ess - construction of a neuroblast into a mature neuron

Once the neuroblast has entered a post mitotic
state the outgrowth of neuronal processes
begins

1.groiNeurites – small extensions that protrude from the immature neuron
(neither axon or dendrites)
2. Microtubule and actin cytoskeleton and other proteins are redistributed (Par 3)
3. Single process – axon (apical domain) – express Tau (red)
4. Remaining processes become dendrites (basal domain)

growth cone

Growth cone – specialized structure at the tip of the
extending (growing) neurite
• Explore the external environment
• Determine the direction of growth
• Guide the extension of the process in that direction

lamellipodium

Lamellipodium – sheetlike expansion of the growing
axon
• Filopodia – fine processes that extend from each lamellipodium
• Different cytoskeletal molecules than the axon shaft
• Once a growth cone reaches and recognizes an
appropriate target it is transformed into a presynaptic
ending for an axon

actin cytoskeleton

Actin cytoskeleton (actin) – regulates changes in
lamellipodal and filopodial shape for directed growth

microtubule cytoskeleton

Microtubule cytoskeleton (tubulin) – responsible for
the elongation of the axon itself
• Microtubules run parallel to the axis of the of
the axon
• Structural integrity
• Transport of proteins from the cell body to the axon
terminal
• Polymerization and depolymerization is regulated by
several proteins

synaptogenesis

Once an axon reaches its target region, additional cell-cell
interactions dictate which target cells to innervate from
among a variety of potential synaptic partners.
Synaptogenesis

Once synaptic contacts are established, neurons become
dependent on the presence of their targets for continued
survival as well as further growth and differentiation of
axons and dendrites.

Trophic interaction – long term dependency
between neurons and their targets
• Neurotrophic factors or neurotrophins
• Secreted by target cells
• Without trophic factors the neuron will die or undergo
apoptosis
• During development, a surplus of cells are produced

convergence and divergence

Convergence – the number of inputs to a target cell
• Divergence – the number of connections made by a
neuron
• Neurotrophic interactions regulate convergence and
divergence; this is also influenced by the size and
shape of neurons, particularly the dendrites