DEVELOPMENT OF THE NERVOUS SYSTEM:Operation Head Start

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Neurological Basis of Behavior (PSY - 610)

Lesson17

DEVELOPMENT OF THE NERVOUS SYSTEM

Objective

To familiarize the students with:

· Development of the brain: from the fertilization to the various developmental stages in-utero,

and postnatal. Cell migration, ( inside-out), cell competition, Cell death, growth Cones, Nerve

growth Factor and its role

· Various stages of neuronal development.

· Teratogenesis Genetic anomalies which affect development of the brain. Plasticity of the

Nervous system.

· Development and growth (from intrauterine to neonate stages) to give an understanding of the

stages of development and the processes involved.

Development of the brain

Before we study the development of the brain it is important to understand life before birth

The process begins with the fertilization of the egg, and once fertilized this is known as a zygote. The

zygote undergoes rapid cell division and Mitosis is the process of cell division by which zygote grows

Zygote: After fertilization, fertilized and rapidly growing, enlarged egg travels towards the

uterus in 1st two weeks, after reaching the destination; it attaches itself to the uterus walls with

its tendrils. This is a very important linkage as it provides nurturance and nutrition which is

required for rapid growth of the zygote. This process of attachment is known as Implantation.

Embryo: After the successful implantation in the uterus, immense and rapid growth takes

place. This is when the embryo starts resembling human form. The amniotic sac ("bag"}

created, it is filled with amniotic fluid which protects the embryo and provides constant

temperature within the sac. The embryo is connected to the mothers systems and is dependent

on the mother through umbilical cord. Placenta is the container in which the embryo is

contained and attached to the mother. The double walled cavities of the placenta provides

support, nurturance (nutrients) needed by the embryo. This forms the placental barrier which

protects the embryo form harm and toxics.

Fetus: After four months of life after fertilization, the embryo develops into the fetus which is

the next stage. Now an individual with Reflexes which can be seen. The suckling and

swallowing develop halfway through the prenatal period. We also know that internal and

external stimulation affects are responded to by movements. So now we have a fetus

responsive to the environment (within the placenta).

Differentiation takes place in the germinal layers and then rapid division and multiplication of the

germinal cell layers into different types of cells takes place during these stages. The form shape and

development of the body and brain takes place following the principle of growth:

Operation Head Start. The brain and body grows in the cephalo-caudal (head to tail principle). This

means the development of the head and the brain if the first stage.

If we look at the reflexes of the neonate we see a very well documented development and progression

(of the brain and the body):

Neurological Basis of Behavior (PSY - 610)

Reflexes of the neonate

Plantar: if we stroke foot of the neonate the toes fan up and out

Rooting: If a cheek is softly touched, the newborn turns mouth towards the cheek which has been

touched.

Suckling: if an object is placed in the mouth, the newborn starts sucking placed in mouth. This is

readiness for feeding.

Moro responses: if there is a sudden noise the newborn stretches out at first then hugs itself together.

Grasping: If a round object or finger is placed against the fingers, the fingers curls around finger or rod

placed. The curling forms a very strong grip.

Other reflexes: Swimming, (remember they have been swimming through out the first 9 months in-

utero), vomiting, hiccough, sneezing, yawning, blinking normally occurs within an hour after birth.

References

1. Brown, T.S. and Wallace. (1980) P.M Physiological Psychology

Academic Press New York

2. Kalat J.W (1998) Biological Psychology Brooks/ Cole Publishing

3. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

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