Prenatal DevelopmentPrenatal Development

Nerve growth Nerve growth begins when a begins when a sheet of cells on sheet of cells on the back of the the back of the embryo folds in the embryo folds in the middle to form the middle to form the future spinal cord. future spinal cord. At one end, the At one end, the tube enlarges to tube enlarges to form the brain’s form the brain’s major sections.major sections.

Prenatal DevelopmentPrenatal Development

Fetal DevelopmentFetal Development

First responses are reflexes.First responses are reflexes.

Touch develops early, as early as 7-1/2 weeks.Touch develops early, as early as 7-1/2 weeks.

By 15 weeks, fetus can grasp, frown, squint, By 15 weeks, fetus can grasp, frown, squint, grimace.grimace.

At 20 weeks nerve-cell production slows, At 20 weeks nerve-cell production slows, existing cells grow larger and make more existing cells grow larger and make more complex connections. Taste and smell formed.complex connections. Taste and smell formed.

Around 24 weeks fetus can feel movement Around 24 weeks fetus can feel movement and may respond to sound.and may respond to sound.

Final Stages of Fetal Final Stages of Fetal DevelopmentDevelopment

Age of viability Age of viability – About 25 – About 25 weeks, if born about 50% weeks, if born about 50% chance of survival.chance of survival.

25 weeks – nerve supply to 25 weeks – nerve supply to ear completeear complete

26 weeks – response to touch26 weeks – response to touch 27 weeks – response to light27 weeks – response to light 29 weeks – eyes open in womb29 weeks – eyes open in womb 32 weeks – start of 32 weeks – start of

‘awareness’ neural circuits ‘awareness’ neural circuits advanced as a newborn’sadvanced as a newborn’s

35 weeks – fetus begins to 35 weeks – fetus begins to develop daily activity cyclesdevelop daily activity cycles

Birth rate: # of live births per 1000 peopleBirth rate: # of live births per 1000 peopleInfant Mortality: # of infant deaths under 1 year of Infant Mortality: # of infant deaths under 1 year of age per 1000 live birthsage per 1000 live births

Birth RateBirth RateInfant MortalityInfant Mortality

U.S.U.S. 14 14 6.37 6.37 Afghanistan Afghanistan 47 47 163.0 163.0 AustraliaAustralia 12 12 4.57 4.57 CanadaCanada 10 10 4.63 4.63 ChinaChina 13 13 24.2 24.2 IraqIraq 32.5 32.5 50.3 50.3

JapanJapan 9.5 9.5 2.8 2.8

Some Principles of Some Principles of DevelopmentDevelopment

Rules of MaturationRules of Maturation Follows an orderly sequenceFollows an orderly sequence Rate is Rate is notnot uniform uniform Follows physiological gradientsFollows physiological gradients

CephalocaudalCephalocaudal 250,000 neurons per min.250,000 neurons per min. 60% adult size at birth60% adult size at birth

ProximodistalProximodistal Principle of motor primacy – neuromuscular Principle of motor primacy – neuromuscular

structures of the body structures of the body mustmust reach certain reach certain levels of maturation before they can respond levels of maturation before they can respond to stimulationto stimulation