Stages of Neural Development

Proliferation (Stage 1) - what does it mean, where does it happen, what does it produce?

• Means cell multiplication.

• Happens in the ventricular zone (lining around the fluid space of the neural tube).
  

Produces immature neurons (no axons or dendrites yet).

Migration (Stage 2) - what does it mean? how many types?

• Immature neurons move to their correct brain location.

Must get to the right spot — they’ll stay there for life.

Somal Translocation
Glia-Mediated Migration

Somal Translocation - neuron extends a “what”? Follows “what” signals”? What do the glial cells do? Movement guided by “what”?

• Neuron extends a “foot” and pulls itself along.
  

• No physical path — follows chemical signals.
  

• Glial cells release guidance molecules (attract or repel).
  

Movement guided by the neuron’s genetic program (determines which receptors it makes).

Glia-Mediated Migration - what does it mean by a “physical path” exists? what does the radial glial cell do? Uses C.A.M.s for what? What do the glial cells do after helping?

• Physical path exists. “a physical path exists” means there is a real, structural guide, the glial fiber, that the neurons can physically move along, instead of wandering freely through tissue.

• Radial glial cells act like “tracks” for neurons to crawl along.

• Uses C.A.M.s (Cell Adhesion Molecules) to help neurons stick to the glial path.
  

Glial cells later disappear or transform after helping.

Aggregation (Stage 3) - how does the cluster of tissue form? This happen after what stage? The neuron does what?

when cells group together and stick to one another to form a cluster or tissue.

• They form organized layers or structures (like parts of the cerebral cortex).

In brain development, after neurons migrate to their destination,

Axon Growth (Stage 4) - what do the growth cones do? What does the pioneer growth cone do? What also guides the axon growth? What do the later axons do?

• Growth cones guide axons toward their targets.

• The first growth cone to move along a pathway is called the pioneer growth cone.

  • “Pioneer” = goes first, like a settler.

  • Other axons follow its path — it sends signals to guide them.

• Signals from nearby axons and glial cells also guide axon growth.

• This allows later axons to “copy” the path and reach the correct targets more efficiently.

Synaptogenesis (Stage 5) - What does it form? When does it happen? The neurons form connections, why? Why does the brain start out overconnected?

• Definition: Formation of new synapses (connections) between neurons.

• Timing: Happens after neurons have migrated and grown axons/dendrites.

• Purpose: Neurons form connections to communicate with each other.
  

Key point: The brain forms way more synapses than it needs — it starts out overconnected.

Neuron Death (Stage 6, last stage) - What is it also called? What’s the purpose?

• Also called programmed cell death or apoptosis.

• Purpose: The brain creates too many neurons, so some must die for efficiency and health.
  

Myelination (stage 8) - Think of myelin as the….? wraps around….? Without enough myelination…? This process continues…?

• Think of myelin as the insulation on electrical wires.

• It wraps around axons so signals can travel fast and smoothly.

• Without enough myelination, messages in the brain are slow or get “lost.”

• This process continues well into your 20s (especially in the prefrontal cortex).

Synaptic Pruning(Stage 7) - after neurons connect…? circuits get ….? unused circuits…? This is how the brain becomes…? It’s heavily shaped by…?

• After neurons connect, the brain has to fine-tune those connections.

• Circuits get stronger the more you use them (like practicing a skill).

• Unused circuits weaken.

• This is how the brain becomes organized, efficient, and specialized.

• It’s heavily shaped by experience, learning, and the environment.

Necrosis (Bad Cell Death – For Comparison Only) - happens after what? Why is it uncontrolled and dangerous? Only apoptosis occurs in?

• Happens after injury or stroke.

• Uncontrolled and dangerous:

  • Cell swells, bursts, and spills contents.

  • Causes inflammation and can kill nearby cells.

• Not part of normal development.

Only apoptosis occurs in healthy neural development.

Neurotrophins (Life-Giving Substances) These are protiens that what? Encourages what? Promotes what? Prevents what? Neurons that do not receive neurotrophins do what

• Definition: Proteins that promote neuron survival and growth.
  

✨ Roles of Neurotrophins

• Encourage axon growth toward the correct target.

• Promote synapse formation.

• Prevent apoptosis — neurons that receive neurotrophins survive.

Neurons that do not receive neurotrophins initiate their own death.

Role of Glial Cells define

• Radial glia: Help neurons….

• Astrocytes: Help neurons…

• Microglia: Prune…

• Oligodendrocytes: Myelinate axons to…

• Ependymal cells: Help with CSF flow and…

• Radial glia: Help neurons move and also become neurons and glia.

• Astrocytes: Help neurons connect and create a stable environment.

• Microglia: Prune synapses to refine circuits.

• Oligodendrocytes: Myelinate axons to speed up signaling.

• Ependymal cells: Help with CSF flow and brain protection.

In vivo

 = in life (inside a living organism).

In vitro

in a lab dish (outside the body).