Developmental psychology studies human development, the study starting not with the infant’s birth but before it, while it is in embryonic form within its mother’s womb. The child’s development within the womb is a very important phase of his entire development.
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Hence, there has been origination in the form of a fertilized ovum. Gradually and continually, this fertilized ovum shows signs of structural development; the ovum cells multiply in number and increase in size. These cells are of two kinds, the germ cells and the somatic cells.
The germ cells help the germ cell plasma to develop various physiological parts such as bones, muscles, nerves, etc. Beside changes in structure, the functions of the embryo also take on variety and complexity. Functional development occurs with the addition of new activities.
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While the human being is in the embryo, the structural and functional developments take place in the nature of two mutually supplementary aspects of total development.
Psychologists have divided the embryonic development of the being into several states. These states and a brief mention of them are given below:
1. Germinal Period
The period beginning with conception of the child and lasting for a period of two weeks is called the germinal period of the being’s development. During this period of the being exists in the form of a fertilized ovum, not being given any external nutrition. The form of the fertilized ovum is that of an egg, and its cells are equally divided.
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2. Embryonic Period
The period from the third to the eighteenth week of pregnancy is called the embryonic period, during which the embryo gets nutrition from its parent. As a result, its form undergoes rapid change. In the change there is a sac related to the ovum and it is situated between the cells that lie in between Amniotic sac and Yolk sac.
In this the cells lying next to the amniotic sac are called the ectoderm calls. The calls of the first kind prove of help in the development of the digestive and the respiratory systems, while the latter or second kind of cells lead to the development of the nervous system and the skin of epidermis. The mixing of the two kinds of cells leads to the development of a new layer called the mesoderm.
Development of the two kinds of cells leads to the creation of muscles and bones. Cell’s structure which is originally flat and convex gradually spread out. Every cell has its own peculiar position, and if it is changed, its characteristic features will also undergo some change.
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For example, if it would originally have developed into skin, it will develop into the muscles of the eye on changing the. Cells certain chemical substances are also of importance in the separate and individual development of the cells. These chemicals are called organizers. Besides these, the development of the embryo is influenced by the use of the light, electrical field, X-rays, and other chemical rays.
3. Fetal Period
In the development of the being, this state begins, with the eighth week, and in it a number of cells increase, following which their size improves. Change in this stage is very tepid.
As has been pointed out above, the child’s development during pregnancy is characterized by two types of development, the structural and functional the following two laws are accepted in respect of structural development:
(a) Law of Caphalocaudal Development
According to this law, in the development of the embryo, the development starts with the cephalic portion or the head and gradually proceeds to the tail portion. In this way, this law of development the direction of the bodily development. This law applies to growth as well as differentiation.
(b) Law of Proximo Development
According to this law, the progress in development is more rapid in peripheral parts, situated in the centre.
In structural development, the structure of the nervous system is a very important one. In this development, the first layer of the ectoderm cell turns inwards to form the neural tube, the major portion of which, the spinal cord and the upper part develops into the brain.
In the fifth week of development, the medulla, cerebellum and the mid-brain become distinctively visible. The nervous system develops very rapidly during the fetal period. Muscles, being to be formed even before the nerves and sensory organs almost all the sensory parts develop in the being before the delivery or actual birth.
The development of vision starts with the second week, and continues even after pregnancy. Receptors concerned with olfactory reach maturity in pregnancy in the case of some children. Taste cells develop in the third month that is during the fetal period. Besides this, during pregnancy the being attains the power of felling sensations of pressure on the skin.