Age in months Age in years

Figure 83-8

Average height of boys and girls from infancy to 20 years of age.

Figure 83-9

Walks alone Stands alone Walks with support Pulls up Grasps Crawls

Sits briefly

Rolls over

Hand control Head control Vocalizes Smiles Suckles

Figure 83-9

Behavioral development of the infant during the first year of life.

Behavioral Growth

Behavioral growth is principally a problem of maturity of the nervous system. It is extremely difficult to dissociate maturity of the anatomical structures of the nervous system from maturity caused by training. Anatomical studies show that certain major tracts in the central nervous system are not completely myelinated until the end of the first year of life. For this reason, it is frequently stated that the nervous system is not fully functional at birth. The brain cortex and its associated functions, such as vision, seem to require several months after birth for final functional development to occur.

At birth, the infant brain mass is only 26 per cent of the adult brain mass and 55 per cent at 1 year, but it reaches almost adult proportions by the end of the second year. This is also associated with closure of the fontanels and sutures of the skull, which allows only 20 per cent additional growth of the brain beyond the first 2 years of life. Figure 83-9 shows a normal progress chart for the infant during the first year of life. Comparison of this chart with the baby's actual development is used for clinical assessment of mental and behavioral growth.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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