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
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
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
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
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: process of cell death that is genetically programmed and is required for
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
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.
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
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.
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 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