Chapter 7 quiz

Study Notes

Zygotes are fertilized eggs
Embryos have 3 layers:
- Ectoderm (outer layer) forms the nervous system
- Endoderm (middle layer) forms the intestines
- Mesoderm (inner layer) forms muscles and bones
Neural groove forms between ectoderm ridges, forming the neural tube (which becomes the neural ridges)
Notochord forms discs between vertebrate, releasing growth proteins and signals.
Neural crest forms around day 18 of development
Central canal opens into ventricles by day 24

Neurogenesis: Production of nerve cells.
- Non-neural cells divide through mitosis, creating ventricular zone cells
- Cells migrate away from the ventricular zone, becoming neurons or glial cells. Radial glial cells guide migration.
Cell Migration: Cells move away from ventricular layer. Cell adhesion molecules (CAMs) guide migration, along with axonal pathfinding.
Injured Nerve Cells: React to injury in two ways:
- Retrograde degeneration - cell destruction if injury close to the cell body
- Anterograde/Wallerian degeneration - loss of distal axon portion following injury, but the axon can regrow guided by CAMs.
Cell Differentiation: Cells develop specific appearance and function, driven by the expression of certain genes.
- Two influences on differentiation:
  - Cell-autonomous differentiation (intrinsic) - independent of other cells
  - Neural environment differentiation - affected by other cells and their location.
- Cells differentiate based on their location.
- Regulation: Cells respond to injury by other cells taking up roles
Stem Cells: Undifferentiated cells that divide and can take on new cell fates
Synaptogenesis: Proliferation of synapses
- Growth cones on axons and dendrites extend, with filopodia being fine extensions
- CAMs attract growth cones in specific directions
- Chemoattractants (chemical signals) attract growth cones, while chemorepellants repel them
- Synapses form rapidly, especially on dendrites, guided by experience.

Synaptic connections are refined
In humans, synaptic remodeling causes gray matter thinning in the cortex as dendrites prune.
Chemoaffinity hypothesis proposes chemical identity guides development at synapses.
Myelination (by glial cells) increases axon signal transmission speed, Multiple sclerosis disrupts this process.

Environmental factors can influence intellectual disability
Hypoxia (low oxygen at birth) is a factor
Teratogens and viruses can cause disorders
Genetic mutations are important for research (e.g., site-directed mutagenesis, knockout organisms, transgenic animals)
Epigenetics examines gene expression without altering the DNA sequence.