NEURO Epilepsy + neuroplasticity Flashcards
(15 cards)
What happens to the zygote after fertilisation? (phases of neurodevelopment).
Zygote begins to divide.
What happens on day 4 of phases of neurodevelopment?
solid ball of cells called morula forms, made of 26 cells.
What happens on day 5 of phases of neurodevelopment?
Cells in two groups
Inner cell mass= embryo. This inner layer eventually separates into 2. Epiblast (embryo) and hypoblast (part of gut).
Encompassing sac (placenta)- includes cells secreting fluid creating cavity= blastocyst.
What happens on day 13-19 of neurodevelopment?
‘gastrulation’. Formation of a groove- the ‘primitive streak’.
Results in production of 3 cell layers.
-Ectoderm: nervous system develops from this.
-Mesoderm:: middle layer of three germ layers.
-Endoderm: forms internal organs.
In front of primitive streak, ectoderm thickens to become ‘neuroectoderm’, forms the ‘neural plate’.
What happens on day 20 of neurodevelopment?
Uneven rates of cell division form a grove- ‘neural groove’- becomes midline of the embryo. Ridges of ectoderm bulge on each side of midline, meet in middle to become ‘neural tube’.
Interior become fluid filled ventricle of brain and central canal of spinal cord= neurula.
What happens on day 24 of neurodevelopment?
3 major divisions of brain identifiable.
-prosencephalon (telencephalon + diencephalon)
-mesenchephalon
-rhombencephalon (metencephalon + myelencephalon).
How does fluid filled tube of cells develop into the brain?
- channel between spinal cord + brain partially close.
- fluid pumped into swell the brain.
- differential rates of cell growth determine region of enlargement.
- regions of swelling demarcate future brain regions.
- 3-4 weeks tube doesn’t remain in straight line.
- telencephalic tube grows over the rest of the brain to form the cerebral cortex.
- forms occipital and temporal lobes + takes fluid- filled core with it.
- expansion by 6 months (foetus); early- stage sulci and gyri or the cerebral cortex.
- 9 months foetus brain is like adult brain.
Where do neurons come from?
During fastrulation, cells in ectoderm around midline receive chemical sign from notochord. Causes development into neural precursor cells.
Neural stem cells- divide (hallmark of stem cells).
Once divided they produce a primitive neuro (neuroblast) or glial cell (glioblast) and another precursor.
These cells migrate along tubes ventricular zone until find out where meant to be. Migration with gui-dance mechanisms.
Once in position have to decide what neuron type want to be. Determined by local chemical interactions with neighbouring cells.
Neurons need to change shape + interconnect to form neuronal circuits. Initially produce several small extensions, but then commit to one of these being the axon and other dendrites.
Axons used growth cones (specialised terminals) to find targets. Growth cones consist of lamellipodia (sheet- like expansions) and filopodia (fine processes). Receptors in filopodia sense attract of repellent chemical cues in environment.
How do axonal growth cones navigate?
Use diffusible agemts:
-chemoattractant.
-chemorepellents.
Non-diffusible agents: sit in tissue that the axon is crawling in.
-contact attractants.
-contact repellents.
(get pushed away by one and attracted by the other, these determine where the axon is going to go).
How many of the neurons composing the adult brain have been created by the 7th pre-natal month?
Majority. Volume of human brain quadruples birth-> adulthood. Cause of synaptogenesis myelination, dendritic branching.
Postnatal growth not set in stone- can be influenced by experience cause brain is plastic. E.g. Postnatal hydrocephalus (build up of spinal fluid in brain) can have massive changes in brain after birth + still be fine.
How does life experience effect the brain?
Can influence the postnatal wiring of the brain. Can get lots of information from study of visual system in ‘visual’ animals (monkeys and cats). Easy to deprive or augment visual experience.
How does vision work in the brain?
Info from 2 eyes passes through dorsal lateral geniculate nucleus to primary visual cortex. (V1).
Left + right primary visual cortex receives information from both eyes.
How can vision be used as an example of early development of the brain?
Early closure of one eye effects distribution of cortical neurons driven by stimulation of both eyes (cats).
Look at how many neurons activated when light shone into cats eyes.
When no visual input for 2 + 1/2 months means eyes wired when it opens visual fields not used even when light shone in both eyes.
Cat critical period= 3 months, monkeys= 3 months.
Monocular deprivation in critical period affects axonal branching in visual cortex (cats).
What are some examples of neurodevelopment being important in adults too?
+London taxi drivers have bigger (posterior) hippocampi.
+ Visual cortex responds to Braille in late- blind individuals.
(Complete blindness post-puberty- due to glaucoma, PET using H2015. Reading Braille leads to activity in visual cortex).
What are the mechanisms for adult neural development?
-Axonal sprouting: cats with retinal lesions. Injected tracer at edge of ‘blind cortex’. Fibres projecting into blind areas had more elaborate arbous.
-Adult neurogenesis: now know new neurons (and glial cells) generated reliability into regions of adult brain. Olfactory bulb, hippocampus and although area adjacent to lateral provides neuroblasts that later form neurons in olfactory bulb.
In hippocampus produced in dentate gyrus called the ‘sub granular zone’. Become integrated into synaptic circuits.
