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Human Brain - Chapter 13.docx

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Ted Petit

Chapter 13 – Neural Development and Developmental Disorders - beh changes often correspond with periods of brain growth/reorganization MODULE: Neural Development Early Development - early in embryonic life [3 weeks] the neural plate forms from the ectoderm of the embryo - neural plate > is a patch of cells that are on the dorsal surface of the embryo o eventually becomes the nervous system - cells of the dorsal ectoderm in the neural plate are stem cells that are pluripotent, meaning that they have the potential to develop into diff types of nervous system cells [cannot turn into an other type of cell] - then the neural plate starts to form a groove which by embryonic day 24 > fuses to form the neural tube [diff sections of the tbe become diff parts of the neural tube] - interior surface becomes the ventricles and central canal of the spinal cord - 3-5mnths of gestation > proliferation – the cells of the neural tube within the ventricular zone are rapidly dividing - by day 40 > 3 bmps that eventuall form > forebrain, midbrain, hindbrain of CNS - cells also migrate from the interior ventricular zone to their final location by fndlowing certain types of glia - 2 month > telencephalon undergoes tremendous growth > developing the cortical plate [as migration occurs > deepest layers of neuron develop first] - once the neurons migrate the being to grow axons/dendrites and begin to differentiate into their final form o must get to their approp target and make functional synaptic connect o axons and dendrites follow chemicals > arranging themselves in a orderly fashion in a position relative to their initial place - cell differentiation is essentially complete at birth - the brain is particularly vulnerable during the last 4-5mnths of gestation - problems at an stage can cause sign impact on the final form of the brain - the type of CNS malformation can tell us something about when it occurred - crainorachischisis > a fatal defect of the neural tube that results when there is a complete failure of the closure of the neural tube. the CNS appears as a groove in the top of the head and body - spina bifida >a neural tube defect that is characterized by spinal cord defects; not necessarily fatal though it can vary in its severity o diff associated w/ locomotion rather than cogn - Anencephaly > generally fatal failure of the rostral part of the neural plate to fuse; characterized by a general absence of the cerebral hemispheres - 7mth > neurons migrated and differentiated into final forms - synpatogenesis > production of synapses - dendritic branching > branching of dendrites that can result in increased number of synapses [more than needed in the adult brain] [slowly > spines] o neurons undergo a long period of the above 2 o both occur after birth and sometimes into adulthood - synaptogenesis > sparse during embryonic life, before birth>2yrs rapid grwt o followed by a period of synaptic reduction > max rate – puberty - 50% more neurons are developed in the developing brain than needed in the adult brain [death is a normal and critical feature of development] - much of the death is apoptotic > programmed cell death > not sure of trigger - apoptosis > controlled by genes - synapses that don’t make functional connections or incorrect connections are more likely to die > leaving room for new o these apoptotic changes occur after birth and may have to do with enviro and experiences of the individ Postnatal Development - cortical area increases by 4 times btwn birth and adulthood - plastic change > is the ability of the CNS to change itself in response to environmental stimuli - critical periods > of plastic change in which the environment can have a maximal effect on the CNS [longer lived species > prolonged CP that occr late] - plasticity during CPs occurs in response to specific experiences - experience-expectant plastic change> CNS changes that are dependent on experiences durin the CP for specific synapses to develop as they should o sensory cortex [stim. after cp limited effect, during long lasting] - experience-dependent plastic chane> idiosyncratic experiences that occur during CPs that also affect brain development o musical training b4 age 9 > increasing size of auditory cortex o increase was proportional to the age started/change in random area - volumes of cortical gre matter increase until about 4yrs > synatogenesis, dendritic branching [both occur pre/postnatal], myelinatio of axons - ability for plastic change reduce as we age > some exceptions [ability to learn - neurotrophins > chemicals, such as nerve growth factor, that are secreted by the brain that enhance the survival of neurons - neurotrophins and neurotransmitters seem to play a role in plastic change - white matter volunes increases steadily until about 20 years fo age - much of cortex is not myelinated at birth > does not occur uniformly in corte - has been proposed that myelination corresponds with the emergence of beh Parietal Lobe Development - relatively little is known about the development of the parietal lobes - inconsistent levels of development [some parts more mature than others] - tactile reflexes > somatosensory systems may be functional at birth - myelinatoin of the spinal cord occurs prenatally and complete around age 1 - increase in glucose utilization 2mnts -2/3yrs > improvements in visuospatial and visuosensorimotor skill - although basic tactile sensation mature early, complex tactile discriminations require more time to develop - dorsal visual stream > processing of motion - Williams Syndrome > genetic condition in which some of chromsome 7 is deleted > sparing f verbal ability and significant diff w/ visouspatial ability o disproportionate reduction of parietal and occipital lobes  chromosome 7 could underlie typical development of parietal Occipital Lobe Development - development is incomplete at birth - can distinguish 2D/3D, rudimentary form perception - competence with visual stimuli > myelination of the optic tract and require the optic radiations to become functionally connected with the sensory organs and with other areas of the brain [by 3mnth myelination near adult] - 6 weeks begin to experience binocular vision > stable around 6 mths - development of the visual cortex is critically dependent on the enviro exp - amblyopia > a decrease in vision in one eye, lazy eye - strabismus >misalignment of the ees in which one or both eye deviate towards the nose - if problem occurs during the CP then worst - although basic visual functions may be present relatively early, more complex tasks requiring the participation of the frontal lobes may not develop until the teens Temporal Lobe Development - to understand development divide into two type: linguistic and hippocampally dependent memory function - linguistic ability > multifaceted > cooperation of frontal and temporal lobes - although auditory cortex presumed functional at birth it may not make functional connection w/ other important language areas [brocas/wecknick] - between ages of 1-2 number of important commissural systems are undergoing myelination > critical period for language - failure to experience linguistic stimulation during this time can result in permanent deficits in attaining adultlike linguistic skill - 2-12rys changes in dendritic arborization occur in speech areas of the brain o lanaguage development > sensitive to environmental factors - the correlation between neural maturation and linguistic ability ma reflect idiosyncratic patterns of maturation of the speech areas that ma have a large environmental component - hippocampus > adult volumes > 7-10 mnths of age o high level of glucose utilization > unlike the rest of the temporal structures that which show relatively low levels of glucose utilization until about the age of 4 o hippocampally dependent memory function are not mature at birth o exhibits neurogenesis in adulthood [memory func ma be due to its ability to extend its developmental period throughout the lifetime] o memory func rely on functional connection w/ the parietal and frontal  develop over the 5-7yrs of life [although at birth may seem that things are present takes time to be full functional] o most people exhibit childhood amnesia for events that occurred before the age of 3/4 suggesting that the CAN systems for encoding, storing, retrieval of memories are not yet functional - autobiographical memories subserved in many diverse areas of the brain - frontal lobaes are among the last to mature [up til for 4yrs consistent with the time frame of autobiographical memories being to develop] - many developmental features of memory are associated with development of the temporal lobe and with increase in connectivity among cortical areas Frontal Lobe Devleopment - prefrontal cortex is the least developed at birth reaching adult level of myelination, glucose utilization and cell differentiation in the middle teens to late teens Motor function - motor areas > rapid development > sign maturation by 3 mnths of age - generally > parts of the frontal lobe assoc with later developing traits take longer to develop > those involved in basic functions develop more quickly - prediciable milestones > o head > arms/trunk > legs o cephalocaudal – development of motor functions in which the head and the trunk and controlled before the legs are o proximodistal > dev of motor skills that occur in the head, trunk and arms before occurring in the hands and fingers - gross motor skills > motor skills that involve the large muscles that are typically involved in walking, balance or holding up the head [develop first] - fine motor skills > involve small muscles and are typically used in the coordination of the hands and fingers [develop after] - birth > motor roots are highly myleinated / 6mths > subcoritcal motor areas are at least moderately myelinated - 3mnths > secondary/tertiary motor areas of the frontal lobe show differentiated neurons and adult type inhibition - thus, although myelinatoin fo these tracts begins early > diff and maturation of these areas extend well into early childhood o may implicate frontal lobe develop in > motor beh that appear childho - other factors also play into the motor development other than myelination - Rett Syndrome > occurs in 3/4 mnths after birth > gene mutation, MECP2 > begins to arrest brain development o by the end of the 6-18mnths > hypotonia, loss of the use of hands, apraxia > not myelination loss but dendritic aborization in motor coritices is reduced o also numerous alteration in neurotransmitters in affected areas - normal motor development rely on > postnatal differentiation of neurons, synaptogenesis, dendritic arborization, neurotransmittion, myelination Executive Function -
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