Prenatal Development

Prenatal Development • 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) • 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) • All major internal and external structures form • Three layers of cells • Endodermal - internal organs • Ectodermal - nervous system, eyes, ears, skin • Mesodermal - muscles, bones, heart • Major brain development in week 5

Neurulation (week 3-4)

Stage 2 (Cont.) • Head is 50% of mass

Developmental Course

Stage 3: Fetus (9 - 38 weeks) • Further development of body so at birth head is only 25% of mass

Stage 3 (Cont.) • 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.) • 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.) • Later development includes progress in the brain, lungs, development of fat that allows at least some breathing, temp regulation • greater viability if premature • In month 8, immune system starts to pick up with help from mom

Neural Development • By the end of infancy the volume of neurons has increased significantly

Neural Development • The density, however, has decreased

Neural Development • 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

Neural Development • Stages: • Cell Production - Fetus • Cell Migration - 7 mos. • Cell Elaboration • Culling • Myelination - 4 yrs.

Brain Development • Brain becomes more hemispherically specialized • Different brain areas for different functions • Frontal • Parietal • Occipital • Temporal • Cerebellum

Brain Areas • Brain Stem: • 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 • Cerebellum: • Involved in the coordination of voluntary motor movement, balance and equilibrium and muscle tone. • Possibly involved in working memory.

Brain Areas • Occipital Lobe: • The center of our visual perception

Brain Areas • Temporal Lobe: • Involved in the primary organization of sensory input. • Language is also a function, especially in terms of verbal labels for sensory information. • The temporal lobes are highly associated with memory skills.

Brain Areas • Parietal Lobe: • 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 • Frontal Lobe: • 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 • 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 • After birth, myelination begins and continues for many years • 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 • 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 • During the first 6 months, the cortical pathways functionally develop so that they can influence eye movements

Johnson (1990) • One particular hypothesis concerned anticipatory eye movements • 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 • Indicates that frontal cortex is functional earlier than believed

Prenatal Development