1. Chapter 2: Brain Development
TJHSST Neuroscience Society
Prepared by Usnish Majumdar

2. Development First neurons must be created (differentiated cells)
Neurons must then migrate
Axon-dendrite migration and connection occurs

3. 3 Layers of Embryo Ectoderm (“ecto” latin = outside) Neural Tissue
Skin
Neural Tissue
Mesoderm (“middle” latin = middle)
Endoderm (“endo” latin = within)

4. Neural Tube Formed 3-4 weeks after conception
Two parallel ridges form from ectoderm tissue
Hollow
Forms spinal cord and Brain

5. Cell Differentiation Most embryonic cells are pluripotent stem cells
A variety of chemicals signal cells to turn into specialized cells
Ectodermal cells are inhibited by molecules, signalling a development into neural cells and not skin cells
After neural cell determination:
Sonic hedgehog – protein secreted from mesoderm
Higher concentration = glial cell
Lower concentration = motor neuron
Even lower concentration = interneuron

6. More Cell Differentiation (Yes, this is important)
Signals help determine the specific neurotransmitters that can be used by a neuron
If neurons are cultured by themselves = norepinephrine
Cultured with cardiac tissue = acetylcholine
Based on different genes turning off and on

7. Neuronal Migration in The Brain
Neurons produced in center of tube, migrate outward
Ventricular zone -> Marginal zone
Migration prominent in cortex
Mechanisms
Neurons migrate along fibers to destination
inhibitory interneurons migrate tangentially
External forces that can disrupt proper neuronal migration:
Alcohol, Cocaine, Radiation, etc.

8. Connections Axons travel long distances until they find dendrites
In the case of a motor neuron, axon may travel from spinal cord to foot

9. Axon Growth Controlled by Growth Cone
Contains receptors for certain signaling proteins
Signaling proteins (actually classes of proteins)
Netrin
Semaphorins
Ephrins
Possible effects
Move forward
Stop
Recoil
Change Direction
Axon meets Dendrite and forms synapse
Additional molecules help with target recognition
Last process is the wrapping of axon in myelin

10. Cervical
Thoracic
Lumbar
Sacral

11. Paring Back
Neural network is ‘pruned’ to create a more efficient and accurate system (too many connections at first)
Apoptosis: programmed cell-death
AP Biology: regulated by several proteins
Neuron doesn’t receive enough trophic factor to deter these proteins, it dies
Each trophic factor supports a specific group of neurons
Ex: nerve growth factor = sensory neuron survival

12. Critical Periods
Important period when nervous system must obtain certain critical experiences.
“use it or lose it”
Enriched environments bolster brain development

13. Development Continues
Even in your late teens, your brain is still maturing.
Frontal lobe is last to become connected with myelinated axons
Judgement, insight, and impulse control
…college students …

14. Quiz: 5 minutes, 15 Questions