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no plagiarize, spell check, and check your grammar. Please only use the attached chapter 5

I think of the weaknesses of this theory is that certain assumptions of health and the extent and degree of any insult to the brain are taken via history rather than direct examination. Unfortunately, no 2 brains are alike and hence the influence of the environment can vary between individuals so just understanding how and what kind of conditions the child was subjected to can only give us a clue not a definitive answer on exactly what has happened to the brain.

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5 Physical Development: Brain and Body iStock/Thinkstock Learning Objectives After completing this chapter, you should be able to: • Detail the process of nerve function and course of brain development through the lifespan. • Identify patterns of physical growth and change. • Outline major milestones in motor development. • Specify the physical signs of aging during adulthood, and distinguish between primary and secondary aging. • Describe the role of touch in psychosocial development. • Explain how our sense of smell and taste develop and change. • Compare the onset and consequences of various types of hearing loss. • Outline age-related developments in the visual system. 135 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 135 2/11/16 8:24 AM Prologue Chapter Outline Prologue 5.1 Nervous System Development Neurons and Synaptic Development Timing of Growth The Adaptive Brain The Adolescent Brain The Mature Brain 5.2 Patterns of Physical Growth Weight and Height in Early Childhood Adolescent Growth Spurt Maximum Height and Diminishing Stature 5.3 Motor Development and Decline Development in Infancy and Childhood Development in Adolescence Changes in Adulthood Sex Differences in Motor Development Physical Norms and Cultural Variations 5.4 Physical Aging in Adulthood Programmed Theories of Aging Damage Theories Signs of Aging 5.5 Sensation and Perception: Touch, Smell, and Taste Touch Smell and Taste 5.6 Sensation and Perception: Hearing Development of Hearing Changes in Hearing 5.7 Sensation and Perception: Vision Visions in Infancy and Childhood Vision in Adulthood Summary & Resources Prologue When my son Max was 3 years old he could consistently hit a plastic baseball onto the tall roof of his grandparents’ house. He could throw and catch better than any kid his age. It was easy to see that he had terrific hand-eye coordination and would excel in the sport. By high school, however, despite being an outstanding athlete who excelled at basketball, soccer, and other sports, Max could not have lasted a day on the baseball team. 136 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 136 2/11/16 8:24 AM Section 5.1 Nervous System Development What could have accounted for the change? The answer is related brain and body development. For Max, genetics and brain maturation led to exceptional hand-eye coordination at a very early age; his use of muscles that facilitated growth of baseball skills supported increased brain expansion in the areas best suited for that sport. Then, for a number of reasons, it gradually became more and more difficult for Max to find opportunities to play baseball and he became interested in other physical activities, especially basketball. Because of plasticity, his brain began to accommodate basketball skills that the environment was dictating and (literally) pruned areas involved in baseball skills that were no longer being stimulated as before. The question remains whether brain activity stimulated basketball movements or if basketball movements stimulated brain growth—or maybe there is a reciprocal interaction we don’t yet understand. Throughout the lifespan, hormonal, neuronal, and physical changes of the brain and body are unquestionably governed by programmed genes. However, as you learned with regards to critical and sensitive periods, the environment can have a profound effect on developmental trajectories. In this chapter, we will focus more on the first part of the brain and body question and explore the universal aspects of biological and physical growth. In the chapter that follows, we will account for more individual factors that affect health and physical growth and decline. 5.1 Nervous System Development Every physical and mental action originates with the nervous system. Without it, we would not be able to engage in any processes that define us as human. The mature nervous system consists of the brain and spinal cord, designated the central nervous system (CNS), and neural tissues in the peripheral nervous system that extend away from the CNS into every other part of the body (see Figure 5.1). Beginning with a simple tube reminiscent of brains from primitive organisms, in a short time the human nervous system becomes extraordinarily complex. Neural development in humans begins when gastrulation occurs in the third week of gestation (see Chapter 3). The mesoderm sends signaling molecules to the ectoderm, which responds by forming the neural plate. This strip of neuronal stem cells will eventually configure the entire nervous system. From the neural plate, stem cells migrate and are involved in specific areas of neural circuit generation. The neural plate begins to fold and form grooves, forming the neural tube. By the end of week four, there are distinct areas that will later form the hindbrain, the midbrain, and the forebrain. These structures will form secondary structures by the end of week 7. The optical vesicle also appears during the fourth week, which will later form the eye and the optic nerve. Part of cell differentiation is dependent on proximity to the neural plate and how the cells become genetically programmed. Initial cell differentiation is expressed independent of experience, as the human genome directs the process. That is, cells are guided by genetic programming to become parts of various systems. Once cells reach their intended destinations, neural activity and experiences become a larger factor in determining emerging neural pathways (Cooper, 2013). The production of functioning neurons commences around post-conception day 42 and will continue for approximately 120 days (Stiles & Jernigan, 2010). 137 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 137 2/11/16 8:24 AM Section 5.1 Nervous System Development Figure 5.1: The nervous system The nervous system has two divisions: the central nervous system (the brain and spinal cord) and the peripheral nervous system (all of the nervous tissue located outside the brain and spinal cord). Brain Spinal cord Central nervous system Nerves of peripheral nervous system By the end of the first trimester, the fetus will display reflexes. It has also released the hormones that will determine the outward appearance of genitalia. The outer surface of the brain is still relatively smooth, and lacks visible gyri (ridges) and sulci (depressions). These will develop rapidly during the second trimester (Figure 5.2). Their convolutions allow for greater surface area and are probably the reason human brains are more advanced than any other species (Zilles, Palomero-Gallagher, & Amunts, 2013). However, the absolute number of brain cells is thought to be a factor in relative mammalian intelligence as well (Roth & Dicke, 2005). 138 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 138 2/11/16 8:24 AM Section 5.1 Nervous System Development Figure 5.2: Major regions of the mature brain The midbrain, hindbrain, and forebrain (shown here in a mature brain) begin to appear during week four of development. The gyri and sulci (singular gyrus and sulcus) refer to the ridges and depressions of the brain. Forebrain Hindbrain Midbrain During the second trimester additional structures mature and cells continue to be formed. By the end of this period, almost all neurons have been created but are yet to develop most of the connections that occur during the lifespan. Because most of the cells have been generated and structures are in place, the third trimester focuses on further sophistication of structures and systems. Neurons and Synaptic Development As is mentioned earlier in this section, the framework for the nervous system begins to form around day 14 of gestation, but its basic building block, the neuron, does not begin development until day 42. There are at least 100 billion neurons in the human brain. Although neurons come in many shapes and sizes, they have a number of common features. Unlike other cells, neurons communicate with each other in an elaborate electrochemical relay system. As depicted in Figure 5.3, information is first transmitted by dendrites, structures that receive incoming signals. The message then travels to the soma (cell body). If the signal is to be continued, it travels via the axon. The transmission may be sped up by a myelin sheath, which provides electrical insulation and eventually covers most of the long, threadlike axons. Unmyelinated fibers conduct impulses in a wave-like, energy intensive, sequential fashion. After myelination (the process of forming the sheath around the nerve), the axon is only exposed at regular gaps in the sheath, called the nodes of Ranvier. The electrical impulse cannot flow through the myelin, so it “jumps” to the next node, which might be a millimeter or more away (Morell & Quarles, 1999). This process speeds transmission of impulses and also saves energy since less surface area of the axonal membrane is used. Therefore, myelination is an important advance, as faster neural processing is necessary to move faster physically and to think in more complex ways. 139 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 139 2/11/16 8:24 AM Section 5.1 Nervous System Development Figure 5.3: The neuron The neuron is the basic element of the nervous system. Information is first received by the dendrites. The message travels to the cell body (soma). If the message is to be continued, it travels through the axon. Transmission speed is increased when the axon is covered in myelin, which allows the electrical transmission to “jump” from node to node. At the terminal buttons, neurotransmitters are released into the synapse between the sending and receiving neurons. Nucleus Dendrite Myelin sheath Axon Node of ranvier Terminal buttons The timing of myelination is governed by maturation. The myelination of sensory and motor neurons that are essential to early physical development is mostly complete by 40 months, whereas the neurons that are responsible for higher brain functions like reasoning and complex decision making are not myelinated until early adulthood. When experiences are limited, brain growth is similarly restricted. Compared to infants with richer experiences, those raised in less stimulating environments show significant brain differences in structure, weight, and volume (Lawson, Duda, Avants, Wu, & Farah, 2013; Luby, 2015). Not surprisingly, poor nutrition leads to less myelin development and a general reduction in brain size, though early treatment can often reverse these negative effects (Atalabi, Lagunju, Tongo, & Akinyinka, 2010; El-Sherif, Babrs, & Ismail, 2012; Gladstone et al., 2014). 140 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 140 2/11/16 8:24 AM Section 5.1 Nervous System Development Whether myelinated or not, neurons transmit electrochemical impulses to neighboring neurons (or glands or muscle fibers) at bulblike structures called terminal buttons. This transmission is achieved without the neurons actually touching each other. Instead, they form a synapse, or gap between the sending and receiving neurons. Every terminal button contains vesicles that release chemicals called neurotransmitters into the synapse (see Figure 5.4). Depending on a number of factors, especially the concentration of the specific neurotransmitter, the receiving neuron will either carry the message forward or not (the “all-or-none” principle). That is why sometimes people can perceive a faint sound or a distant light while at other times they cannot. The chemical messengers have either reached a particular threshold to transmit the sensory information or not. Figure 5.4: Neural transmission These neighboring neurons are able to share information using a complex process that involves transferring information as an electrical impulse within the sending neuron and as a chemical message between neurons. Dendrites Presynaptic neuron Axon Neural impulse Postsynaptic neuron Presynaptic neuron Axon Neural impulse Synaptic vesicles Presynaptic membrane Axon terminal Receptor site Postsynaptic membrane Synaptic cleft Neurotransmitter molecule Postsynaptic neuron 141 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 141 2/11/16 8:24 AM Section 5.1 Nervous System Development Timing of Growth At birth the infant brain weighs only about 25% of its adult weight, though the head is proportionately closer to adult size than other body parts; because of increased mass, by 2 years old the weight of the brain will have tripled. A popular theory to explain the rapid postnatal brain growth is based in evolution. Natural selection promoted a large and more sophisticated brain while also providing advantage to an upright gait. The vertical posture changed the position of the pelvis and made for a narrower birth canal that limited fetal brain growth. Therefore, in order to have a large, sophisticated brain, it would need to continue growing after exiting the relatively small birth canal. So instead of a brain that is mostly developed in the womb to allow locomotion and other tasks immediately after birth (like other mammals), humans have relatively undeveloped brains that continue to need plenty of attention. Variations in synaptogenesis (synaptic growth) correspond to sensitive periods in brain development. Therefore, the rate and timing of synapse and dendrite formation are important to understanding development (Tierney & Nelson, 2009; Twardosz, 2012). At birth, the vast majority of synapses have yet to form, setting the stage for explosive growth. As a new object is seen, a new sound is heard, or a new movement is made, neurons branch and extend their reach to other neurons and form new synapses. Although synaptic development initially unfolds by genetic programming (maturation), experience dictates which synapses receive the most stimulation and make the most connections. Although active changes in the brain are especially noticeable for the first 20 years or more, postnatal brain development is particularly concentrated during infancy and early childhood (Kolb, 2009). In just a few years, children become able to think, use language, practice most of the physical skills they will use as adults, and learn social behaviors that will aid their survival. When brain development peaks, as many as 250,000 neurons are born every minute; by the time a child is 2 years old, some cells may have up to 10,000 connections (Kolb & Gibb, 2011). Note in Figure 5.5 that synapses in the visual cortex that are responsible for sight reach peak production between the 4th and 8th postnatal months. Synapses in the more sophisticated reasoning centers of the prefrontal cortex do not peak until the 15th month; growth in language areas peaks just before infants begin to speak. Later, reasoning centers in the prefrontal cortex do not reach maturity until early adulthood. In total, our 100 billion neurons establish trillions of synapses, forming a complex yet integrated communication network. If stimulation is lacking during sensitive periods of brain development, prospects for growth, including psychosocial processes, fine and gross motor behavior, and language, can become limited (Gladstone et al., 2014; Vandersmissen & Peeters, 2015). Therefore, children must be given opportunities for new experiences and shielded from negative environmental effects like malnutrition. 142 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 142 2/11/16 8:24 AM Section 5.1 Nervous System Development Figure 5.5: Timing of synapse and dendrite formation The rate and timing of synapse and dendrite formation vary by age and are important to understanding development. Notice, for example, that growth in language areas peaks just before infants begin to speak. Angular gyrus/Broca’s area (language areas/speech production) Visual/auditory cortex (seeing and hearing) Relative growth Prefrontal cortex (higher cognitive functions) -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Age in months Age in years Source: From R. A. Thompson and C. A. Nelson, “Developmental science and the media: Early brain development,” American Psychologist, 56(1): 5–15. Copyright . 2001. Reprinted by permission of the American Psychological Association. The Adaptive Brain Rate and timing of physical growth in the brain also allows us to better understand the relationship between sensitive periods and neuroplasticity (the ability of the brain to adapt to experience). The younger the brain, the more “uncommitted” areas there are for neuroplasticity to operate. Sometimes another part of the brain will assume functioning; other times, functioning cells migrate to damaged areas. (In the adult brain, much of the research in the treatment of neurodegenerative disorders like spinal cord injuries and Alzheimer’s disease focuses on this knowledge that certain stem cells can become integrated into existing circuits [Lindvall & Kokaia, 2010; Obernier, Tong, & Alvarez-Buylla, 2014]). 143 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 143 2/11/16 8:24 AM Section 5.1 Nervous System Development To facilitate neuroplasticity during early brain development, there is a massive overproduction of synapses during infancy (as shown in Figure 5.6) before engaging in a process of reduction, called synaptic pruning, in order to create an individual network of connections for each person. This principle of “use it or lose it” serves as a biological foundation for learning, as mentioned in the prologue. Pruning is natural and desirable because brain efficiency improves and behaves adaptively. This favoritism allows neurons that receive the most stimulation—and thus are interpreted as the most important—to be given space to grow more elaborate connections. Like synapse formation, timing of pruning varies depending on brain areas. In some instances, pruning is not complete until adolescence or beyond (Selemon, 2013). Not only does the brain adapt to stimulation, but if a part of the brain is damaged before it has begun its major synaptic growth, other cells can take the place of those that are damaged. For example, researchers have surgically removed brain parts of one-day old ferrets that are essential to hearing. Neural pathways that would otherwise have been eliminated through pruning replaced the missing cells and became functional for hearing instead (Sur & Leamey, 2001). In humans, when either visual or auditory loss occurs without damage to the brain, the area that would have been dedicated to providing sensory information is recruited for other Figure 5.6: Neuron growth and pruning According to scientists, the brain overproduces synapses during early childhood and then goes through a pruning process later. Neurons that receive the most stimulation are favored over those that receive less stimulation. Source: From Reynolds and Fletcher-Janzen, Eds, Handbook of Clinical Child Neuropsychology, Figure 4, p. 25. Copyright . 2009. Reprinted with kind permission from Springer Science+Business Media B.V. 144 © 2016 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution. mos82599_05_c05_135-180.indd 144 2/11/16 8:24 AM Section 5.1 Nervous System Development means (Merabet & Pascual-Leone, ...
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agneta
School: UIUC

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Running head: DAMAGE THEORIES

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Damage Theories
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DAMAGE THEORIES

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The human brain just like any other organ undergoes damage with time. The basic theory
of brain damage is based on the fact that any object that undergoes consistent use eventually
wears out. The brain is the central control unit of the body hence the gradual damage of the brain
is portrayed through physical a...

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