Week 5: Development of the Nervous System & Our Genes Flashcards
Stages of CNS development
1.Gastrulation
2.Primary Neurulation
3.Secondary Neurulation
4.Neurogenesis
Gastrulation
development of germ layers
Germ layers
layers of tissue formed during early development
Types of germ layers
–Endoderm (inner tissue) →internal linings, organs
–Mesoderm (middle tissue) →skeletal system, muscles, connective tissue, organs
–Ectoderm (outer tissue) →skin and nervous system
Primary neurulation
~ 3-4 weeks formation of the neural tube
–Development of neuroectoderm→becomes the neural plate →folds inwards to become neural groove →folds fuse to become neural tube
Secondary neurulation
~4th week, the neural tube differentiates into 3 interconnected chambers
*Primary vesicles: Prosencephalon, Mesencephalon, Rhombencephalon
Neurogenesis
~ 11 weeks: structures of the CNS are formed, but amount of cells and tissue rapidly increases… through NEUROGENESIS
5 stages of neurogenesis:
✓Proliferation
✓Migration
✓Differentiation
✓Myelination
✓Synaptogenesis
Proliferation stage
production of new cells
ventricular zone
layer of cells that line the inside of the neural tube
progenitor cells
Undifferentiated cells of the ventricular zone that divide and give rise to the CNS
Progenitor cells undergo 2 types of division:
- symmetrical division
- Asymmetrical division
symmetrical division
each cell division gives rise to two identical cells; increases the size of the ventricular zone and the brain that develops from it
asymmetrical division
cell division that gives rise to another progenitor cell and one differentiated cell which gives rise to a glia cell OR neuron, which migrates away from the ventricular zone towards its final resting place in the brain
Asymmetrical division gives rise to:
▪Radial glia cells = glia that offer scaffolding to migrating neuroblasts (and intermediate progenitor cells)
▪Cajal-Retzius(CR) cells = migrate to the end of radial glia, just inside pia, important for radial migration of neurons
▪Neuroblasts = undifferentiated neurons
Inside-out development
Each new cell to be produced must pass through all the cells that came before it
Migration
via chemicals
▪Reelin &Immunoglobulins (CR cells)
differentiation
▪Differentiation of cells begin once migrated to resting place and express their genes to make proteins
▪Enables the cell to acquire distinctive characteristics ( appearance and function) within their particular region
▪Fate of the cell depends on where it “lands”
Myelination
Myelin sheaths are produced from caudal to rostral development
Synaptogenesis
Formation of synapses
Lamina of the cortex
*Cortex contains up to 6 layers
*Cell structure and organization varies between different regions of the cortex
*Morphological differences relate to functional differences
*Presence and thickness of lamina depend on section of cortex–Example: Layer V (motor) vs. Layer IV (sensory)
Is development random or programmed?
Roger Sperry’s experiments with newts proved it is not random (1943).
Laws of inheritance
–1) Law of Segregation
–2) Law of Independent Assortment
–3) Law of Dominance
law of segregation
Each inherited trait is defined by a gene pair; offspring inherit one genetic allele from each parent when sex cells unite in fertilization.
Law of Independent Assortment
Genes for different traits are sorted separately from one another so that inheritance of one trait is not dependent on inheritance of another
Law of dominance
An organism with alternate forms of a gene will express the form that is dominant.
4 bases of DNA
adenine
guanine
cytosine
thymine
4 bases of RNA
adenine
guanine
cytosine
uracil
autosomal genes
genes on autosomes
Sex-linked genes
genes on sex chromosomes (e.g., recessive gene on X chromosome, red-green colourdeficiency)
sex-limited genes
genes on autosomes influenced by sex hormones (e.g., autosomal genes influenced by hormonal conditions –e.g., bearded men)
Genetic mutation
Alterations in genetic code –there is change in DNA molecule
Epigenetics
–Changes in the expression of a gene without changing the genetic code –turning a gene on or off
–Turned on or off by Tags: acetyl groups and methyl groups
concordant
When both twins carry the disease
discordant
When only 1 twin carries the disease
candidate gene approach
examination of a single gene and it’s association with a behaviour based on theory
–APOEe4 of the APOE gene as a risk factor for Alzheimer’s disease
Genome Wide Association studies (GWAS)
examine all genes and determine differences between two groups with a particular behavior of interest
–Discover mutations at several loci for a particular phenotype
