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Chapter 2

PSYC32H3 Chapter Notes - Chapter 2: Neocortex, Homeostasis, Red Nucleus

Course Code
Zachariah Campbell

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PSYC31H3 Week 1 Notes on Chapter 2
Prenatal Development:
External Factors:
Prenatal Development refers to all of the steps involved with the formation of the
various structures and functions of the body and, for our purpose, specifically of
the central nervous system.
Many fetal difficulties such as low birth weight and smaller head circumference
may be caused by malnutrition. Improper nutrition may also lead to other
physiological difficulties later in life such as obesity and problems in programming
the appetite regulatory system correctly in the developing fetus.
Abstaining from alcohol and other drugs, decreasing stress level, and avoiding
physical or emotional abuse are also desirable for the proper formation of the
central nervous system. Alcohol and various other drugs which cross the
placental barrier can directly affect the fetus. Fetal alcohol syndrome, which
can cause serious cognitive difficulties, is directly related to alcohol consumption.
Studies have shown that increased stress levels raise the amount of cortisol in
the body. Cortisol is a steroid hormone released by the adrenal cortex which
elevates blood sugar and metabolism and helps the body adapt to prolonged
stress. However, excess cortisol for too long a period of time may lead to the
depression of the immune system and leave the individual vulnerable to various
illnesses. Examples of illnesses that could affect a compromised immune system
include pneumonia, bronchitis, or other serious systemic infections.
Severe physical abuse to the mother may lead to brain impairment in the baby
especially is she is struck in the stomach. Shaken baby syndrome may result
from physical abuse and can lead to traumatic brain injury. In cases of shaken
baby syndrome, the infant is shaken so hard that his or her brain impacts the
skull in a manner similar to the effects of a motor vehicle accident.
Emotional Abuse is further form of abuse in which an individual is verbally made
to feel bad about him- or herself and abilities. Emotional abuse to the mother
may lead her to neglect herself and fail to care for her physical needs. Lack of
care of the mother while pregnant could greatly affect the child and also cause
neglect of any other children.
Development of the Central Nervous System:
When the sperm and egg unite, the process of cell division initiates very quickly.
The period from the time of conception to approximately 2 weeks later when
implantation in the uterine wall occurs is termed the germinal period.

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The developing cells are called a zygote.
By the end of the 1st week, a mass of cells with a fluid center has formed which is
called the blastocyst. The blastocyst enters the uterus and by the 11th-15th day
following conception, the blastocyst implants on the uterine wall.
The blastocyst consists of the inner tissue which will become the embryo, and
the trophoblast.
Once implantation occurs, it is now considered an embryo.
The embryonic stage lasts until the end of the first trimester. The growth of cells
is fairly rapid. The embryo then begins to differentiate into three distinct layers.
The ectoderm is the outermost of three layers of the embryo which
develops into the skin, sense organs, and nervous system.
The mesoderm is the middle layer and becomes the muscles, blood, and
excretory system.
The endoderm is the innermost layer and becomes the digestive system,
lungs, and other internal organs.
In addition to the cell layers, the life support system for the embryo
develops simultaneously.
The amnion is a sack of fluid in which the embryo floats for temperature
regulation and protection.
The umbilical cord connects the embryo to the placenta. The placenta is a
group of tissues in which blood vessels from the embryo and mother mix but do
not join. Very small particles cross from the mother’s blood to the embryo, such
as water, salt, and oxygen, while carbon dioxide and waste from the baby return
to the mother.
The first recognizable structure during the nervous system development is the
neural plate made up of the ectodermal tissue on the dorsal surface of the
developing embryo. The neural plate begins to become evident at approximately
3 weeks of age and appears to be induced by signals from the mesoderm layer.
At the time the neural plate becomes evident the cells are totipotent or able to
become any cell in the body. As the neural plate develops, the cells begin to lose
their ability to form into any type of tissue making them specific to central nervous
system development.
As time progresses, the neural plate folds to form the neural groove. The lips of
the neural grove fuse to form the neural tube by approximately the 24th day after
conception. The inside of the neural tube becomes the spinal canal and the
cerebral ventricles.

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The swelling at the end of the neural tube develop into the forebrain, midbrain,
and hindbrain.
The central nervous system changes greatly in the first 7 weeks of development.
By the end of these 7 weeks, the embryo is referred to as the fetus which has
begun to resemble a more human shape. Although it appears to be a very short
period of time, the brain is almost a complete replica of the adult brain at
approximately 100 days from the time of conception, although the structures are
not completely developed.
The neural crest is dorsal to the neural tube. It is formed from cells that
differentiate from the neural tube as it is being formed. Neural crest cells develop
into the neurons and glial cells of the peripheral nervous system. Glial cells
appear in many parts of the body as development continues. They colonize at
specific locations such as the gastrointestinal tract where they help to continue
formation of both the central nervous system and the peripheral nervous system.
Prenatal Neuronal Development:
Most researchers divide the process into several stages: induction, proliferation
(neurogenesis), migration and aggregation, differentiation, axonal growth and
synaptic formation (maturation), programmed cell death (apoptosis), and synaptic
The process of induction begins when part of the ectoderm becomes the
nervous system. This occurs during the development of the neuronal plate. Cells
at this point are described as totipotent. Another name for these cells is
multipotent because the embryonic neural crest tissue tends to give rise to many
cells that are highly specific later in the adult’s life, a unique quality of
In modern neuropsychology these cells are most commonly termed stem cells,
because they are able to develop into different types of cells and have almost
unlimited capacity for self-renewal.
Proliferation is a term used to describe a time of immense cellular division,
which occurs once the neural tube is formed. It is also termed neurogenesis
because it is the beginning of the development of neurons and occurs for the first
5 months of gestation.
Cell migration begins after the first neurons are developed and continues
several weeks after neurogenesis is complete. As these cells migrate to the
appropriate place, they follow chemical pathways that help to lead them to the
correct area or location.
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