development Flashcards
8 steps of nervous system development (steps are actually integrated)
- neural induction
- neurulation
- morphogenesis & patterning of neural tube
- neurogenesis
- neuronal migration
- axon growth & pathfinding, dendritic arborization
- synaptogenesis
- gliogenesis (myelination)
neural induction steps
neural plate forms from the dorsal ectoderm
Epidermal fate is signalled by BMP (bone morphogenic protein)
Neural fate is induced by blocking of BMP signal, which is done by the “organiser” region (the node) using Noggin (Ng) or Chordin (Chd)
neurulation steps (formation of neural tube)
- elevation of neural folds
- fusion of neural folds in dorsal midline (zips up bidirectionally from points of closure)
- pinched off from epidermis, cells at the ends differentiate into neural crest cells & migrate away
** neural plate cells express self adhesion molecules to allow for recognition & fusion
defects caused by failure of neural tube closure
spina bifida (caudal), anencephaly (cranial)
fate of neural crest cells
Give rise to peripheral & enteric ganglia, melanocytes (pigment of skin & eyes), Schwann cells, cartilage & bone of face & jaw
initial patterning of neural tube
Wall of neural tube = neuroepithelium, fluid-filled central cavity = ventricular system
Three distinct vesicles form from this:
At rostral end (brain), prosencephalon (forebrain), then mesencephalon (midbrain) then rhombencephalon (hindbrain), then spinal cord
further segmentation/patterning of neural tube
prosencephalon -> telencephalon & diencephalon
rhombencephalon -> metencephalon & myelencephalon
overall (rostral end to spinal cord end):
telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon then spinal cord
fate of the 5 vesicles in the morphogenesis stage
- telencephalon: olfactory bulb, cerebral cortex, hippocampus, striatum/basal ganglia
- diencephalon: thalamus, hypothalamus, retina of the eye
- mesencephalon: midbrain
- metencephalon: pons (in brainstem), cerebellum
- myelencephalon: medulla
how does patterning of neural tube occur (cell fate)
Ectoderm induces roof plate, secretes dorsalizing morphogens (BMPs, FGF, Wnts). Specifies interneuron type
Notochord induces floor plate, secretes ventralizing morphoen (Sonic hedgehog). Specifies motorneuron type
** gradients of these signals (strong closer to each plate) provide variety of positional cues
neurogenesis steps
Neuroepithelial cells differentiate into multipotent radial glia (radial glia are NOT glial cells), which the divide symmetrically or asymmetrically to produce neurons & glial cells.
Symmetrical at the start to produce large pool, then asymmetric, then symmetric at the end producing two differentiated cells.
Cortical layer is formed inside-out. Cajal-retzius cells of MZ secrete attraction factors so new cells migrate to under pial surface.
Radial glia body is on ventricular surface but provide scaffold up to pial surface for migration of neurons.
order of neuro/glio genesis
Neurogenesis occurs BEFORE gliogenesis (each process inhibits the other so they arent concurrent)
pyramidal neurons properties
Excitatory long range projection neurons (to other cortical hemisphere or other targets outside of cortex eg spinal cord)
~80% of neurons in mature cortex
interneurons properties & production location
Locally projecting, inhibitory neurons that modulate excitatory output of pyramidal neurons
~20% of neurons in mature cortex
Cortical interneurons are produced in the basal forebrain & migrate
growth & branching of neurons
Influenced by environmental factors:
Local signals (contact dependent or diffusible) and active synapses
Tip of growing axon = growth cone
Actin filaments regulate shape & growth
Microtubules provide structural support (essential for extension)
how do excitatory & inhibitory synapse densities in the prefrontal cortex change after birth
excitatory: dramatically decreases
Inhibitory: increases
