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Week 15 Online Lesson Summary

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PSYC 100

Week 15: Development 1. Before the Sphinx • Germinal period— the first two weeks after the sperm and egg unite • Gamete— a mature male or female cell used for reproduction • Haploid—a cell that contains only one set of chromosomes • Gametes are haploids • Zygote— a single new cell formed at conception— merging of male and female gametes • Have a full genetic load from receiving half a genome from each game making it a diploid • Diploid— a cell containing both sets of chromosomes • During the germinal period the zygotic cell divides multiple times creating numerous identical copies that are held together in a spherical shape • Cleavage— division of cells in the early embryo to form blastomeres— roughly 24 hours after conception • Morula— solid mass of blastomeres resulting from a number of cleavages of a zygote • Every cell in body have the same DNA in them except gametes • Epigenetic modification is the reason for different cells in our bodies—some genes are turned on and some are turned off • Stem cells— an undifferentiated cell that can divide and produce anyone of a variety of differentiated cells • Have the same DNA but have not undergone epigenetic modification • Any cell in the Morula is interchangeable with any other cell in the Morula because any stem cell can become any specific type of cell • Any one of the cells can develop into a healthy infant because they are so flexible in their development within the uterine environment • Identical twins are formed when the Morula splits into two parts and each part then develops into a fully formed infant • Twins are identical because they came from the same sperm and ovum— same DNA • Fraternal twins develop from the fertilization of two different ovum by two different sperm— different DNA • Up to this point the developing organism has existed in the fallopian tube and is travelling down into the uterus • When the Morula enters the uterus it begins to fill with fluid • Cells being to differentiate— forming two layers o Inner cell mass— the mass of cells inside the Morula that eventually form the embryo o Trophoblast— the cells that for the outer layer of a blastocyst  Protects and transmits nutrients to the inner cell mass • Embryo— the cell development stage preceding the foetus • This differentiation signals the graduation of the developing organism from Morula to blastocyst • Blastocyst— the stage a fertilized egg reaches five to six days after fertilization • The embryonic period begins after implantation in the uterine wall and lasts about 8 weeks • After implantation the tropblast transforms into two parts o The developing embryo is inside the amniotic sac—filled with fluid and maintains a constant environment for the developing organism o The placenta— attaches to the inside of the amniotic sac and the umbilical cord of the embryo  Acts as a filter and protective barrier  Prevents blood of the mother and developing organism from mixing  Transfers nutrients and oxygen from mothers blood  Transforms the organisms waste for elimination by the mother  Block the transfer of many harmful chemicals and infections from the mother to the organism • In this stage the embryo separates into 3 unique layers : 1. Endoderm— the innermost layer of the three primary germ cell layers of the embryo  Develops into the digestive system, urinary tract and lungs 2. Mesoderm— the middle layer of the embryo, lying in between the ectoderm and endoderm  Develops into muscle, bone and circulatory system 3. Ectoderm— the outermost of the three primary layers of the embryo  Develops into skin, hair, teeth, and central nervous system • The developing embryo develops a small tube of ectoderm inside— occurs shortly after 3 layers are differentiated • Neural tube— the embryos precursor to the central nervous system • The neural tube develops into the brain and spinal cord in a process called Neurulation • Neurulation— the formation of the embryonic nervous system, which will then develop into the brain and central nervous system • All of the cells that will make up the CNS will grow inside the neural tube • Neurogenesis— the growth of new neurons— begins 6-7 weeks after conception • Neural migration— the process through which neurons move, grow and connect as the basic neural tube develops into a more mature brain • Genetic instructions help form an outline for how the neurons with grow to interconnect as they develop • Also include the influences of timing and location of neurogenesis, interaction with glial cells and a combination of genetic, chemical and environmental signals • Process is complex and mysterious • During embryonic period a heart will grow and begin to pump blood, most organs will develop, arms and legs will grow and begin to sense and respond in a limited way to sensory stimulation • Toward the end of the period the gonads begin to develop and sexual differentiation begins • Embryonic development proceeds in two patterns: 1. Cephalocaudal— the pattern of embryonic development in which the development occurs most intensely at the head and proceeds downward toward the body 2. Proximodistal— the pattern of embryonic development proceeding from the center of the organism outward • Apoptosis— the genetically programmed process of cell death as part of normal development if the normal functioning of cells and organs— ex: hands growing from flippers • Continues through development • trimming what is not needed is as important as developing connection among the parts that are left • Process is vital through development • The final period of prenatal development is the foetal period— from week 9 to birth • At the start of the stage the foetus is approx. 4cms long • A month later the majority of organ growth is complete • 10 weeks— breathing like motions emerge • Not necessary to obtain oxygen in utero, the chest movements provide muscle and nerve development needed for new born to breathe immediately after birth • End of 4 months— sleep and wake patterns emerge • Movement is large enough to detect— early in development the foetus moves a lot and are crucial to the development of typical nerve and limb growth • Month 5— the vestibular system— balance— develops • Foetus begins to be responsive to sound • heartbeat changes in response to mothers voice— already learned to recognize her voice and will respond more to it then a strangers • Month 6— measures 30cms • foetus would be able to survive premature birth with the aid of doctors, nurses and new drugs— better chance of survival in utero • two weeks later foetus’s heart beat will change in response to light stimulation through abdomen • 6-8 months— spontaneous movement decreases and necessary for the growth of inhibitory neural pathways throughout body • While in womb the foetus will also experience taste • 7 months— begins to grow at a rate of 250 grams per week— continue till born at approx 9 months after conception • Factors can affect the foetal development such as: o Stress:  associated with premature birth and low birth weight— related to reduced growth, higher rates of respiratory problems and other illnesses, lower cognitive ability  offspring often show signs of anxious and depressive-like behaviors after birth and signs of increased aggression o Nutrition:  Food eaten by mother is the only source of nutrients and energy for the foetus— needs these materials to support its rapid and substantial growth  Being healthy and taking supplementary vitamins aids in foetus’s brain development and prevent birth defects o Malnutrition :  Can cause underweight babies with small heads  Physical malformations  High risk for developing diseases throughout the rest of their lives o Teratogens:  External compounds that cause extreme deviations from typical development if introduced to the developing organism  Include heavy metals like mercury, some medications, tobacco and alcohol  Cause death of foetus if exposed very early— timing of exposure will influence which body parts with be affected  Every foetus will be affected differently  The greater amount and length of exposure will have more drastic effects on the developing organism 2. Four Legs: • The presence of strong reflexes at birth are important for survival and indicate typical neural development • Some are highly useful behaviors that last lifetimes— ex: eye blink • Others are useful at birth but disappear or replaced by voluntary behaviors— ex: rooting and sucking • Some of the reflexes purpose at birth are less straightforward and not understood why they exist o Babinski reflex— fan and then curl toes when foot stroked
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