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PSYB65H3 Lecture Notes - Marasmus, Neuroglia, Chromosome

Course Code
Ted Petit

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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
- cells also migrate from the interior ventricular zone to their final location by
following certain types of glia
- 2nd 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