ch3: prenatal development

germinal period duration

first 2 weeks

embryonic period duration

3-8 weeks

fetal period duration

9 weeks until birth

biology of germinal period

• ovary produces ovum, which is fertilized within fallopian tube by sperm

• the resulting zygote travels down fallopian tube

• cell division produces the blastocyst, which implants into uterine wall

implantation in the germinal period

when the zygote successfully adheres to the uterine wall

monozygotic (identical) twins

occurs when the mass of cells inside the blastocyst divides into two sets

dizygotic (fraternal) twins

occurs with two ovaries mature at the same time + fertilized by two different sperm cells

characteristics of embryonic period

• most vulnerable development period

• about 20-30% of pregnancies in this period result in miscarriages

• formation of the neural tube

• development of cardiovascular system

prenatal brain development

• neurogenesis (making neural cells)

• neuronal migration

• neural differentiation

• formation of neural connections

brain growth during embryonic period

• primitive areas of the brain start developing at 25 days

• forebrain expands into cortex, which surrounds inner areas of brain + leaves cerebellum and brainstem exposed at the bottom

• all major structures of the brain are present at birth but will not reach mature function for two more decades

neurons

• the basic information-processing cells of the brain

• begin to be produced in 3rd-5th week of embryonic period through neurogenesis

prenatal brain development

• neuronal migration starts around 6th week when neurons move from center of neural tube out to form brain

• neural differentiation happens at same time as neuronal migration

• synapses form

• neurons that fail to make connections degenerate quickly

pain perception paradox

• pain needs thalamocortical connections: developed in 24-28 weeks

• preterm babies show behavioral, hormonal, physiological responses to pain even earlier

• the cortical subplate forms the fetus’ first cortical network

six main sets of environmental influences on prenatal development

• cigarettes

• alcohol

• drugs of abuse

• maternal diseases

• maternal diet

• health of the father