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Unformatted text preview: Chapter 4 I. GROWTH & STABILITY A. Rapid Physical Growth of Infancy : Birthweight has doubled to about 15 pounds in healthy infants by the age of 5 months, and by their first birthday, their weight has tripled to about 22 pounds. Weight gain slows during the second year of life, but progresses so that by 2-years-old, the child weighs about four times its birthweight. By the end of its first year of life, the average baby has grown almost a foot in length, to about 30 inches tall. By its second birthday, it will have grown to 36 inches on average. Major Principles That Govern Growth: cephalocaudal principle: the principle that growth follows a pattern that begins with the head and upper body parts, then proceeds down to the rest of the body. This is reflected in gestational physical growth, as well as in the development of neuromuscular strength and control. Cephalocaudal means "head-to-tail," and is how the zygote-embryo-fetus grows, and how we develop our abilities after we are born. For example, babies first lift their head, then use their arms, then lift their chest, then sit up, then eventually stand, then walk. proximodistal principle: the principle that development proceeds from the center of the body outward, it means, "near-to-far." For example, the trunk of the body develops before the arms and legs, which precede the hand and feet, which precede the fingers and toes. hierarchical integration: the principle that simple skills typically develop separately and independently but are later integrated into more complex skills. For example, learning to walk is a complex skill developed over time after many simpler skills are accomplished, such as sitting, crawling, standing, and walking while holding onto supports. principle of the independence of systems : the principle that different body systems grow at different rates. For example, sexual characteristics and speech development and muscle control all develop on their own time table. B. The Nervous System and Brain Neurons: these are the cells which make up the nervous system, and it is estimated that infants are born with between 100 and 200 billion neurons. We are actually born with more neurons than we need, since as far as we know so far, no or few new neurons grow after birth. There is an actual "pruning down" of the neurons we are born with. What basically happens is that neurons not interconnected in working neural networks used to survive are eliminated. This makes economic sense--why support superfluous cells with nutrients, water, and oxygen when they are serving no purpose, and there are working cells need those resources? This pruning down of unnecessary neurons increases the effectiveness and efficiency of the nervous system....
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This note was uploaded on 11/16/2011 for the course PSYCH 106 taught by Professor Koch during the Spring '11 term at Kennesaw.
- Spring '11