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Prenatal Development
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We have the gametes, eggs and sperm,
produced by meiosis and each with half of the
required genetic material (a single set of 23
chromosomes)
conception - egg and sperm come together to
produce a single cell or zygote that has all of
the genetic material (23 pairs of
chromosomes) and development begins
Stage 1: Zygote (Conception 2 weeks)
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Cells multiply by mitosis
Changes to hollow ball of cells, called a
blastoma
Implants in uterus
Cells begin to differentiate and
specialize into the cells that will be the
embryo and those that will support the
embryo (e.g. amniotic sac, umbilical
cord)
Stage 2: Embryo (3 - 8 weeks)
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All major internal and external
structures form
Three layers of cells
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Endodermal - internal organs
Ectodermal - nervous system, eyes, ears,
skin
Mesodermal - muscles, bones, heart
Major brain development in week 5
Neurulation (week 3-4)
Neural
Groove
Neural
Plate
Ectoderm
Surface
Ectoderm
Notocho rd
Neural
Groove
Ectoderm
Neural
Plate
Notocho rd
Neural
Tube
Neural
Crest
Notocho rd
Stage 2 (Cont.)
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Head is 50% of mass
Developmental Course
Stage 3: Fetus (9 - 38 weeks)
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Further development of body so
at birth head is only 25% of
mass
Stage 3 (Cont.)
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By 3 months, brain has differentiated
into visual, auditory, and cognitive
centers
All of the brain cells of the adult are
there by 3 months, but connections
among is not
In month 3, physical activity begins with
fist forming and toe wiggling
Stage 3 (Cont.)
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In month 4, eyes become sensitive to
light
In month 5, sounds result in activity,
including kicking and turning
Also may begin to show a sleep/activity
cycle
Stage 3 (Cont.)
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Later development includes progress in
the brain, lungs, development of fat that
allows at least some breathing, temp
regulation
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greater viability if premature
In month 8, immune system starts to
pick up with help from mom
Neural Development
Volume (mm3)
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By the end
of infancy
the volume
of neurons
has
increased
significantly
26 yr
13 yr
11 yr
5 yr
3.75 yr
19 mo
4 mo
2 mo
2 wk
6 days
Newborn
28 wk GA
0
1500
3000
4500
Neural Development
Neurons/mm3(x10 4)
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The
density,
however,
has
decreased
26 yr
13 yr
11 yr
5 yr
3.75 yr
19 mo
4 mo
2 mo
2 wk
6 days
Newborn
28 wk GA
0 10 20 30 40 50 60 70
Neural Development
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The number of
synapses, the
synaptic density,
and the number of
synapse per neuron
continue to increase
during the first year
and then steadily
decline
sy napse/mm3
total syna pse
7
6
5
4
3
2
1
0
28 wk 2 mo 8 mo
GA
2 yr
10 y r 70 y r
Neural Development
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The number of
synapses, the
synaptic density,
and the number of
synapse per neuron
continue to increase
during the first year
and then steadily
decline
sy napse/neuron
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
28 wk 2 mo 8 mo 2 yr 10 y r 70 y r
GA
Neural Development
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Stages:
Cell Production Fetus
Cell Migration - 7
mos.
Cell Elaboration
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Culling
Myelination - 4 yrs.
Quic kTime™ and a
GIF dec ompres sor
are needed to see this pic ture.
Brain Development
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Brain becomes more
hemispherically
specialized
Different brain areas
for different functions
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Frontal
Parietal
Occipital
Temporal
Cerebellum
Brain Areas
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Brain Stem:
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Role in basic
attention, arousal,
and consciousness.
All information to
and from our body
passes through the
brain stem on the
way to or from the
brain.
Brain Areas
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Cerebellum:
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Involved in the
coordination of
voluntary motor
movement, balance
and equilibrium and
muscle tone.
Possibly involved in
working memory.
Brain Areas
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Occipital Lobe:
 The center of
our visual
perception
Brain Areas
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Temporal Lobe:
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Involved in the primary
organization of sensory
input.
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Language is also a
function, especially in
terms of verbal labels
for sensory information.
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The temporal lobes are
highly associated with
memory skills.
Brain Areas
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Parietal Lobe:
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Can be divided into two
functional regions.
The first function
integrates sensory
information to form a
single perception
(cognition).
The second function
constructs a spatial
coordinate system to
represent the world
around us.
Brain Areas
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Frontal Lobe:
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Involved in higher-order
cognitive abilities
Reasoning and decision
making
Also responsible for
planning
Pre-frontal area
involved in working
memory and decision
making
Brain Development
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In terms of differentiation of the different
areas of the brain, this occurs in the
fetus.
Also, early in the fetus, the brain is fairly
smooth, but by the time the infant is
born much of the convolutions and
invaginations have occurred
Brain Development
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After birth, myelination begins and
continues for many years
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Myelination allows speedy transmission of
signals across neurons and between
neurons
Further development of the different
brain areas continue in an inside-out
fashion (subcortical --> cortical)
Brain Development
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The subcortical to cortical development of the
control of behavior has been best
demonstrated via visual behavior
Johnson (1990) suggest that newborns visual
behavior, particularly their eye movements,
are controlled by subcortical pathways
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During the first 6 months, the cortical pathways
functionally develop so that they can influence eye
movements
Johnson (1990)
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One particular hypothesis concerned anticipatory eye
movements
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Required the functioning of mechanisms within the frontal
cortex
Therefore, should not see anticipatory eye movements
before approximately 20 weeks of age
Recent results by Haith, Hazan & Goodman (1988),
Canfield & Smith (1996), and Adler & Haith (in press)
indicate that infants as young as 12 weeks exhibit
anticipatory eye movements
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Indicates that frontal cortex is functional earlier than believed