Chapter 2: The nevous system (Structure and Function)
Prenatal development: all the steps involved with the formation of the various
structures and functions of the body, and for our purpose, specifically of the
Improper nutrition may lead to physiological difficulties later in life such as
obesity and problems in programming he appetite regulatory system correctly in
the developing fetus.
Proper nutrition is critical for the development of an intact nervous system.
Fetal alcohol syndrome can cause serious cognitive difficulties, is related to
In Canada, 1 out of 300 live births was affected and that fetal alcohol disorders
were the leading cause of neurologically based developmental disabilities about
Canadian children and youth.
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 prolong stress.
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: Pneumonia, bronchitis or other serious systemic infections.
Physical abuse: episodes of abusive behavior which result in physical injury to a
May lead to brain impairment to the baby especially if she is struck in the
Shaken baby syndrome: may result from physical abuse and can lead to traumatic
Emotional abuse: an individual is verbally made to feel bad about him or herself
Development of the Central Nervous System:
Dorsal(superior) – toward the back or toward the top of the brain;
Ventral (inferior) – Toward the belly or the bottom of the brain;
Rostal (anterior) – toward the head
Caudal (posterior) – toward the rear or away from the head
The period from the time of conception to approx. 2 weeks later when
implantation in the uterine wall occurs is termed the germinal period.
The developing cells are called zygote.
A mass of cells with a fluid center has formed which is called the blastocyst.
The blastocyst implants on the uterus wall.
The blastocyst consists of the inner tissue, which will become the embryo, and to
the trophyblast: provide nutrition.
Once this occurs, it is now considered an embryo.
The embryo then differentiates into 3 distinct layers.
The ectoderm is the outermost of the three layers of the embryo which develops
into the skin, sense organs, and nervous system. The mesoderm is the middle layer and becomes the muscle, blood and excretory
The endoderm is the innermost layer and becomes the digestive system, lungs
and other internal organs.
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: 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
The next development is the beginning of the nervous system.
The first recognizable structure during nervous system development is the neural
Neural plate begins to become evident at approx.. 3 weeks of age and appears to
be induced by signals from the mesoderm layer.
As time progresses, the neural plate folds to form the neural groove.
The lips of the neural groove fruse to form the neural tube by approx.. the 24
day after conception.
The inside of the neural tube becomes the spinal canal and the cerebral ventricles.
The swellings at the end of the neural tube develop into the forebrain, midbrain
and the hindbrain.
At the end of 7 weeks, the embryo is referred to as the fetus which has begun to
resemble a more human shape.
Although it seems to be very short time, the brain is almost a complete replica of
the adult brain at approx. 100 days from time of conception.
Neural crest is dorsal to the neural tube.
Neural crest cells develop into the neurons and glial cells of the peripheral
Glial cells appear in many parts of the body as development continues.
Prenatal Neuronal Development:
How do neurons develop?
There are several stages: induction, proliferation (neurgensis), migration and
aggregation, differentiation, axonal growth and synaptic formation
(maturation), programmed cell death (apoptosis), and synaptic
Induction begins when part of the ectoderm becomes the nervous system.
This occurs during the development of the neural plate.
Stem cells: able to develop into different types of cells and have an almost
unlimited capacity for selfrenewal.
As the stages progress, the cells become more specific which leads to more
specialized cell function.
Proliferation is a term used to describe a time of immense cellular division, which
occurs once the neural tube is formed. 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 they migrate they to their appropriate place, the follow chemical pathways
that help to lead them to the correct area or location.
Once cells have migrated they begin to aggregate.
Aggregate means they move toward other cells that have migrated to similar area
to form nervous system structures.
After aggregation comes a time of axonal, dendritic, and synaptic formation also
Once the primitive neuron reaches its specific location, the process of maturation
will give the neuron its entire distinguishing factures.
At the 12 week, the brain starts to assume more of a concrete model of the adult