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Lecture 2

PSYC 251 Lecture Notes - Lecture 2: Spina Bifida, Neural Tube Defect, Programmed Cell Death

Course Code
PSYC 251
Stanka A Fitneva

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PSYC 251 January 16, 2018
Lecture 2
Early Developmental Processes
Conception and Stages
- Prenatal Development
o Early researchers thought miniature man or homunculus lived in sperm and this
grew into a baby in the womb
This concept was known as preformationism: tiny human just grows
Eliminates the woman from the picture, making the father the sole parent
o Aristotle rejected this and embraced epigenesism: development from an egg
through a series of processes such that the result is very different from the initial
o People claimed to see homunculus through early microscopes, showing that
people will see what they want to see
- Germ cells
o Produced through meiosis
o Have 23 chromosomes
o Women born with all eggs, while men make sperm continuously
Egg (largest cell in the body) moves through fallopian tube and releases
chemical substance to serve as beacon and, to help to prepare uterus
o Average of 500 million sperm released every time a man ejaculates
A sperm is purely genetic material and a tail
Takes 6 hours to travel 6-7 inches
Only 200 get close
Some fail due to change, traffic jam, or wrong direction, or are genetically
- Developmental Process
o Cell division
Begins within the first 12 hours of the egg and sperm coming together
o Cell migrations
Occurs during embryonic period (after egg implantation)
o Cell differentiation
All cells are stem cells in germinal period and then cell differentiation
350 types of cells
Location of cells determines type
o Programmed cell death (apoptosis)
Important to proper development ie. webbing and tail must die off
o Hormonal effects
All fetuses are born so that they can become male or female
Presence of testosterone is what allows for males to develop
- Germinal Period
o A blastocyst is a hollow sphere with inner cell mass
o <1 mm in diameter
o Identical twins occur due to a splitting of inner cell bass
o Complete implantation marks the end of the germinal period
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PSYC 251 January 16, 2018
Lecture 2
Takes a week for the blastocyst to reach the uterus
Implantation takes about a week
Two weeks total
o Differentiation starts after implantation
- Period of the Embryo
o Begins roughly 2 weeks after conception (after full implantation)
o In second week of this period, the organism develops three layer
Ectoderm = outermost layer
Nervous system, teeth, nails, inner ear, eye lens, epidermis
Mesoderm = middle layer
Muscles, bones, circulatory system, skin
Endoderm = innermost layer
Digestive system, lungs, urinary tract, glands
o U-shaped groove forms down centre of ectoderm, creating the neural tube
One end will swell to become the brain and spinal cord
If this groove doesn’t close properly, you get spina bifida
o Placenta is formed in this early period
Ensure that baby’s blood doesn’t mix with the mother’s
Provides nutrients
Many things can move across placental barrier, including alcohol
o Amniotic sac is formed
Provides a constant temperature and allows for exercise, since the fluid
reduces the effects of gravity on the baby
Filled with fluids to protect the baby from being jarred if mother is
(protects baby)
- The Period of the Embryo
o Very fast; most rapid stage
o Between weeks 3 and 8 post conception
o Goes from ball of cells into miniature human
o Development proceeds in cephalocaudal (head to tail) and proximodistal (inside
to outside) manner
o At week 4, the heart is beating but, otherwise, there is very little function or
differentiation among cells
o Rapid development of brain and face between weeks 6 and 6
This stage is very sensitive to teratogens
Fetus starts to move but is too small for mom to feel
- Fetus at 11-12 Weeks
o Fingers and external genitalia are fully formed
o Reflexes present and moving a lot but still not felt
o Organs, muscles, and nervous system are becoming organized and connected
- Fetus at 16 Weeks
o Mom begins to feel babies’ first kicks
o Beginning of period of lower body growth
o Head is less disproportional to rest of body
- Fetus at 18 Weeks
o Starts sucking thumb
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PSYC 251 January 16, 2018
Lecture 2
o Becomes covered in vernix (that gross stuff on a baby)
Protects baby from sitting in liquid so it doesn’t look like a prune
- Fetus at 20 Weeks
o More head-down position
o Less movement
o Putting on weight (baby fat)
o Facial expressions begin
o Shields eyes from fetoscope (light shone into uterus through vagina during
examination) when it is examined
o May survive at 20-22 weeks with lots of intervention if born premature
Lungs aren’t fully developed
Minimal body fat so must have temperature regulated
Brain isn’t developed so baby is very over reactive because it’s not
supposed to be exposed to all the stimulus of the external environment
- Fetus at 28 Weeks
o Age of viability: can survive without major medical intervention if born
Brain and lungs are developed enough
Still at risk of major developmental disorders but odds of survival are
much better
o Eyes open and move
o Auditory system is working
o In last 3 months, fetus triples in weight and fat develops under the skin
Prenatal Behaviour and Learning
- Fetal Behaviour - Movement
o Fetal movement starts at 5-6 weeks post conception
Earliest movement is hiccups; could be a practice for being burped once
Can move its limbs, hands/feet, head, eyes, mouth
o Swallowing (takes in amniotic fluid and it passes through digestive system and
then is excreted; helps digestive system develop and prepares them to swallow
milk; helps their palate develop)
o Fetal breathing (brings amniotic fluid into and out of their lungs)
Starts at 10 weeks
o Most movement is present by 12 weeks but the fetus is too small for it to be felt
o Movement is almost constant from 5-10 weeks but, by 10 weeks, you see periods
of rest, resulting in cycles
o By third trimester, fetus moves only 20-30% of the time, mostly because the
space is more cramped, and they start to sleep
o Circadian rhythms appear
Less activity in early morning and more activity in evening
Individual differences in activity continue in postnatal period
- The Fetal Experience
o Touch
Experiences tactile stimulation
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