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If Pavlov is correct about the notion of the reflex, what is the relationship between human experience and environmental input?  Where does this formulation leave the “mind”?  What did Watson suggest for the concept of the mind in psychology?

• Face is forming with rudimentary eyes, ears, mouth, and tooth buds

• Arms and legs are moving • Brain is forming

• Fetal heartbeat is detectable with ultrasound

• Is called an “embryo”

12 weeks • Is about 3 inches long and weighs about 1 ounce

• Can move arms, legs, fingers, and toes

• Fingerprints are present • Can smile, frown, suck, and swallow

• Sex is distinguishable

• Can urinate

• Is called a “fetus”

Second trimester (middle 3 months)

16 weeks • Is about 6 inches long and weighs about 4 to 7 ounces

• Heartbeat is strong

• Skin is thin, transparent

• Downy hair (lanugo) covers body

• Fingernails and toenails are forming

• Has coordinated movements; is able to roll over in amniotic fluid

20 weeks • Is about 12 inches long and weighs close to 1 pound

• Heartbeat is audible with ordinary stethoscope

• Sucks thumb

• Hiccups

• Hair, eyelashes, eyebrows are present

24 weeks • Is about 14 inches long and weighs about 1 to 1½ pounds

• Skin is wrinkled and covered with protective coating (vernix caseosa)

• Eyes are open

• Waste matter is collected in bowel

• Has strong grip

Third trimester (last 3 months)

28 weeks • Is about 16 inches long and weighs about 3 pounds

• Is adding body fat

• Is very active

• Rudimentary breathing movements are present

32 weeks • Is 16½ to 18 inches long and weighs 4 to 5 pounds

• Has periods of sleep and wakefulness

• Responds to sounds

• May assume the birth position

• Bones of head are soft and flexible

• Iron is being stored in liver

36 to 38 weeks • Is 19 to 20 inches long and weighs 6 to 7½ pounds

• Skin is less wrinkled

• Vernix caseosa is thick

• Lanugo is mostly gone

• Is less active

• Is gaining immunities from mother

Figure 8 Growth and Development in the Three Trimesters of Prenatal Development(Top) ©

David Spears/PhotoTake, Inc.; (middle) © Neil Bromhall/Science Source; (bottom) © Brand X Pictures/PunchStock RF

The Brain One of the most remarkable aspects of the prenatal period is the development of the brain (Bale, 2015; Stiles & others, 2015). By the time babies are born, they have approximately 100 billion neurons, or nerve cells, which handle information processing at the cellular level in the brain. Page 52 During prenatal development, neurons move to

specific locations and start to become connected. The basic architecture of the human brain is assembled during the first two trimesters of prenatal development. In typical development, the third trimester of prenatal development and the first two years of postnatal life are characterized by connectivity and functioning of neurons (Nelson, 2012). Four important phases of the brain’s development during the prenatal period involve (1) formation of the neural tube; (2) neurogenesis; (3) neural migration, and (4) neural connectivity.

As the human embryo develops inside its mother’s womb, the nervous system begins forming as a long, hollow tube located on the embryo’s back. This pear-shaped neural tube, which forms at about 18 to 24 days after conception, develops out of the ectoderm. The tube closes at the top and bottom ends at about 24 days after conception. Figure 9 shows that the nervous system still has a tubular appearance 6 weeks after conception.

Figure 9 Early Formation of the Nervous System

The photograph shows the primitive, tubular appearance of the nervous system at six weeks in the

human embryo.© Claude Edelmann/Science Source

Two birth defects related to a failure of the neural tube to close are anencephaly and spina bifida. When a fetus has anencephaly (that is, when the head end of the neural tube fails to close), the highest regions of the brain fail to develop and the baby dies in the womb, during childbirth, or shortly after birth (Steric & others, 2015). Spina bifida, Page 53an incomplete development of the spinal cord, results in varying degrees of paralysis of the lower limbs. Individuals with spina bifida usually need assistive devices such as crutches, braces, or wheelchairs. Both maternal diabetes and obesity also place the fetus at risk for developing neural tube defects (McMahon & others, 2013; Yu, Wu, & Yang, 2016). Further, a recent study revealed that a high level of maternal stress during pregnancy was associated with neural tube defects in offspring (Li & others, 2013). A strategy that can help to prevent neural tube defects is for women to take adequate amounts of the B vitamin folic acid (Bergman & others, 2016). A recent large-scale study in Brazil found that when flour was fortified with folic acid it produced a significant reduction in neural tube defects (Santos & others, 2016). In a normal pregnancy, once the neural tube has closed, a massive proliferation of new immature neurons begins to take place about the fifth prenatal week and continues throughout the remainder of the prenatal period. The production of new neurons is called neurogenesis. At the peak of neurogenesis, it is estimated that as many as 200,000 neurons are being generated every minute.

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