid receptor gene in the brain - rodent pups become hyperresponsive to stress for the rest of their lives - in humans, this same gene is methylated in those who suffered childhood abuse
What is the most inherited cause of an intellectual disability?
Fragile X syndrome. A condition produced by a fragile site on the X chromosome that seems prone to breaking because the DNA there is unstable.
- elongation of face, prominent ears and prominent chin - syndrome affects mental development by blocking the normal elimination of synapses after birth.
