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Chapter 13

PSYB65 Chapter 13.docx

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Ted Petit

Chapter 13: Neural Development and Developmental Disorders  Neural Development Early Development • Neural plate forms from the ectoderm of the embryo o Neural plate is a patch of cells that are on the dorsal surface of the embryo and eventually becomes the nervous system o Cells of dorsal ectoderm are stem cells that are pluripotent (can develop into different types of nervous system cells) o Neural plate forms groove and forms neural tube o Cells of neural tube rapidly dividing called proliferation  Bumps eventually form parts of the brain of the CNS • Craniorachischisis o Complete failure of the closure of the neural tube is fatal o Spina bifida and anencephaly result from partial closure of the neural tube o Anencephaly occurs when the rostral part of the neutral plate does not fuse  Generally fatal • 50% more neurons are produced in the developing brain than are required in the adult brain o Neural death is apoptotic, or planned, programmed cell death  Controlled by genes Postnatal Development • Plastic change is the ability of the CNS to alter itself in response to environmental stimuli o Critical periods of plastic change in which the environment can have a maximal effect on the CNS  Duration and timing of this vary by species  Longer-lived animals (eg. humans) exhibit prolonged critical periods that often occur later in life  Experience-expectant plastic changes – those CNS changes that are dependent on experience(s) during the critical period for specific synapses to develop as they should • Much of the sensory cortex appears to have these  If an organism does not experience sensory stimulation during the critical period, long- lasting impairments in the sensory modality occur • Sensory impairments that occur after the critical period often have limited effects on the cortex o Experience-dependent plastic changes – idiosyncratic experiences that occur during critical periods that also affect brain development o Synaptogenesis and dendritic branching occur both prenatally and postnally and are presumably maximal during critical periods  EXCEPTIONS: • Plastic change required for learning extend well into adulthood • Neurotrophins play critical roles Parietal Lobe Development • Parietal lobe has inconsistent levels of development at birth • Williams syndrome o Mild to moderate cognitive impairments o Smaller brain volumes o Reduction in brain size is not uniform throughout the CNS o Relative sparing of the frontal and temporal lobes and disproportionate reductions in parietal and occipital lobes o Significant reductions in white matter o Missing genes on chromosome 7 that may underlie typical development of parietal occipital, and/or white matter in the CNS Occipital Lobe Development • Development of the occipital lobe is incomplete at birth • Newborns have sophisticated visual systems • Cataract is removed after critical period, normal eye has only poor visual acuity, exhibiting permanent amblyopia • Strabismus – when the eyes are misaligned o Impaired depth perception, loss of binocular cells in the visual cortex o Critical period ends sometime between 3-4 years of life Temporal Lobe Development • Between 1-2 years, important commissural systems are undergoing myelination o Corpus callosum, anterior commissure, and fornix • 2-12 years, marked changes in dendritic arborisation occur in speech areas in the brain o Environment can affect language development • Memory functions of hippocampus result from its ability to extend its developmental period throughout the life span o Develop over the course of the first 5-7 years in humans o Recall of autobiographical or episodic information does not appear until 4 years of age Frontal Lobe Development • Prefrontal cortex is least developed at birth o Adult levels in middle to late teen years • Motor development follows cephalocaudal and proximodistal patterns of development o Head is controlled before the arms and trunk are, bu
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