Drawing from monkey retina, Boycott, 1974

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Drawing from monkey retina, Boycott, 1974
Drawing from dog olfactory bulb, Golgi, 1875
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Development of the Nervous System

• Development of neurons in
• neural tube (brain and spinal cord)
• peripheral neurons (neural crest)
• peripheral neurons (ectodermal placodes)
• Axons and dendrites grow out.
• Axons and dendrites find their
  right partners
• Axons and neurons form
  functional synapses
• The human brain has 1011 neurons, each with
  gt1000 connections. The brain is hard wired (or
  is it?)

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Important questions about the nervous system

• How are the neurons specified?
• How do axons grow out?
• How are final appropriate connections made?
• Are they permanent?

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Neurons are specified by their birthday
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and their position in fields of paracrine
morphogens
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Important questions about the nervous system

• How are the neurons specified?
• How do axons grow out?
• How are final appropriate connections made?
• Are they permanent?

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Microfilaments (actin)
Microtubules (tubulin)
http//www.ohsu.edu/croet/faculty/banker/neurons/m
ovies/axon_uniform.mov http//www.ohsu.edu/croet/f
aculty/banker/neurons/movies/axon_patterned.mov
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Directed movement

• Contact guidance
• http//www.ohsu.edu/croet/faculty/banker/bankerlab
  movies.html
• Guidance by other pioneer cells due to
  homophilic adhesion molecules like N-CAM and
  cadherins (more than 100 cadherin genes expressed
  in human brian)
• Chemotaxis

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The Neurotrophins
Rita Levi-Montalcini
Knockout mice?
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Important questions about the nervous system

• How are the neurons specified?
• How do axons grow out?
• How are final appropriate connections made?
• Are they permanent?

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Formation of Neural Maps Outgrowth of the
Retinal Ganglion Cells to the Optic Tectum
(lateral geniculate nucleus in mammals)
optic chiasma
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Stage 23 normal projection Stage 28 inverted AP
projection Stage 32 both projections inverted
N nasal anterior T temporal posterior
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repulsive
Matching coordinates of ephrin receptor (retina)
and ephrin (tectum) concentration.
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Temporal axons
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Important questions about the nervous system

• How are the neurons specified?
• How do axons grow out?
• How are final appropriate connections made?
• Are they permanent?

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Activity Dependent Remodeling neurons that fire
together, wire together