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Week 9 - Neural Development

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PSYC 4010
Scott Adler

Neural Development - Between 10 and 20 billion neurons in the adult cortex - Between 50 and 200 billion glial (support) cells - Neocortex: speed up or slow down specific signals, they can inhibit certain neurons based on info they are getting - Great diversity in shape, form, and interconnections of neurons - Goal of studying development o How diversity is achieved o How each portion and structure of CNS is integrated into a whole to allow coherent functioning Brain Area - Brain Stem o Role in basic attention, arousal, and consciousness o All info to and from our body passes through the brain stem on the way to or from the brain o Control very basic primitive behaviours in us - Cerebellum o Involved in the coordination of voluntary motor movement, balance, and equilibrium and muscle tone o Mainly involved in motor control o Possibly involved in working memory - Occipital lobe o The center of our visual perception - Temporal lobe o Involved in primary organization of sensory input o Our visual system breaks down visual info down into its component features o Later this info is put back together through temporal lobe where it can code and process whole object o Language is also a function, especially in terms of verbal labels for sensory info o Recognition of the “car” occurs in temporal lobe, application of the verbal label occur in conjunction of the recognition of the object o Visually recognize an object and be able to label it goes hand in hand o The temporal lobes are highly associated with memory skills - Parietal lobe o Can be divided into 2 functional regions  1 function integrates sensory info to form a single perception (cognition)  Synchronize that info and connect it as coming from the same event (visual info of the ball bouncing and the sound the ball hits will be integrated as a single perception of a single event rather than being 2 distinct events)  2 function constructs a spatial coordinate system to represent the world around us  Create a spatial map of our world (where things are in their world) - Frontal lobe o Involved in higher order cognitive abilities o Reasoning and decision making o Also responsible for planning (planning for behaviour) o Pre-frontal area = involved in working memory and decision making o The last area of the brain to have evolved and to be fully matured developmentally o A very slow developing system Assembly of Brain - Genome is the blueprint for the brain o Genome = our genetic material - Neurons and glial cells are the wiring for this (the foundation) - Axons, dendrites and synapses are the wiring for electricity of the brain o Info transmission is done through electricity of input/out from one system to the next o Put electrodes in the head and record brain activity o As you send signals through the brain, it creates electrical field that can be recorded - In terms of development, need to know when, where, and what things develop When - Most postnatal brain growth occurs within 3-4 years of life (measure the size of the brain) o But changes in myelination (rubber around the wire, electric signal will bleed out without the rubber. Electricity won’t travel through the end, the signal will slow down. Put this rubber covering which insulates it which allow speedy efficient signal down the sire)occurs well into aging, as late as 70-80 yrs o Myelination = fatty substance that wraps around the axons, allow faster signals down the wire o Problems in myelination cause autism, Parkinson’s Disease - Do things occur sequentially or simultaneously? o Neurons growing, myelination occurring, axons developing - In terms of differentiation of the diff areas of the brain, this occurs in the fetus - Early in the fetus, the brain is fairly smooth, but by birth much of the convolutions and invaginations occurred o 8 months: distinct physiological landmarks are there by the time we are born o Differentiation of the brain occurs very early on by 7-11 weeks - After birth, myelination begins and continues for many years - Further development of diff brain areas continue in an inside-out fashion (subcortical  cortical) o Teenagers don’t have the same decision making ability that in an adult has (not with experience, but because their brain is not equipped yet to make that type of decision, it hasn’t fully matured) o People who have problems (abused/addicted to drugs) their dev of brain becomes stunted/stopped o During birth process, serotonin rises. After birth, serotonin level drops  That drop signals various areas of the brain to increase development Where - Developmental subdivisions precede functional subdivisions - The various dimensions and divisions of the CNS are defined in the neural tube o Development of neural tube cavity becomes ventricles of the brain and canal of the cord o The top part of the tube eventually develops into the brain, the hollow parts become the ventricles o Development of neural tube wall provides an early organization of the CNS o Neurulation (week 3-4) – initial critical part of brain development Differentiation of Neural Tube - Bottom 50% becomes spinal cord - Intermediate part becomes the brain stem (medulla, pons) - Top part becomes the brain o Disproportionate growth of top part of tube is called encephalization o Differentiates into 3 vesicles The Vesicles - Prosencephalon (forebrain) o Divides into the telecephalon (cortex) and diencephalon (thalamus and hypothalamus) - Mesencephalon (midbrain) - Rhomencephalon (hindbrain) o Further divides into metencephalon (pons and cerebellum) and myelencephalon (medulla) - Continuing division o Starts with neural tube – top of the neural tube forms the brain o Inside the cavity of the tube differentiating into 3 parts o 3 vesicles into 3 portions of the brain What - Cell proliferation - Cell migration = cells moving from where they were initially formed to where they need to be in the brain - Cell differentiation - Cell death = getting rid of cells that you don’t need or use - It is a process: proliferation  migration  differentiation  death o A time line is sequential o While there are cells migrating, there will be cells proliferating as well Cell Proliferation - By the end of infancy, the volume of neurons has increased significantly o 1000 per cubic milometer in newborn o 450% increase in number of neurons by the end of infancy o In childhood, you start getting rid of neurons o In teens, volume of neurons stabilizes (not the amount of neurons, the volume/space neurons take up!!) - Density, however has decreased o Volume is increasing, but density is decreasing due to differentiation o Initially neurons is just a cell body, there are not dendrites/axons when they first form, just the cell o In prenatal period, you make lots of neurons o Then once you are born, you lose neurons (density decreases) these neurons are building synapses and dendrites. It is taking up more space o More synaptic connections you make, more axons/dendrites  the more volume Cell Migration - Passive cell displacement o New cells push old cells outward  go to their functional areas or division of brain where they are supposed to be o Proliferative zone: produces cells, new cells push old cells producing layers of cells (layer 1 is produced before layer 2, layer 3 pushes layer 2) o It is passive, cell is not doing the migrating – it is being pushed there o Short distances – cells don’t go very far from the proliferative zone o Out-inside spatiotemporal organization  Older cells are further out, younger cells are further in - Active neuronal migration o Long distances – cells produced in proliferative zone and moves far from it o Inside-outside spatiotemporal organization
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