Chapter 13: Neural Development and Developmental
Embryonic life 3 weeks after conception
Neural plate forms from the ectoderm of the embryo it's a patch of cells on the dorsal
surface of the embryo which eventually becomes the nervous system
Cells in the neural plate are stem cells they are pluripotent meaning they have the
potential to develop into different types of nervous system cells
Neural plate starts to form a groove day 24 fuses to form the neural tube.
Proliferation: Cells of the neural within ventricular zone starts dividing.
Next, 3 bumos form on the anterior portion of the neural tube eventually forming the
forebrain, midbrain, and hindbrain of the CNS.
Cells start migrating following glia & once neurons migrate, they begin to grow axons
& dendrites and differentiate into their final forms.
Cell differentiation is essentially complete at birth.
Problems with any phase of development can lead to significant abnormalities in the
Brain is extrememly vulnerable during last 4 5 months but failures at any point can
have a significant impact on the final form of the brain.
Problems: can originate within neurons themselves, genetic/chromosomal abnormalities,
or external factors.
One common malformation = when neural tube fails to close or incomplete closure.
Craniorachischisis: complete failure of the closure of the neural tube fatal
Spina bifida: complete neural tube closure failure different subtypes mostly
results in neurological difficulties that are associated with locomotion rather than
cognitive difficulties syndrome has its primary effects on the spinal cord.
Anencephaly: partial closure of the neural tube generally fatal.
Most neurons have migrated & have differentiated into their final forms but just the
beginning of a long period of brain growth and change.
Synaptogenesis & Dendritic Branching
Neurons undergo long period of synaptogenesis & dendritic branching producing
far more synapses & dendrites that are needed.
Both continue to occur even after birth and sometimes well into adulthood.
With time, dendrites become more complex.
Birth to 2 yrs synapse formation enters a period of rapid growth.
Soon after period of synapse reduction neural death is apoptic
planned/programmed cell death critical feature of development.
Synapses that do not make functional connections or that make incorrect
connections are especially likely to die, leaving room for other synapses to sprout.
Emergence of behaviours such as sitiing, walking, or speaking correlated with extensive
growth in cortical areas of the brain, which increases its volume by 4 times btwn birth &
One way to study this relationship is to study the maturation of specific parts of the brain &
observe whether or not certain behaviours become evident only when the brain reaches a
certain level of maturation.
CNS and the Environment
Env't plays a huge role in CNS development. Plastic Change & Critical Periods
Plastic change: the abilitiy of the CNS to alter itself in response to environmental
Critical Periods: There are critical periods of plastic change in which the environment
can have a maximal effect on CNS.
Duration and timing of these critical periods vary by species, but seems like human
exhibit prolonged periods that often occur later in life after prenatal period.
Shaping of the CNS during critical periods does not depend on random events in the
Plasticity occurs in response to specific experiences:
Experience expectant plastictic changes
Those CNS changes that are dependent on experience(s) during the critical
period for specific synapses to develop as they should.
Sensory cortex has these experience expectant critical periods
Organism must experience sensory stimulation during the critical period to
develop normally otherwise, sensory impairment.
Idiosyncratic experiences that occur during critical periods that also affect brain
Musical training in childhood has an affect on the increase in size of the
auditory cortex later on in life.
Until 4 yrs of age, cortical gray matter volumes increase
Synaptogenesis and dendritic branching occur both prenatally & postnatally and are
maximal during critical periods.
Brain's ability to engage in plastic change is often reduced as we age, especially once the
critical period has passed except for plastic changes related to learning which occurs
Although the factors underlying plastic change are not completely understood, it appears
that neurotrophins (chemicals of neurons) and neurotransmitters play critical roles.
Hypothesis that complex behaviours are associated with the myelination of cortical areas
sensory and motor areas myelinate early on, therefore sensory and motor behaviours
seem to emerge first.
Parietal Lobe Development
In comparison to the other lobes of the brain, relatively little is known about the
development of parietal lobes.
Inconsistent levels of development at birth; some parts of the parietal lobe are more
mature than others.
Babies 2-3 months large increases in glucose utilization in parietal lobes remain
steady until about 2 to 3 yrs of age.
Children under age 6 often unable to name or point to a finger that was just touched
when they canot see their hands so although they can perceive touch, they have hard
time localizing the point on their hands.
8-12 yrs adultlike levels of performance
Parietal lobe is also a component of the dorsal visual stream visual stream involved in
processing of spatial information & directing behaviours toward certain points in space
& processing motion.
To understand the mechanisms underlying the development of parietal lobes look at
mild to moderate cognitive impairments
sparing of verbal ability, frontal & temporal loves
difficulties with tasks of visuospatial ability
smaller brain volumes but reduction in brain size is not uniform throughout the CNS
disproportionate reductions in parietal & occipital lobes. May be a result of missing gene on chromosome 7
Therefore, genes on chromosome 7 may underlie typical development of parietal,
occipital and/or white matter in the CNS.
Occipital Lobe Development
Development of occipital lobe is incomplete at birth.
Newborns do not actually have underdeveloped visual systems it's quite sophisticated
actually capable of distinguishing btwn 2D and 3D stimuli. Also have form perception.
Become competent with complex stimuli such as faces quickly.
3 months optic tract and optic radiations become heavily myelinated resembling
6 weeks emergence of binocular vision
Development of the visual cortex is critically dependent on the environmental
experiences of the individual.
Stabismus: Eyes are misaligned problems with depth perception
Those who get treatment for this after critical period often continue to have impaired
Critical period for binocular vision - 1 few months of life 1-3 yrs.
More complex visual tasks longer to develop.
Simple face & emotion recognition is performed at adult levels by children btwn the
ages of 6 and 8 yrs.
Complex tasks requiring participation of the frontal lobes may not develop until the
Temporal Lobe Development
Develompment of temporal love appears to depemd on the specific structures and the
function that is being studied.
Development of speech production and comprehension is the result of the cooperation
and development of the frontal and temporal lobes
Develompment of linguistic competence involv