Aantekeningen hoorcollege 2 - Development, Learning & Behavior - Universiteit Utrecht (2022/2023)

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Prenatal development

WEIRD science

• Western, Educated, Industrialized, Rich, Democratic
• These are characteristics of the societies researchers typically gather their data from
• 95% of the participants in social sciences cover 12% of the world population
• Participants are in generally not very representative for WEIRD people
• What we know about development and what we tend to regard as normal and abnormal may only be valid for a selective part of human kind
  
  • This means we should be careful with generalizing are knowledge and use it as a golden standard for comparisons and assessments
  • It also means we should include more diverse samples in our research

What is development?

A specific type of change

• Qualitative » changes in what there is (not in how much)
• Sequential » over development some changes precede others (they need to proceed before other development can take place)
• Cumulative » one developmental stage can build upon other developmental stages
• Directional » during development things can be build up (progressive) or broken down (regressive)
• Multifactorial » there is not one factor determining the course of development
• Individual » developmental pathways are unique for each individual

Prenatal development

• Around 20 weeks the female egg cells develop in the embryo
• Each cell contains a full complement of genetic material (the ‘instruction manual’/blueprint that tells the cell what to be and what to do). This information is described in our genes, and our genes are organized in 23 pairs of chromosomes, 46 in total)
• Cell division
  
  • Normal: mitosis » all genetic material is neatly copied and then separated into two full sets so that after the cell division is completed, the resulting to cells each contain an identical full copy of your entire genetic code.
  • Special: meiosis » after the genetic material is copied the dead mom-pairs of chromosomes first exchange genetic information between each other (= crossing over). After that they make a first split, and then split again, ending up with 4 new cells, that each contain a different combination of genetic codes. Each of these 4 new cells contain only half of the blueprint. The other half will be delivered by the other … when the egg is fertilized by the sperm cell.
• The process of cell division is the basis for genetic variation
  
  • And therefore the genetic basis for individual differences in all kinds of development
  • It helps us understand the interaction between nature and nurture
    
    • Monozygotic twins come from a single zygote, a fertilized egg cell, and therefore share the exact same genetic material
    • Dizygotic twins develop from different zygotes and thus are not genetically identical

The moment the egg is fertilized by a sperm cell:

• With the complete ‘blueprint’ the egg starts to develop in a full sized baby
• 4 developmental processes:
  
  • Mitosis: normal/’ordinary’ cell division. After the egg cell is fertilized, the zygote starts to divide at a very rapid pace
  • Cell migration: all the cells that are created need to go to designated positions in the body (some cells are pushed away by the cells formed during cell division, other cells actively migrate to new positions)
  • Cell differentiation: the fertilized egg cell (zygote) starts to divide rapidly. Soon there is a lump of the same cells (morula) and they can become anything, there not yet specialized (totipotent). The number of cells increase, but the size of the morula stays the same. Thus, pressure is created. This pressure is the trigger for the first type of differentiation:
    
    • Some cells become blastocyst (that later become the fetal part of the placenta)
    • The other cells become the inner mass cells (pluripotent » the cells can’t become part of the placenta anymore but they can become any type of tissue in the human body). What they will become/how they will differentiate depends on the neuro-chemical signals they receive during the development. Once they are specialized into their final form, they can’t change anymore.
  • Apoptosis: programmed cell death.

Influences on the fetus while developing

• Stimulation from the outside
  • 10w » sense of pressure
  • 13w » detection of movements
  • 20w » detection of light (even before they can open their eyes)
  • 26w » detection of sounds
  • 26-28w » detection of smell and test
• Fetal movement
  
  • 5-6w » bending head and spine
  • 8-9w » startle like movements (like hiccups)
  • 10w » variety of limb movements
  • 10-11w » head and breathing movements
  • 11-12w » yawn, suck, swallow amnionic fluid
  • 14w » nonrandom movements (about 66% of the movements the child makes are directed to objects in its environment)
  • 20w » movements with all parts of their face
  • 25w » opening and closing eyes
• Function of fetal movement
  
  • Swallowing » oropharyngeal cavity (back of throat), lungs, digestive system
  • Body movements » muscles, bones, joints, skin
• Drinking alcohol during pregnancy is damaging because alcohol is a sedative and it reduces the amount of movement the fetus makes. When the fetus moves less, it effects the development

Teratogens

= harmful influences on the developing fetus

• Three forms:
  • The state of the mother
  • Diseases
  • Chemicals
• Timing, duration and the amount of exposure are important determinisms of the severity of the effects on development, as well as genetic susceptibility
• The fetus is most vulnerable for teratogens during the early development, when the major organs and structures of the body are forming. Each organ has a critical period during which it’s development can be disrupted. The type of congenital malformation produced by an exposure depends on which organ is most susceptible of the teratogenic exposure