Test 2 Study Guide Chapter 4 By the end of the first year of post natal life the average American child weighs about 20 pounds and is about 30 inches long o More than double the weight at birth Physical Growth o Easy to observe and quantify o Tells us a lot about whether a child is developing normally o General Principles of Physical Growth Directionality how body proportions change Generally change is cephalocaudal from head to tail o Ex eyes mature earlier than the legs Could also be proximodistal progresses from the center out o Ex prenatally the heart begins to beat before the fingers are o Ex postnatally the child can control large arm movement developed before finer hand ones Independence of Systems states that different parts of the body develop along different timetables Ex by the time an infant is 2 years old the nervous system has reached more than half its mature form whereas secondary sexual characteristics don t appear until puberty Canalization development tends to follow and return to a normative course Many systems of the body are genetically programmed to follow a standard and highly structured course of development If something throws development off course genetic forces make a correction as soon as possible like playing catch up o Catch up also occurs in cognitive development o Norms and Individual Developments In studying physical development scientists consider both norms and individual differences Norms average outcomes on some characteristic Individual differences variation among individuals on some characteristic Development can follow many different paths to the same or different ends Infants born in richer countries tend to be healthier heavier and longer than infants born in poorer countries Within wealthier countries infants born into poverty grow more slowly and do not reach equivalent levels of height or weight as those born in prosperity The Development of the Central Nervous System o CNS the division of the nervous system that consists of the brain and spinal cord processes information and directs behavior o Connections between the brain and behavior are bidirectional Genetically predetermined brain development makes new behaviors possible which lead to interactions with the environments causing brain development o The brain CNS begins as a layer of cells on the outer surface of the embryo and is already visible one month after conception Subcortical structures brain components that control state of arousal First to emerge in development Limbic system part of the nervous system that manages emotions Develops second Cortex thin layers of outer tissue that cover the brain and association areas parts of the brain concerned with awareness attention memory and the integration of information emerge last Cortex contains 75 of the brain s cells Brain divided into two hemispheres halves which are connected by the corpus collosum Does not complete growth until 6 years of age Does not fully mature until adolescence Different areas of the brain have specialized functions Visual cortex sight Auditory cortex hearing Sensorimotor cortex touch Motor cortex voluntary movement Frontal cortex command center thinking planning initiative impulse control creativity Wernicke s area language comprehension Broca s area language production speech o Brain cells Your brain contains approximately 100 billion cells Neurons cells that carry information across the body and brain as well as back and forth within the brain Compose grey matter Three main parts o Dendrites branched extensions of a neuron that act like antennas that pick up signals from other neurons o Cell body part of the cell that contains the nucleus and biochemical mechanisms to keep the cell alive and determine whether the cell will fire o Axon carries signals away from the cell body toward other neurons Divide into axon terminals at the tips Synapse connection between one neuron s axon and another s dendrite o Miniscule gap Neurotransmitters electrochemicals through which neurons intercommunicate Action potential an electrical charge inside the neuron By about the 6th month of gestation cell birth and migration within the brain are more or less complete At birth the brain is about the size of an adult brain and virtually all of the neurons that will ever exist are in place Dendrite synapses and axons are still developing Synaptogenesis a key process in brain development in which connections develop between neurons through the growth of axons and dendrites 100 000 new synapses form every second in the first 6 months of life Rate peaks at about age 1 and slows down in early childhood Continues throughout life as we learn new skills acquire knowledge build memories and adapt to changing circumstances Synaptic pruning the process of elimination of unused and unnecessary synapses Almost twice as many synapses at birth than in adulthood If it does not occur the child s dendrites are too dense and too long causing mental retardation and other developmental disorders Plasticity the capacity of the brain to be modified by experience Fundamentals Synaptogenesis and synaptic pruning Myelination the process of covering the axons with myelin a white fatty tissue Increases the speed of neural impulses Improves information transmission between cells Begins prenatally and is ongoing throughout adulthood Brain s white matter Fibers that connect the cerebellum balance control of movements to the cerebral cortex grow and myelinate through age 4 o Advances in motor control Multiple sclerosis a disease in which the autoimmune system strips neurons of myelin leading to loss of motor control deteriorating speech and vision and sometimes death in early adulthood Transmission of information among cells is at first diffuse spread out so that reactions to stimulation develop and end slowly More orderly when more developed creates a phasic reaction that is locked in time with stimulation and is much more specific Experience smoothes connections among cells to improve perceptual pathways Maturation and experience play key roles o Cell activity Microelectrode recording a technique used to measure the activity of individual Individual cells have highly specialized functions cells Developed by Hubel Brain prewired in ways that assist visual perceptions Electroencephalographic EEG recordings measurements acquired with sensors at the scalp that show electrical activity of masses on individual cells Sensors placed on the scalp to pick up