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Chapter 5

Chapter 5 - The Child.docx

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University of Toronto Scarborough
Mark Schmuckler

The Childs Growth: Brain, Body, Motor Skills, and Sexual Maturation o There is enormous variation in the rates at which children develop, and girls usually develop more rapidly than boys. o Developmental neuropsychology is now in a position to usefully relate brain development to behavioral development o In the prenatal period, the brain grows very rapidly, and it continues to grow at an amazing pace Although at birth the infants brain only weighs about as much as a mature brain, by the time the baby is about 6 months old, his brain weights of what an adult brain weighs, and the brain of the 2 year old child weight 75% as much as an adult brain o Largest portion of brain consists of two connected hemispheres that make up the cerebrum, a mass of tissue that embodies not only attributes particular to humans such as speech and self-awareness attributes shred with other vertebrate animals such as sensory perception, motor abilities, and memory AS the brain develops, the front part expands to form the cerebrum the large, convoluted upper mass that in the adult dominates the upper and side portions of the brain. The cerebrum is covered by the cerebral cortex As human beings mature, male brains tend to be heavier than female brains because of mens larger body size none of these differences have differential effects on either genders intellectual abilities The covering layer of the human cerebrum, the cerebral cortex contains cells that control specific functions, such as seeing, hearing, moving, and thinking; convoluted and contains about 90% of the brains cell bodies Specific functions, such as seeing, hearing, moving, feeling emotions, thinking, and speaking, can be traced to specific regions of the cerebral cortex The cortex is divided into four lobes: frontal, temporal, parietal and occipital. Left hemisphere associated with the processing of language, whereas the right hemisphere plays a greater role in visual and spatial processing Because of the brains plasticity, functions lost due to damage to a hemisphere, lobe, or area may be compensated for by another brain region o At birth a babys brain has most of its neurons, or nerve cells 100 to 200 billion of them. In fact most neurons are present in the brain by the seventh month of gestation. Neuron is essentially a cell in the bodys nervous system, consisting of a cell body, a long projection called an axon, and several shorted projections called dendrites; neurons send and receive neural impulses, or messages, throughout the brain and nervous system During the embryonic period, neurons multiply ay a very rapid pace in a process called neuron proliferation: about 250,000 new neurons are born every minute Studies suggest that the adult brain has the capacity to regenerate nerve cells o Glial cells, which surround and protect neurons, also grow. These cells also provide neurons with structural support, regulate their nutrient, and repair neural tissue. Some glial cells are responsible for the important task of myelination, in which parts of neurons are covered with layers of a fatty, membranous wrapping called myelin. This insulating makes the neuron more efficient in transmitting information Most myelination occurs during the first two years of life The neurons axon terminates in synaptic knobs, which, in synaptic connection with the dendrites of another neuron or with other types of cells, transmit messages through the nervous system. The myelin sheaths that encase much of the axon facilitate the transmission of signals rapidly and efficiently. Neurons are the longest cells in the human body and may reach more than 3 feet in length. o Neurons are always on the move in the process of migrating to their final location. Guided by neurochemical processes, this neural migration ensures that all parts of the brain are served by a sufficient number of neurons. Absence of sufficient neurons associated with various form of mental disability and with disorders such as dyslexia and schizophrenia o Synapses, are a specialized site of intercellular communication where information is exchanged between nerve cells, usually by means of a chemical neurotransmitter These specialized junctions the extended axon of one neuron transmits a message to the projected dendrites of another neuron, usually by means of chemicals that cross the small space between the neurons Activity is crucial to survival and learning, for as the brains neurons receive input from the environment they create new synapses o Synaptogenesis, or the forming of synapses, begins early in prenatal life, as soon as neurons begin to evolve. The brain forms many more synapses than neurons; for example, at birth in the brains visual cortex alone, there are 2,500 synapses for every neuron When child is about 2 years old, there are about 15,000 synapses for every neuron The brain is programmed to create more nerve cells and more connections between these cells than are needed With development, two processes reduce the number of neurons and connecting fibers. When new synapses are formed, some surrounding neurons die in what is called neuronal death or programmed cell death apparently for more space for these crucial loci of information transmission. o In synaptic pruning, the brain disposes of a neurons axons and dendrites if that particular neuron is not often stimulated This frees up space for new synaptic connections. The goals of both neuronal death and synaptic pruning are to increase the speed, efficiency, and complexity of transmissions between neurons and to allow room for new connections that develop as the child encounters new experiences By adulthood, each of the brains approxiamately 1 trillion neurons makes 100 to 1,000 connections with other neurons = 1 qaudrillion synapses Across the small space between one neurons synaptic knobs and the dendrites or soma of another neuron, a chemical substance effects the transfer of information During childhood, the brain overproduces neuron connections, establishes the usefulness of certain ones of these, and then fine- tunes the extra connections. Especially in the frontal cortex, overproduction of synapses may be essential for infants to develop certain intellectual abilities. SUMMARIZE CHART HERE o When the infant is about 2 months old, motor reflexes, such as rooting and the startle response drop out, and the motor cortex begins to oversee voluntary movement, such as reaching, crawling, and walking In the visual cortex the number of synapses per neuron is multiplied some six times within the first two years of life o One of the most important organizing features of the brain is its left-right dividng into two halves or hemispheres. The right and left hemispheres, which are connected by a set of nerve fibres called the corpus callosum, are anatomically different and, in general, control different functions Since there is a great deal of cross-wiring occurring between the two hemispheres, the separation is by no means complete When one side of the brain suffers damage, the other half may take over some functions o Hemispheric specialization begins early in life and is the differential functioning of the two cerebral hemispheres; for example, the control of speech and language by the left hemisphere and of visual spatial processing by right The left hemisphere of the motor cortex controls simple movement in the right side of the body, and the right hemisphere controls the bodys left side. Lateralization describes the specialization of each hemisphere in specific perceptual and cognitive tasks The right hemisphere processes visual-spatial information, non-speech sounds like music, and the perception of faces When damage occurs to the right side of the brain, people may have difficulty attending to a task requiring visual-spatial perception, their drawing skills may deteriorate, they may have trouble following a map or recognizing friends, or they may become spatially disoriented Right hemisphere is also involved in processing emotional information, and one can have difficulty interpreting facial expressions Pell found that that individuals with both right-brain and left-brain damage
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