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Chapter 5

Chapter 5

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Western University
Psychology 2040A/B

Psych 2040A Chapter 5: Physical Development: The brain, body, motor skills, and sexual development An Overview of Maturation and Growth growth and physical development includes external and internal changes Changes in Height and Weight babies grow rapidly in the rst 2 years, often doubling their birth weight by 4-6 months of age and tripling it by the end of rst year by age 2, toddlers are already half their adult height and have quadrupled their birth weight physical growth and development are most obvious during puberty, where people go through a 2-3 year growth spurt Changes in Body Proportions the newborns head is already 70% of its eventual adult size and represents one quarter of the total body length, the same fraction as legs development proceeds in a cephalocaudal fashion - a sequence of physical maturation and growth that proceeds from the head (cephalic region) to the tail (caudal region) - development proceeding head down trunk and legs growth the fastest for children when children grow upward, they are also growing outward - proximodistal development - a sequence of physical maturation and growth that proceeds from the centre of the body (the proximal region) to the extremities (distal regions) internal organs form rst in a fetus before the extremities Skeletal Development skeletal structures that form during prenatal development are soft cartilage that will gradually ossify (harden) into bone newborns bones are soft, pliable, and difcult to break the neonates skull consists of several soft bones that can be compressed to allow the child to pass through the cervix and the birth canal one method of estimating a childs level of physical maturation is to x-ray the wrist and hand skeletal age: a measure of physical maturation based on the childs level of skeletal development x-ray shows number of bones and extent of ossication girls mature faster than boys - at birth, girl are only 4 to 6 weeks ahead in skeletal development, but by age 12, the gender difference has widened to 2 full years. skeletal development is usually completed by age 18 Muscular Development neonates are born will all the muscle bres they will ever have at birth, muscle tissue is 35% water and it accounts for no more than 18 to 24 percent of a babys body weight muscular development proceeds in cephacaudal and proximodistal directions, with muscles in the head and neck maturing before those in the trunk and limbs increase in muscle mass are more dramatic for boys Variations in Physical Development physical development is a very uneven process in which different bodily systems display unique growth patterns - brain and head actually grow much faster and are quicker to reach adult proportions than the rest of the body Individual Variations individual differences in the rate of maturation not only result in visible differences in physical features such as height, but also contribute to differences in other areas of development, such as cognition faster processing speed was found in early maturers, especially boys Cultural Variations people from Asia, South America, and Africa tend to be smaller than North Americans there are cultural differences in the rate of physical growth Asian ad African-American children mature faster than European or European-American children Development of the Brain the brain grows very early in life, reaching 75% of its weight by age 2 brain growth spurt: the period between the 7th prenatal month and 2 years of age when more than half of the childs eventual brain weight is added brain increases about 1.7g per day Neural Development and Plasticity synapses: the connective space (juncture) between one neuron and another neurons: nerve cells that receive and transmit neural impulses basic units of the nervous system neurons are produced in the neural tube of the embryo the majority of the neurons a person will ever have are developed by the end of the 2nd trimester of pregnancy, before the brain growth spurt however, scientists have established that formation of new neurons in the hippocampus occurs throughout life glia: nerve cells that nourish neurons and encase them in insulating sheaths of myelin they continue to form throughout life, unlike neurons Cell Differentiation and Synaptogenesis neurons assume specialized functions (ie. hearing, vision, smell, etc) once they migrate to a specic area of the brain individual neurons have the potential to serve any neural function, and the function each serves depends on where it ends up synaptogenesis: formation of connections, synapses, among neurons this proceeds rapidly during the brain growth spurt the average infant has far more neurons and neural connections than do adults reason is the neurons that successfully interconnect with other neurons crowd out those that dont, so that about half of the neurons produced in early life also die in early life.plasticity: capacity or change; a developmental state that has the potential to be shaped by experience brain has produced excess neurons and synapses in preparation for receiving any and all kinds of sensory and motor information a human being can experience synaptic pruning: surviving neurons that are stimulated less often loose their synapses and stand in reserve to compensate for brain injuries or to support new skills The Role of Experience Austin Reisen and his colleages did a study on chimpanzees - infant chimpanzees that were reared in the dark for periods ranging up to 16 months dark-reared chimpanzees experienced atrophy of the retina and the neurons that make up the optic nerve this atrophy is reversible if the animals visual deprivation did not exceed 7 months animals raised with lots of companions and many toys to play with have brains that are heavier and display more extensive networks of neural connections Brain Differentiation and Growth at birth, the most highly developed brain areas are the subcortical (lower) brain areas rst areas of the cerebrum to mature are the primary motor areas and the primary sensory areas Myelinization myelin sheath acts like an insulator to speed the transmission of neural
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