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03 - Lifespan Development.docx

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Queen's University
PSYC 100

Week Three: Lifespan Development Is there prenatal psychology? Before the Sphinx Germinal Period The 8-10 days after the sperm and egg unite, before the developing cells attach to the uterine wall  Sperm and ova are specialized type of reproductive cell called a gamete, and both are haploid (contain only one set of chromosomes / half the genetic complement required for life)  The result of the merging male and female gametes is the zygote, which contains a full genetic load (half from each gamete), making is a diploid  The zygotic cell divides multiple times during the germinal period, through a process called cleavage (forming blastomeres) which begins 24 hours after conception, and creates a spherical mass of cells called a morula (solid mass of blastomeres)  Identical twins are formed when the morula spits into two parts and each part fully develops into a fully formed infant – they are identical because they share the same DNA Epigenetics:  Every cell in your body (except for gametes) has identical DNA, however they all act differently…  Epigenetic modification means that some genes are turned on and others are turned off, leading to differential expression of proteins and eventually different cellular properties and functions  Stem cell: an undifferentiated cell that has not yet undergone any epigenetic modification – can divide and produce any one of a variety of differentiated cells Embryonic Period Begins after implantation in the uterine wall and lasts about 8 weeks  When the morula makes it down the fallopian tube into the uterus, it begins to fill with liquid  Here the cells begin to differentiate, forming two layers: o Inner Cell Mass: mass of cells inside morula that will eventually form the embryo o Trophoblast: outer layer protecting the inner cell mass and transmitting nutrients to it – eventually develops into the extra embryonic tissues, including the placenta  This differentiation signals means the organism has gone from morula to blastocyst  Trophoblast layer soon transforms into two parts: o The Amniotic Sac, which is filled with liquid and provides a constant environment o The Placenta, which attaches the sac with the umbilical cord; this provides a filter and protective barrier for the embryo, preventing the blood of the mother and organism from mixing, while transferring nutrients and waste between the two  The embryo separates into three layers: o Endoderm: innermost layer – later develops into digestive system, urinary tract, lungs o Mesoderm: middle layer – develops into muscle, bone, and the circulatory system o Ectoderm: out layer – develops into skin, hair teeth, and central nervous system  Ectoderm folds in on itself creating a small tube inside the embryo called the neural tube, which begins to develop into the brain and spinal cord through neurulation  Neurogenesis: growth of new neurons – cells grow inside neural tube beginning at 6-7 weeks  Neural Migration: process through which neurons move, grow, and connect as the basic neural tube develops into a more mature brain; all early brains are similar – how? Genetic instructions, timing and location of neurogenesis, interaction with glial cells, etc. – still mysterious  Embryonic development proceeds with two simultaneous patterns: o Cephalocaudal: development occurs intensely at the head and proceeds downwards o Proximodistal: proceeding from the center of the organism outward  Apoptosis: genetically programmed process of cell death as part of normal development or the normal functioning of cells and organs (e.g. hand goes from fin-like to fingers as web cells die) Foetal Period This final period continues from the ninth week after conception until birth  At the beginning of this stage the foetus weighs 30 grams and is 4cm long  At 10 weeks breathing-like motions are seen, with full organ development seen a month later  At 4 months, sleep and wake patterns emerge, and movement can be felt by the mother  During the 5 month, the vestibular system (required for sense of balance) begins to develop; the foetus also becomes responsive to sound, and recognize the mothers voice  At 6 months, the foetus weighs around 700 grams and is 30 cm long – can survive birth  Two weeks later, the foetus will respond to light and can taste  From 6-8 months, movement decreases to allow growth of inhibitory neural pathways  While this path is typical, many factors can affect growth (e.g. nutrition, stress) o Stress – premature delivery and low birth weight, anxiety/depression and aggression o Good Nutrition – typical brain development and prevention of some birth defects o Malnutrition – underweight babies with small heads and serious physical malformations  Teratogens: external compounds that can cause extreme deviations from typical development if introduced to the developing organism (e.g. mercury, medications, alcohol) o Timing: more likely to cause death if exposed earlier on, influences body parts affected o Individuality: depending on the mother and foetus, teratogens affect each differently o Amount: greater amount and exposure time, the more drastic the effects Four Legs How do our behaviours and mental processes change during early childhood? Typical Childhood Development Reflexes  Presence of strong reflexes at birth is a good indicator of
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