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)

EctodermNeuralGroove

Notochord

NeuralPlate

Ectoderm

NeuralGroove

Notochord

NeuralPlate

SurfaceEctoderm

NeuralTube

Notochord

NeuralCrest

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

Volume (mm3)

0 1500 3000 4500

28 wk GANewborn

6 days2 wk2 mo4 mo

19 mo3.75 yr

5 yr11 yr13 yr26 yr

Neural Development

The density, however, has decreased

Neurons/mm3(x104)

0 10 20 30 40 50 60 70

28 wk GANewborn

6 days2 wk2 mo4 mo

19 mo3.75 yr

5 yr11 yr13 yr26 yr

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 0

1234567

28 wkGA

2 mo 8 mo 2 yr 10 yr 70 yr

synapse/mm3 total synapse

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 0

2000400060008000

1000012000140001600018000

28 wkGA

2 mo 8 mo 2 yr 10 yr 70 yr

synapse/neuron

Neural Development Stages: Cell Production -

Fetus Cell Migration - 7

mos. Cell Elaboration

Culling Myelination - 4 yrs.

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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