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

Prenatal Development

Fetal 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, grimace. By 15 weeks, fetus can grasp, frown, squint, grimace. At 20 weeks nerve-cell production slows, existing cells grow larger and make more complex connections. Taste and smell formed. At 20 weeks nerve-cell production slows, existing cells grow larger and make more complex connections. Taste and smell formed. Around 24 weeks fetus can feel movement and may respond to sound. Around 24 weeks fetus can feel movement and may respond to sound.

Final Stages of Fetal Development Age of viability – About 25 weeks, if born about 50% chance of survival. Age of viability – About 25 weeks, if born about 50% chance of survival. 25 weeks – nerve supply to ear complete 25 weeks – nerve supply to ear complete 26 weeks – response to touch 26 weeks – response to touch 27 weeks – response to light 27 weeks – response to light 29 weeks – eyes open in womb 29 weeks – eyes open in womb 32 weeks – start of ‘awareness’ neural circuits advanced as a newborn’s 32 weeks – start of ‘awareness’ neural circuits advanced as a newborn’s 35 weeks – fetus begins to develop daily activity cycles 35 weeks – fetus begins to develop daily activity cycles

Birth rate: # of live births per 1000 people Infant Mortality: # of infant deaths under 1 year of age per 1000 live births Birth RateInfant Mortality Birth RateInfant Mortality U.S U.S Afghanistan Afghanistan Australia Australia Canada Canada China China Iraq Iraq Japan Japan

Some Principles of Development Rules of Maturation Rules of Maturation Follows an orderly sequence Follows an orderly sequence Rate is not uniform Rate is not uniform Follows physiological gradients Follows physiological gradients Cephalocaudal Cephalocaudal 250,000 neurons per min. 250,000 neurons per min. 60% adult size at birth 60% adult size at birth Proximodistal Proximodistal Principle of motor primacy – neuromuscular structures of the body must reach certain levels of maturation before they can respond to stimulation Principle of motor primacy – neuromuscular structures of the body must reach certain levels of maturation before they can respond to stimulation