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Week 15 PSYCH online reading.docx

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PSYC 100

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PSYCH – Week 15 Online Readings Week 15: Development Focus Question: Is there prenatal psychology? Introduction to Development Human development begins before birth and continues until we die. We develop from the merging of two cells into a being made up of hundreds of billions of cells. The prenatal period is a crucial time, not just for physical development but also for sensory and cognitive development. Events during gestation can have profound effects on later life outcomes. Prenatal Development Germinal Period – the first two weeks after the sperm and egg unite. Will last until the developing cells have attached to the uterine wall, about 8-10 after conception. Sperm and ova are both a specialized type of reproductive cells called a gamete. Gametes are haploid, meaning that each contains only half of the genetic component required for life; gametes are the only haploid cells in the body. The result of the merging of male and female gametes is the zygote. Gamete + gamete = diploid, which has a full genetic load. During the germinal period, the zygotic cell divides multiple times, creating numerous identical copies that are all held together in a spherical shape. These divisions occur through a process called cleavage, which begins roughly 24 hours after conception. The resulting spherical mass of cells is known as a morula: a solid mass of blastomeres resulting from a number of cleavages of a zygote. Epigenetic Modification – Some genes are turned on and others are turned off, which leads to differential expression of proteins and eventually different cellular properties and functions. Stem Cells –An undifferentiated cell that can divide and produce any one of a variety of differentiated cells as it has not yet undergone epigenetic modification.Any cell in the morula is essentially interchangeable with any other cell. - Identical twins are formed when the morula splits into two parts and each part then develops into a fully formed infant. They are identical because each came from the same sperm and ovum, hence the same DNA. - Fraternal twins develop from the fertilization of two different ova by two different sperm, thus have different DNAand are not more alike genetically than other sets of siblings. Blastocyst stage – The stage a fertilized eggs reaches five to six days after fertilization. The developing organism has gone down the fallopian tube and into the uterus which fills with fluid. At this point cells begin to differentiate, forming two layers called the inner cell mass and the trophoblast. The inner cell mass is a group of cells that will eventually grow into the embryo, whereas the trophoblast layer forms a surrounding later that both protects the inner cell mass and transmits nutrients to it. This differentiation signals the graduation of the developing organism from morula to blastocyst. The trophoblast eventually develops into the extra-embryonic tissures, including the placenta, and controls the exchange of oxygen and metabolites between the mother and embryo. Embryonic period – begins after implantation in the utherine wall and lasts about 8 weeks. After implantation, the embryo consists of hundreds of cells. The trophoblast layer transforms into two parts. The developing embryo resides within the first part, the amniotic sac, which is filled with fluid and maintains a constant environment for the developing organism. The second part, the placenta, attaches to the inside of the amniotic sac and the umbilical cord of the embryo. The placenta acts as a filter and protective barrier for the developing organism. It prevents the blood of the mother and the developing organism from mixing, transfers nutrients and oxygen from the mother’s blood to the developing organism, and transforms the organism’s waste for elimination by the mother. The placenta also blocks the transfer of many harmful chemicals and infections from the mother to the organism. In this stage, the embryo separates into three unique layers: the endoderm, mesoderm, and ectoderm. The endoderm, the innermost layer of tissue, eventually develops into the digestive system, urinary tract, and lungs. The mesoderm, the middle layer, transforms into muscle, bone, and the circulatory system. The ectoderm, the outer layer, develops into skin, hair, teeth, and the central nervous system. Embryotic Period Process of neurulation – a small tube of ectoderm forms inside the embryo, becoming the neural tube, and begins to develop into the brain and spinal cord. All of the cells that will make up the central nervous system will grow inside this neaural tube. The growth of new neurons is called neurogenesis, and begins 6-7 weeks after conception. Migration and Growth Although neural growth occurs at a breathtaking pace, most people’s brains at birth are remarkably similar. For this process to occur sensibly, the cells must move about and organize themselves spontaneously and appropriately. This movement, neural migration, works through a combination of factors. Genetic instructions apparently help form an outline for how the neurons will grow to interconnect as they develop into a more mature brain. Other factors influencing migration include the timing and location of neurogenesis; interaction with glial cells; and a combination of genetic, chemical, and environmental signals. The exact mechanisms of this process are extremely complex and remain largely mysterious. During the embryonic period, the embryo will also grow a heart and begin to pump blood, begin to develop most of its organs, begin to grow arms and legs, and begin to sense and respond in a limited way to sensory stimulation. Toward the end of this period, the gonads begin to develop and sexual differentiation begins. Embryonic development proceeds according to two patterns. The first pattern is cephalocaudal, which means that development occurs most intensely at the head and proceeds downward toward the body. Development also occurs in a proximodistal pattern, proceeding from the center of the organism outward. Apoptosis Apoptosis: process of cell death that is genetically programmed and is required for typical development. An example of apoptosis in prenatal development is shown by the hand, which develops at first as an almost fin-like appendage.Apoptosis occurs when the cells that exist between what will be the fingers die, removing the initially present webbing. Foetal Period – The final period of prenatal development continues from the ninth week after conception until birth. At the start of this stage, the foetus weighs only 30 grams and is approximately 4 cm long.Amonth later, the majority of organ growth is complete.As early as 10 weeks of age, the foetus begins making breathing-like motions. Though not necessary to obtain oxygen in utero, these chest movements provide the muscle and nerve development needed for the newborn to breathe immediately after birth.At the end of the fourth month, sleep and wake patterns begin to emerge. Though the growing organism has been moving for several weeks at this point, the foetus is now large enough for the mother to detect its movements. Early in development, the foetus moves a great deal, and these spontaneous movements have been shown to be crucial to the development of typical nerve and limb growth. During the fifth month, the vestibular system, which is required for a sense of balance, begins to develop.Around this time, the foetus also becomes responsive to sound.At this stage, the foetal heartbeat changes in response to the sound of its mother’s voice, and the foetus already has learned to recognize her voice and will respond to it more than to strangers’voices About six months after conception, the foetus weighs around 700 grams and measures nearly 30 cm long.At this stage of development, with the intervention of doctors, nurses, and new drugs, the foetus can survive premature birth. However, its odds of survival increase substantially the longer it remains in utero. Two weeks later, the foetus’s heartbeat will change in response to light stimulation through the mother’s abdomen. From six to eight months after conception, the spontaneous movement of the foetus decreases, which is thought to be necessary for the growth of inhibitory neural pathways throughout the body. While in the womb, the growing foetus will also experience taste. In one experiment, it was shown that when infants begin to eat solid food, they show a preference for foods that their mother ate while pregnant and breastfeeding. Beginning at about seven months after conception, the foetus will begin to grow at a rate of approximately 250 grams per week. It will continue to grow at this rate until it is born, approximately nine months after conception. Stress and Nutrition Good nutrition during pregnancy, as well as supplementing the mother’s diet with vitamins and minerals such as folic acid, vitamin B-12, calcium, and iron, has been shown to aid brain development and prevent some birth defects. Conversely, both maternal stress and poor nutrition can lead to low birth weight, higher rates of illness, and other developmental difficulties. Stress One factor that has been shown to have an effect on prenatal development is maternal emotional state. High levels of stress during pregnancy have been associated with both premature delivery and low birth weight (both of which are associated with many negative outcomes, such as reduced growth, higher rates of respiratory problems and other illnesses, and lower cognitive ability). Other studies have shown that when mothers experience high levels of stress during pregnancy, their offspring will often show signs of anxious and depressive-like behaviour after birth, as well as signs of increased aggression. Nutrition Another important factor affecting the developing organism is the mother’s nutrition during pregnancy. The food she eats is the only source for the growing organism to obtain its own nutrients and energy and the materials it needs to support its rapid and substantial growth. Eating healthy food, as well as supplementing one’s diet with vitamins and minerals such as folic acid, vitamin B-12, calcium, and iron, has been shown to aid brain development and prevent some birth defects. Malnutrition Poor nutrition, which often occurs in people who have been affected by poverty or famine, can have an adverse effect on development. One example of these negative effects is found in a study examining birth outcomes of women in the Netherlands during World War II. In response to the Dutch government’s support of the invadingAllied forces, the German military enforced a food embargo on the Netherlands from 1944 to 1945. Researchers studied the effects of the resulting famine on infants born shortly afterwards and discovered that they showed serious developmental effects. Women who were late in their pregnancies at the beginning of the famine had underweight babies with small heads, whereas women who were not as far along in their pregnancies had babies with serious physical malformations. Further studies of people born during this famine noted that they remained at higher risk for developing diseases throughout the rest of their lives. Teratogens Teratogens are external compounds that can cause extreme deviations from typical development if introduced to the developing organism. There are many different types of teratogens, including heavy metals like mercury, some prescription medications, and alcohol. Their effects vary, but certain rules appear to apply across most cases. Childhood and Reflexes The newborn baby comes into the world with a number of behaviours already in place. Many are reflexes, specific complex actions that occur automatically in response to certain stimuli. When infants feel something on one of their cheeks, they turn their head toward the touch and open their mouth (the rooting reflex). This reflex is crucial to feeding but is soon replaced by voluntary behaviours. The presence of strong reflexes at birth is not only important for infant survival; it’s also a good indicator of typical neural development. Some reflexes are highly useful behaviours tha
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