W1 Neurodevelopment Flashcards
Morulation
= 1st step of nervous system formation (day 4), solid ball of cells, morula forms.
Blastulation
(day 5) Cells separate into 2 groups:
1- Inner cells mass (will form 2 layers = Epiblast (embryo) + Hypoblast
2- Encompassing sac (trophoblast will form the placenta these cells secrete fluid creating a cavity)
Gastrulation (basic)
(day 13-19) Formation of a groove ‘primitive streak’ ( a dip)
3 layers = Ectoderm (forms neuroectoderm), Mesoderm (bones, muscles, connective tissues),
Endoderm (digestive system, lung, liver)
Day 20: Neuronal plate development
(day 20) Neural plate forms neural groove, meet up and create a neural tube and central canal (day 22). Ridges of ectoderm bulge on either side of the midline.
Day 22 (3 weeks) Neuronal tube
(22 days, 3 weeks) Neural tube forms, interior becomes the fluid filled ventricles of the brain and the central canal of the spinal cord = neurula (neurulation).
Day 24: Major divisions
(day 24, within week 3): 3 basic divisions = Prosencephalon (telencephalon and diencephalon), Mesencephalon, and Rhombencephalon (metencephalon and myelencephalon).
How does the neuronal tube become a brain?
Channel between spinal cord and brain partially closes.
Fluid is pumped in to swell the brain.
Differential rates of cell growth determine regions of enlargement.
Regions of swelling determine future brain regions
Optical vesicle
= structure of the eye, will become retina. (starts as part of the NS)
3-4 weeks (1st curve)
1st bend, tube curves over (cephalic flexure)
5 weeks
5 weeks: primitive spinal cord and brain form next bend.
Telencephalic tubes grows over the rest of the brain to form the cerebral cortex. As it travels it forms the occipital and temporal lobes, fluid-filled core becomes the ventricles.
6 months = feotus
Early stage sulci and guri of th ecerebral cortex. Landmarks start to appear.
9 months
Brain is fully formed.
Gastrulation (notochord)
Cells in the ectoderm around midline receive a chemical signal (e.g. nogging). Notochord produces chemicals, encourage the cells to think of what to do.
Notochord causes some of them to develop into neural precursor cells, neural stem cells divide, proliferation (symmetrical)
Neuroblast and Glioblast
Precursors produce a primitive neuron and glial cells which are neuro/glioblasts
Migration
eurons/glia cells are produced in the tube’s ventricular zone. Neuroblasts/glioblast migrate to their final destination (chemical expressional in the tissue.
Radial glial cell body: enormous procedure goas up to the pial surface, cells move up this.
What will these cells become (post-migration)
Once they reach their target, they need to decide what type of neuron (or glial cell) they want to be. Neural stem cells form neural progenitor and glial progenitor will become either neuron, astrocyte, oligodendrocyte. Local chemical interactions determine what type of glial cells/neurons they become.
How do axonal growth cones navigate ?
Diffusible agents = Chemoattractants + Chemorepellants.
Non-diffusible agents (molecules stuck to the membrane, the growth cone is crawling): Contact attractants + contact repellents
Neuronal development: interconnect circuits
Immature neurons initially produce a number of small extension (neurites). Eventually commits to one of these being the axon and the other dendrites (multipolar stage). One the axon has been specified it navigates to find its target (the dendrites are similar).
Dendritic branching
Dendrite change
What are growth cones?
Growth cones consist of lamellipodia (sheet-like expansion) and filopodia (fine processes): chemical sensors (contained) = senses attractant or repellent chemicals which tells them where it needs to be.
Synaptogenesis
formation of synapse
Dendritic branching
Dendrite change
What happens to the visual cortex when you become blind post puberty?
Study found was when people read Braille the visual cortex activated, instead of activating from visual inputs it was from a tactile information. (PET using H2O15). Reading Braille leads to activity in the primary visual cortex (amongst other areas).
Neuroplasticity mechanisms (1): Axonal sprouting
Axon is not static they can sometimes change and invade certain tissue that is vacuum, injected tracer the axons going into the blind bit were larger, almost like the brain realized the tissue wasn’t being used. Cats with retinal lesions killed 8.5 months post-lesion. Injected tracer at the edge of the ‘blind cortex’. Fiber’s projecting into the blind area had more elaborate arbors.
Adult neurogenesis
2 areas of the brain that can produce new neurons as adults:
Hippocampus = (olfactory bulb (smell) neurons), close to the ventricles.
Hippocampus = produce new neurons into the tissue, comes from the sub granular zone = one local area.
In the hippocampus, produced in area of the dentate gyrus called the ‘sub-granular zone’. Become integrated into synaptic circuits. Newly generated granule cells contacted by GABAergic synapses in the granule cell layer (hippocampus)
When was the mahority of neurons that compose the adults brain created? And how come the brain x4 between brith-adulthood?
By the 7th pre-natal months. Because of Synaptogenesis + Myelination + Dendritic branching.
Main visual pathway in humans
‘geniculostriate system’. Information from the two eyes passes through the dorsal lateral geniculate nucleus to the primary visual cortex (V1). The left and right primary visual cortex receives information from both eyes.
How do carnivores and apes input visual information?
inputs carrying information from the two eyes from an alternating series of eye-specific domains in the primary visual cortex.
How does closing/not using one eye during development affect the development of the visual system in animals?
There is an effect of early closure of one eye (during development post-birth, critical period (3months for cats)) on the distribution of cortical neurons driven by stimulation of both eyes is the The imputs of the brain die away, it is eversible.
Monkey Monocular deprivation
Monocular deprivation affects the width of ocular dominance columns in the visual cortex. Monkeys (2weeks to 18 months) in normal same width very different to monocularly deprived. Monkey’s critical period is 6 months.
Axonal brancing in the visual cortex: cats
Axon increases in the eye that is open. Expends in deprived cortex, tissue not used, lets expend our inputs. Short term deprivation impact in thalamus = big axons armers, branches that normally wouldn’t be there. Deprived eye = nothing there, just simple axon inputs. Long term or short-term same effects as long as it is in the critical period.
Brain is adaptable: example of brain plasticity
weakness in a leg, noticed his intra-cranium spce full of fluid. Postnatal hydrocephalus. Blocked the fourht ventricle so the CSF cannot flow out of it, puts pressure on the tissue however he was perfectly normal.
Postnatal hydrocephalus
Condition increase fluid pressure as result of blockage.
Stem cells
unlimited capacity of self-renewal due to asymmetric cell division, ability of each stem cell to develop into many different kinds of cells.
Neural proliferation
After the neural plate is formed, cells of the tube begin to proliferate (increase), not simultaneous or equal in all parts of the tube. Most cell division occurs in the ventricular and subventricular zone (adjacent to ventricles).
What are the key mechanismes in neural proliferation
controlled by chemical signals from two organizer areas in the neural tube = Floor plate (along midline of ventral surface of tube) and the Roof plate (runs along midline of dorsal surface).
Radial migration
proceeds from the ventricular zone in a straight line towards the outer wall of the tube.
Tangential migration
occurs at a right angle to radial migration.
Somal translocation (migration)
process that extends from its cell body, explore the immediate environment with chemicals guiding the movement (repelling, attracting), the cells move in either tangential or radial fashion.
Radial-glia-mediated migration
long process extends from each radial-glia cell as a sort of rope to pull itself up and away, only migrate in a radial fashion.
Aggregation
Developing neurons align with other developing neurons, after migrating.
What are the three non-eclusive mechanism of Aggregation?
Cell-adhesion molecules (CAMs); located at the surface of neurons, recognise molecules on other cells and adhere to them.
Gap junctions; communicate between adjacent cells, bridge by narrow tubes (connexins). Interactions between glial cells and neurons
Active cell death
apoptosis
Passive cell death
necrosis
Critical periods of development
interval that is key in influencing development iwth a need for expeirence to occur.
Sensitive period of development.
the period where an expeirence had a great effect on development when it occurs but can still have a week effects outside of the period.
