Principles Of Psychology

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( Unit 2 )

1. According to the Society for Neuroscience (2011), the field of neuroscience has grown from 500 members in 1969 to over 40,000 members (Cacioppo and Freberg, 2013, p. 131).

How could the field of psychology and neuroscience work congruently to benefit society?

Is neuroscience the “New Frontier” of the mind?

2. Cacioppo and Freberg (2013) stated, “Although we can identify structures that participate in certain behaviors, the biology of mind involves intricate and overlapping patterns of activity involving many richly connected structures” (p. 145).

Did this happen without the existence of God?

Does this alter your beliefs?

3. The case of Phineas Gage was discussed by Cacioppo and Freberg (2013, pgs. 158-159). How does learning about this case help you understand brain trauma?

Does this help you understand how behavior can change as the result of it? Why or why not?

4. Read Cacioppo and Freberg (2013, pgs. 160-161) “Psychology as a Hub Science: Law, Responsibility and the Brain”.

Does neuroscience have a place in the criminal justice system?

Before being paroled, would brain imaging help protect society? Why or why not?

( Must have a minimum of 1,000 words and three scholarly sources )

( Unit 3 )

1. How does life experience contribute to “perception” discussed in chapter five on pages 181-187?

2. Consider this statement “Helen Keller, who was both blind and deaf was asked which disability affected her the most, she replied that blindness separated her from things, while deafness separated her from people” (Cacioppo and Freberg, 2013, p. 209). As people age, hearing loss is a normal developmental change.

How does loss of hearing relate to loss of relationships?

What do you think?

Does this create a new sense of empathy in the aging process?

3. Ackerman (1990) stated, “Infants who are touched regularly sleep better, remain more alert while awake, and reach cognitive milestones at earlier ages (Cacioppo & Freberg, 2013, p. 219).

Why is touch important in the human experience?

Does this provide clarity on how nurture and nature interplay?

4. Zuscho (1983) stated, “People who have lost their sense of smell due to head injury often experience profound depression” (Cacioppo & Freberg, 2013, p. 223). This in opposition to Immanuel Kant’s position on smell.

Why do you think this occurs?

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Perceived social isolation or connectedness can produce changes in the cells of our immune system. M I L E S , S H A N N O N 1 9 0 9 T S 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. The Biological Mind TheMPhysical Basis of Behavior I L Learning Objectives E 1 Debate the strengths and limitations of biological psychology as a major psychological S perspective, considering the roles of monism, reductionism, and reciprocity between betwe biology , experience. and expe peri rien ence. 2 Anal Analyze lyzze the implications impliccations of of ad adva advances v ncces in n methods methods used d to to study studyy the th brain for o our ur unde ers rstanding of b iolo io logicaaS l psychology. psyycho holo ogyy. understanding biological 3 Explai Explain ain n what what it me mean means anss for a neuron on tto o “fi “fire” fire re”” an aaction ctio on pote potential, ent ntial, d describing escr es crib ibin ing ho how w th the neuron’s H A neurons communicate Explain Expla ain n the process by which commu mun nicate with each other, allowing the nervous system m to integrate inte tegr grat ate co comp mple lN x in info form rmat atio ion. complex information. Differentiate Differ rentiatee tthe he rroles oles ol es p played layyed la major ajor n neurotransmitters euro otranssmittteers iin n su sup supporting pporting physical ffunctioning Nd bbyy ma and psychological psyc ps ycho holo ogi gica call experience. exxpe peri rien encee. O of the nervous system, eexplaining Differentiate the major branches xpllain xp iniing the core biolo biological function of each branch. N structure makes this possible. © Argosy Publishing, blishing, g, Inc. 4 5 6 7 Associate key structures in, and regions of, the brain with important aspects of physical and psychological functioning. 1 by which hormones influence psychological experience and 8 Explain the process behavior, differentiating this process from neurotransmission. 9 0 Throughout history, human survival has 9 been threatened by the various bacteria and viruses that tryTto make us their home. The bacteria-driven Black S decimated Europe between 1346 and 1400, killDeath ing an estimated 30 to 60% of the population (Austin Alchon, 2003). Smallpox, measles, and influenza carried by Europeans to the Western Hemisphere killed as many as 90% of the native populations (PBS, 2005). The “Spanish flu” of 1918, which is related to contemporary bird flu strains, killed between 50 and 100 million people worldwide in a period of about one year (Patterson & Pyle, 1991). © A. Inden/Corbis 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 125 Courtesy of Dr. Skirmantas Janusonis/University of California, Santa Barbara. Photo © Roger Freberg Human brains like this one, carefully held byy one of your authors,, weigh about con onta t in three poundss and contain approximatelyy 10 100 billion 00 bi b llio on t’s about th he same neurons. That’s the number as thee stars st s in our galaxy, y, y y. the Milky Way. 126 We have not been passive bystanders to this devastation. Even though pandemics like the Black Death have caused remarkable destruction, none has killed the entire human population. The survivors often possess some natural, protective resistance to infection, which might then be passed along to their descendants. In some cases, resistance to one type of organism offers protection from completely new organisms. Researchers studying the HIV virus, which causes AIDS, discovered that some people seemed unusually resistant to the virus due to a particular genetic mutation. The mutation is common among northern Europeans, relatively rare in southern Europeans, and completely absent among Asians, Africans, and Native Americans. Some researchers believed surM viving the bacterial infection of the Black I Death was related to the frequency of the L mutation, while others point to surviving smallpox instead (Galvani & Slatkin, 2003). The discussion so farE might sound more like biology or medicine than psychology, but behaviorSand mental processes have a considerable amount of influence on our abilities B , to fight bacteria and viruses (Cacioppo & Ber2011). Once human social environment ntson, 2 011) 01 1). On nce aagain, gain n, zo zzooming om min ing ou outt to tthe h hum he uman soc cia iall en envi v ro onm nmen en again much scale complete and zooming zo ooming back baackk iin n aga ain n to a m uch uc h smaller sc cal ale gi ggives vees us a com mpllet etee and S interesting intere est stin i g picture. pictu uree. Human beings, who impressive teeth claws, formed Hu uma man n be b in ngs gs,, wh w oH lack imp la mpresssiv ivee te teet eth h or cla law ws, fo form rmed ed ggroups roup ro up to enhance the odds of their survival. Anyone who was socially excluded exclud A these groups experienced hostile environment. from the hese group ps expe p rienced a moree h ostile environme ent. Social excluex separated sion not ot onlyy se sepa paraate ted d aNperson pers pe rson on from fro rom m the th help heelp of of others othe ot hers rs in in life-threatening life-threate situations, but worse, situatio ons, perhaps perh pe rhap ps in fending fen n off a predator, prredaator or, bu ut wo wors rsee, could lead to Ndinng off ciroutright ht conflict con onfli flict ct with wit ith h others, othe ot herrs, including in nclud din ingg combat. com mbat at. Under Unde Un derr such hostile ci O cumstances, socially excluded people faced a greater bactecumstances great ater e risk ris isk from bacte rial infections than fromNviruses. Bacteria enter the body through cuts and scratches, whereas viruses are transmitted through body fluids (e.g., sneezing), so you are most likely to be exposed to them when you are in 1 close contact with other people. 9 in mind, take a look at the group of people in the With that background image on the preceding page. 0 Do you think the woman on the left is feeling included or excluded? Surprisingly, whether we typically feel socially 9 isolated or socially connected can have serious implications for our health (Cole, Hawkley, Arevalo,T& Cacioppo, 2011). If this woman normally feels isolated and often left toS fend for herself, she will, like her excluded ancestors, face a greater threat from bacteria than from viruses. In that case, her brain will generate hormonal signals that will tell her immune system (shown in the larger image) to gear up to protect her against bacteria. In contrast, if she usually feels socially connected to others, her brain will initiate a cascade of hormonal signals that tell her immune cells to prepare to protect her against viruses. This is just one example of how the mind’s perceptions of the social environment—whether it is friendly or not, for instance—can impact biological processes that are important to health and survival. Chapter 4 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. In the previous chapter on nature and nurture, we learned how the challenges of surviving and reproducing in particular physical and social environments could shape a species’ biology and behavior. In turn, the resulting biological structures and processes of the mind exert profound influences on our physical and social environments. In this chapter, we will provide a foundation for understanding the biological bases of behavior and mental processes by exploring the structures of the nervous system and the ways that they function. E What Is Biological Psychology? © Dimi Dimitri D imitri tri Iundt/TempSport/Corbis Iundt Iu Many of us find the concept that our “minds” are somehow a result of the activity of nerve cells a bit unsetM tling. How could our feelings, thoughts, and memories I be caused by a bunch of cells? Shouldn’t there be more to who I am than something so physical? Such ideas L led thinkers like René Descartes to propose a philosophy of dualism, which suggests that “mind” is somehowEdifSare ferent and separate from our physical being. If you moree comfortab comfortable with ble w ith thinking about mind this,way, go right recognize that ght ahead, as long lon ong as you rec ecog ogni nize tha hatt thee fie field of biological ologi gical psychology, psyccholo ogy, and the th he neurosciences neurosciien nce ces in n gengen enS eral, embraces the competing philosophy monism. h com ompe peting p hilosophyy off mon nism. m. According monistic what rdiingg to the m rd onisticc approach, approa oach ch,, th the mi mind nd is H what the brain raiin does. A Biological interdisciplinary Biolog gicaal psychology psych chol ologyy is a rich, ri interdiscipl p inaryy field of study stu st udyy that combines methods theories psychology those off bi biology, bines thee m etho et h ds and theo oriies of p sych sy chol olog ogyyNwi with th tho hose se o biol log ogy,, physiology, the neurosciences, related iology, biochemistry, bi neu uro oscien ences, and and other otN her er relat ated fields. fieldss. While fi W ilee Wh investigating behavior, tigating a particular behavio or, the the biological bio iolo logi gica call psychologist psyc ps logist st focuses foc ocusses on on Oycholo links between observed behavior and genetic factors, factors biochemical factors, factors and the activity level and structural characteristicsNof the nervous system. These links do not travel in one direction only, from biological factors to behavior, but are more accurately viewed as reciprocal. For example, we 1 know that if you administer extra testosterone to human males, raising their testosterone to above normal levels, they are9 likely to behave more aggressively (Pope, Kouri, & Hudson, 2000). In this 0 case, biology (raising testosterone levels) is influencing behavior (aggression). However, we also 9 know that watching his favorite sports team lose lowers a man’s testosterone levels (Bernhardt, Dabbs, Fielden, & Lutter, T 1998). Here we see the influence of behavior (supporting a particular teamSand watching the team lose) on biology (testosterone levels). Advances in the methods we use to observe the structure and function of the nervous system have driven the history of biological psychology. The discovery of contemporary methods, such as the recording and imaging of brain activity, opened whole new areas of inquiry to biological psychologists. Before these methods were available, however, most of our knowledge of the nervous system Early Attempts to Understand Biological Psychology Not only does biology infl influence (thinking about behavior, but behavior (th winning winn wi nnin ing g aand n losing in this case) affects nd biology. biol bi olog ogy. Players and even the fans of a winning winn wi nnin i g team experience a temporary increase while the incre in easse in testosterone, w players and l d ffans off the h llosing team experience a temporary decrease in testosterone. biological psychology The interdisciplinary field of study that combines the methods and theories of psychology with those of biology, physiology, biochemistry, the neurosciences, and other related fields. WHAT IS BIOLOGICAL PSYCHOLOGY? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 127 resulted from clinical observations of injured or mentally ill individuals or autopsy, the examination of bodies after death. When used together with contemporary methods, clinical observation and autopsy are quite accurate, but early thinkers lacking contemporary methods often struggled in their attempts to understand the physical basis of mind. They understood many things correctly while making some notable errors. Aristotle, who was accurate on many issues, mistakenly believed that the heart, not the brain, was the source of mental activity. An interesting historical mistake was phrenology. Toward the end of the 18th century, phrenologists proposed that the pattern of bumps on an individual’s skull correlated with his or her personality traits and abilities Autopsy has been used since 3000 BCE, and it remains a useful source of information, especially in forensics. Dr. Bill Bass, a forensic anthropologist, studies donated bodies as they decompose at the “Body Farm” at the University of Tennessee, Knoxville. The knowledge gained from these investigations makes it possible to determine time of death at crime scenes. Photo © Jon Jefferson; courtesy of M I L E S , Thinking Scientifically S H A When Doe Does es Re Reductionism eductionism m Wo Work? ork? N When Does Doe es It It Fail? Fail? N O signaling, is participating in neural eductionism ductionism in science is flavoring our food, contributing to defined as the explanation N R of complex things as sums of simpler things. Taking a rather extreme reductionist approach, science fiction often features scenes in which an android reminds a human that they’re really not so different after all—the brain is just a computer made up of chemicals, nothing more, nothing less. In some ways, all modern science is reductionist. Scientists assume that whether you are studying particle physics or human behavior, a single set of fundamental laws explains much of what we observe. We do not need new sets of rules for the features of table salt (sodium chloride) in each context in which it appears. Regardless of whether the chemical 128 Chapter 4 | high blood pressure, or making us float more easily when we swim in the ocean, the fundamental 1 principle is the same: salt is salt. 9 for fundaThe scientific search mental principles has 0 been fruitful, to say the least, but it does have limitations. Although 9 we can learn a lot by breaking apart complex things T to study simple things, we saw some S in the of the risks to this approach debates between the structuralists and Gestalt psychologists. Fish swim in schools, geese and ducks fly in a V-formation, ants and bees swarm, cattle form herds, and human beings form societies. We could never understand these more complex phenomena by studying the behav- ior of an in indi d vi di v dual member of th individual the group. Nobel laureate physicist P. W. Anderson reminded scientists that large collections of simple things do not always behave the same way that simple things behave in isolation. He wrote that “at each stage (of complexity) entirely new laws, concepts, and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology, nor is biology applied chemistry” (Anderson, 1972, p. 393). This chapter on the biological foundations of behavior and mental processes relies extensively on reductionist thinking. As you work through the chapter, however, it is important to keep Anderson’s cautions in mind. We will begin by analyzing the mind THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Phrenologists believed that “reading” the bumps on a person’s head, using a bust like this as a reference, could tell them about a person’s character. rsto S H A N N O N © Terry Why/Phototake Viewing a complex conce Viewing View concept as a sum of its ts ssimpler impler parts is not always the its full h best b way to understand d meaning. utte ©F abi oF ersa /Sh at the cellular level by examining nerve cells and their activity. Then our view zooms out from cells to the larger structures of the brain and spinal cord to circuits to systems to beyond the body itself with social interactions among other systems (i.e., other people). As we embark on this journey, it’s important for you to remember that some aspects of behavior will continue to be governed by rules that explain the actions of simple things, while others will require the introduction of new rules better suited to more complex combinations and interactions of simple things. E ck (Simpson, 2005). The brain supposedly worked like a muscle, getting larger through use, leading frequently used areas of the brain to grow so much that the skull above these areas would bulge. Phrenologists “read” a person’s character by locating the bumps on a person’s head and identifying the personality traits below each bump according to a map. None of these ideas, of course, was close to being accurate. Phrenology was especially popular in the United M States during the latter half of the 19th century, with employers asking prospective I employees to undergo phrenological exams, young lovers seeking exams L to ensure compatibility, and even presidential candidates submitting to exams (Stern, 1971). Although the phrenologists were wrong about the E significance of bumps on the skull and the effects of activity on the strucS ture of the brain, they did reach one correct conclusion. Their notion that somee behaviorall func functions localized off the br brain ctions are locali lize zed to o ccertain erta er tain ,aareas r as o re rai ain n is onee we share haree ttoday. oday od a. 1 9 0 9 T S © nito/Shutterstock WHAT IS BIOLOGICAL PSYCHOLOGY? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 129 More modern perspectives of the nervous system emerged from the work of scientists like 19th-century neurologist John Hughlings Jackson (1835–1911). Based on observations of his patients with seizure disorders, Jackson proposed that the nervous system is organized as a hierarchy, with progressively more complicated behaviors being managed by more recently evolved and complex structures (Jackson, 1884). We can see Jackson’s hierarchy at work when we observe people drinking alcohol. Alcohol specifically decreases the activity of parts of the brain involved with judgment and decision making. When a person has had too much to drink, the more complex social controls (such as knowing how close you should stand to a stranger) normally provided by higher level areas of the brain are diminished. Without the influence of these controls, M people start doing things that they would not typically do while sober. This I the now unrestrained influence of the more change in behavior reflects primitive parts of the brain L involved with behaviors such as aggression and sexuality. You might, for example, pick a fight with someone when you E normally think fighting is wrong. The aggression and sexuality were there S activity of the higher levels of the nervous sysall along, but the normal circumstances tem usually restricted their , expression to more appropriate circumsta 2008). (Siever, r, 2 008) 00 8). Contemporary Approaches in Biological Psychology TABLE 4.1 Research method d Skin conductance ctance respo response ponse e (S (SCR; formerly known galvanic own ass ga galv lvanic skin response) Electroencephalogram phalogram (EEG) What questions can we answer? What W at iss a person’s Wh persson pe on’s ’s state sta tate te of of arousal? What is a person’s persson n’s state sta tate of arousal? Evoked potential Measurement formed by averaging EEG responses to a stimulus, such as a light or tone Did the person perceive the stimulus? Single cell recording 1 9 Recording of the tiny amounts of0magnetic output of the brain 9 Uses the accumulation of radioactively tagged T glucose or oxygen to identify activity levels in parts of the brain S What types of stimulation make this neuron respond? Functional magnetic resonance imaging (fMRI) Identification of active parts of the brain using magnetism to track the flow of oxygen What parts of the brain are active during a particular task? Electrical stimulation Application of small amounts of electricity through a surgically implanted electrode What behaviors occur if we stimulate this part of the brain? Transcranial magnetic stimulation Application of magnetic fields to the brain through an instrument held near the scalp What behavioral changes occur when magnetism is applied to the brain? Lesions Naturally occurring or deliberate damage to the What behavioral changes are correlated brain with brain damage? Magnetoencephalography (MEG) Positron emission tomography (PET) 130 S H Description A Measurement Measurem ment of electricity elect ectri rici c ty passed pas asse eN d between betw be twee een two two surface electrodes elec ectrode es placed pla lace ced d on the the skin skkin n of the he N hand or finger finge fi g r O activity Measurement of the brain’s electrical using electrodes placed on the scalp N Research Rese sear se arch Methods iin ar n Biolo Biological ogical Psy Psychology sych sy chol ch olog ol ogy og Chapter 4 | Measurement of a single neuron’s activity obtained through a surgically implanted electrode What parts of the brain react to this stimulus? What parts of the brain are active during a particular task? THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. The 20th century saw a burst of knowledge about the nervous system, culminating in the 1990s being designated by the U.S. Congress as the Decade of the Brain. Our understanding of the correlations between brain and behavior leaped forward with continuing improvements in research methods, including many of those found in Table 4.1. In particular, methods that allow scientists to observe the activity of the living brain, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), began to answer questions that were impossible to study previously. Because of these improved methods, today we can talk about how the brain responds differently to images of faces and places (Downing, Chan, Peelen, Dodds, & Kanwisher, 2006), “feels” the pain of social exclusion (Eisenberger, Lieberman, & Williams, 2003; Eisenberger, 2011), and develops abnormally in teens diagnosed with schizophrenia (Thompson et al., 2001), which we discuss in a later chapter on psychological disorders. MovM continue to grow, ing into the 21st century, the ranks of neuroscientists I in 1969 to more than from 500 members of the Society for Neuroscience 40,000 members today (Society for Neuroscience, 2011). L E S , zooming in to see its We begin our exploration of the nervous system by microscopic osco opi picc building b il bu ildingg blocks, the he nerve nerve cells, ceells ls, or neurons. neur ne uron ns. Human Hum Hu man brains brains ns have about 100 billion neurons. To this ut 1 00 b illi il lio on n e ronss. T eu o put thi hiss number numb bSer in n perspective, persspecttiv pe ive, e, concon onsider the off the following. g If If a neuron n uron ne on represented rep epre r seent nted ed a second, seecon nd, d ticking ticcki king ng o ff th the neurons o s in your body on dy alone alo lone would d take take k more thanH3,170 years! With With h each A neuron forming with on for rmi m ng aan n average of sseveral everal thousand connections ev wit other neurons, in the hundreds ons, the the cconnections on nnectio ons in the human hu uman n brain brai br a n number numb nu mber er i n th e h hu ndreeds of nd of N trillions. addition neurons, nervous ons. In n ad addi d tion tto o these largee numbers numb mber erss of n eurrons eu ns, thee nerv rvou us system sysstem m also contains many supporting ce cells, glia. ellls, kknown nown no wn aass gl glia ia.N O and glia, we will turn Once we are familiar with the structure of neurons our attention to the way neurons communicate with N one another. Neural communication is a two-step process. The first step takes place within a single neuron and involves the generation of an electrical signal. The second 1 release of a chemical step takes place between two neurons and involves the messenger from one neuron that impacts the activity 9 of the second. 0 Neurons share many characteristics with other cells found in the body. Like other cells, a neuron has a 9 large central mass, or cell body, and within the cell T body, a nucleus (see ● Figure 4.1). Most of the typical housekeeping tasks of the cell, such as the translation of genetic codes S into the manufacture of proteins, take place in the cell body. Like other cells, neurons feature an outer membrane, which surrounds the neuron and forms a barrier between the fluid outside the cell—the extracellular fluid—and inside the cell—the intracellular fluid. The neural membrane is composed of fatty materials that do not dissolve in water, so even though it is only two molecules thick, it is able to hold the water-based fluids on either side apart. Pores within the membrane act as channels that allow chemicals to move into or out of the cell across the membrane. Neurons and Glia © Peter Fromherz/Max omher mherz/M z/Max ax Pla Planck Institute off B Biochemistry ioc ochem hemist is ry How Do Neurons Communicate? This neuron has been grown on a silicon chip, a line of research that might lead to better treatment for people with amputated limbs. Prosthetic devices, like an artificial leg or hand, could possibly communicate directly with the person’s nervous system. neuron A cell of the nervous system that is specialized for sending and receiving neural messages. cell body The large, central mass of a neuron, containing the nucleus. HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 131 Axon terminals (a) Parts of the neuron Cell body Nucleus Axon Dendrites Positive ion _ + Neurotransmitters + _ Pore Intracellular fluid _ + _ _ Close se-up -up of of the (b)) Close-up axon membrane _ M I L E S , Dendrite Receptors Syn Syna aptic vvesicle esic icle Synaptic (c) Cl lose-up -up vi view e Close-up © Argo Argosy Arg syy Pu Publishing, ub blli Inc. Extracellular fluid Axon terminal S o th of he ax a on te erm mina al the axon terminal Synaptic Sy cg ap gap H Figure 4.1 A The Neuron.. Neurons Neurrons share sharee many ffeatures eatures with o ea other th her livin living ng ce cells, but but are are spe specialized peci cial aliz i ed for for tthe he processing pro roceess ssin ing g of o information. inffor orma mati tion on.. (a) Parts of th on the typess of ani nima m l ccells, ells, the neuro on features featu ures es a nu ucleus us iin nN its ce ell bo odyy and a ffatty attty me emb mbraanee tthat hatt se epa parates the intrace Neuron. Likee other types animal neuron nucleus cell body membrane separates intracellular and extracellular branches, ular fluids. Unlike most other cells, thee neuron neuron n has has specialized spe pecciaalized edN brran nchess, the the axon axxon n and dendrites, deendrittes,, that tha hatt pass pass information to aand mation from other cells. (b) A Close-Up Up View Vie iew w of tthe he Axo xon n Me Memb brane. A thin n oily oilyy membrane mem mbran ne separates seepa para rate tess the intracellular flu receive information Axon Membrane. fluid Othe membrane that act as channe inside the neuron channels, uron from the extracellular fluid outside the neuron. Pores span neels, wh which allow ions to move m in or out of the neuron. (c) A Close-Up View of the Axon Terminal. Within the axon terminal are synaptic vesicles, which contain chemical N Negative ve io on ion messengers called neurotransmitters that transmit signals between neurons. Later in the chapter, we’ll see how these neurotransmitters communicate with receptors on the dendrites of other neurons. 1 axon The branch of a neuron that is usually responsible for transmitting information to other neurons. dendrite A branch from the neural cell body that usually receives input from other neurons. 132 Chapter 4 | Unlike many other types of body cells, neurons have two types of 9 the cell body to allow the neuron to perform its branches that extend from information-processing and 0 communication functions. The branches known as axons are responsible for carrying information to other neurons, while the 9 branches known as dendrites receive input from other neurons. Although neurons may have many T dendrites, they typically have only one axon. Many axons communicate with immediately adjacent cells and are S therefore only small fractions of a millimeter in length, but other axons are quite a bit longer. When you stub your big toe on a rock, the neurons that process this information have cell bodies in your lower back and axons that extend all the way down to your sore toe, a distance of around three feet, depending on your height. At its farthest point from the cell body, an axon bulges to form a terminal. If you look inside an axon terminal with an electron microscope, you can see round, hollow spheres, known as synaptic vesicles, which contain molecules of chemical messengers. THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Reprinted with permission from the American Journal of Roentgenology © Argosy Publishing, Inc. You have probably heard the terms gray matter and white matBlood vessel ter used to describe the brain, Neuron but you might not have understood exactly what these terms mean. Now that you understand the structure Glia of neurons, the terms will make more sense. Live neural tissue looks rather pink. When we prepare neural tissue for study using microscopes, the chemicals used to preserve M the tissue are absorbed by I cell bodies, giving them a pinkgray coloring. In contrast, these L chemicals are repelled by the insuE lating material covering most axons S because the insulation has a fatty compoFigure 4.2 sition n that doesn’t doesn n t mix mix well with the watery pre- , The e Blo Blood-Brain lood-Bra ain n Barrier. r. G Glia lia ia form form ttight ig ght co connections o servatives discuss atives (we d iscusss the naturee of this thi his insulation in nsu sula lation n shortly). shorttly ly). Th bloo od vessels ves essels iin n tthe he nervous system, syystem preventing As a result, wee with the blood resu ult, axons axxonss lookk white, like likke tthe he fat in n a ssteak. t ak.. Wh te When nw any to oxinss fr from om eentering nter erin ng th he br b ain. Gli liaa al als many toxins the brain. Glia also help hold S a hhigh examine brain, areas mine images off thee b rai ain, are eass that look ok gray ha have iggh ma neurons myelin some axons. neuro ne onss in n place pla lace and and d form forrm th tthee m yeelin n on som density bodies, whereas areas white consist ityy of cell bodie it es, wh hereas ar rea eass th that llook ook oo k wh hH ite cons it nsist of large rge ge bundles bundles of axons. axon ons. A Frontal lobes Iff neu neurons nervous uronss aree the he sstars t rs of the ne ta ervous system syystem team, Ny glia are the th he trainers, trrain ner ers,, coaches, coaches, and an nd scorekeepers. scor orek ekee eepe pers rs. They The makee it possib possible ible for the neurons to o do o ttheir heiir jjob he ob eeffecffecff Nctively. y. Some glia (from the Greek word word for for “glue”) “gl glu ue”) ”) provide pro rovvide Ode a structural neurons, ensuring that the neu neuuctural matrix for neurons N rons stay in place (● Figure 4.2). Other glia are mobile, allowing them to move to a location where neurons have been damaged to clean up any debris. Glia form tight 1 connections with the blood vessels serving the nervous 9 system. This forms a blood-brain barrier that prevents many toxins circulating in the blood from exiting into 0 brain tissue where neurons could be harmed. Psychoac9 tive drugs, by definition, are substances capable of penT etrating the blood-brain barrier with ease. We discuss psychoactive drugs and the ways in which they actSon The image on the left shows myelin (in white) in the brain of a 2-year-old child. The image on the right shows the much greater the nervous system in our chapter on consciousness. amount of myelin in the brain of an 18-year-old. Myelination of In vertebrates like us, glia wrap around some axons the human brain is not complete until a person is in his or her like sausages on strings at a delicatessen, forming an early to mid-20s. The last areas to be completely myelinated are important layer of insulation called myelin. Myelin the frontal lobes, which are involved in self-regulation, decision makes neural signaling fast and energy efficient. We making, and judgment. will discuss how myelin accomplishes this in a later section on neural signaling. Not all axons in the human nervous system myelin The insulating material covering some axons. are myelinated. When you hurt yourself, that fast, sharp “ouch” message is 133 carried to the brain by myelinated axons, but the dull, achy message that lasts a lot longer is carried by unmyelinated axons. One type of glia forms the myelin in the brain and spinal cord and a second type forms the myelin in the remainder of the nervous system (see ● Figure 4.3). These two types of glia behave quite differently from each other when they are damaged. Glia in the brain and spinal cord form scar tissue, inhibiting repair to the damaged nerves. Because of this The blood-brain barrier might offer too feature, we consider damage in these parts of the nervous system to be permanent. Obviously, considerable research is under much protection to the brain in some way to figure out how to repair such damage, including work cases. Many chemotherapy agents used to treat cancer in other parts of the body using stem cells to grow bridges across the damaged areas. In contrast, damaged glia in areas of the nervous system outside cannot penetrate the blood-brain barrier, the brain and spinal cord do not form scar tissue and actually which complicates the treatment of help the damaged axons regrow. As a result, nerve damage in M heal. If this were not so, operations to reattach tumors in the brain. these areas can limbs would be doomedIto failure. Nowadays, not only are digits and even limbs that were lost inLaccidents routinely reattached to their rightful owners but a number of patients whose own hands or faces were damaged beyond repair haveEundergone successful transplants from cadavers Figure 4.3 S (Clarke & Butler, 2009; Dubernard, Owen, Lanzetta, & Hakim, 2001). As we explore further, in our chapter on development, myelin grow growth in Glia Form m Myelin. One type the human nervous system begins before birth, but it is not completed huma man n nerv ne v ou u s sy em beg g ins in be e fore fo re b irth, bu no t com co m ple lete ted d until of glia forms myelin the ms my myel elin in in th he early adulthood, possibly late the last of adulthood ad d , p ossibl os l y as lat t e as s t he age g of 25. 25 The la a st area o f the th e nerbrain and spinal spin nal cord, d, and da S vous system located right sys ystem to be be myelinated myelin inated ed iiss the th he part partt of of the th he brain brai br ain lo locate t d righ ghtt behind be second type pe forms myelin in the restt of the hee nervous your your eyes, eye yes, which yes, which ch iiss involved inv invo vH volved olved with with judgment judg ju udg dgme dgm men m ent nt and nt d morality moral orralit alityy (Hayak (Hay ((H Hayyakk eet al., system. These hesee ttypes ypes of glia respond differently ifferent ntly ly to to nerve nervve damage, making g nerve ve damage outside brain utsidee tthe he b rain and nd spinal cord easier d easi ier to repair. (a) Glia in the brain and spinal cord A N N O N Glia 1 9 0 9 T S Axon © Argosy Publishing, Inc. Glia 134 Chapter 4 | Myelin Axon Ax Myelin Axon Axon Myelin (b) Glia outside the brain and spinal cord THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Alba Lucia Cardona of Colombia lost both hands in an accident 30 years ago and recently had two cadaver arms surgically attached. This type of operation would be useless unless the nerves in her arms could communicate with her new hands. a/ va no © Ing ck sto tter u Sh Iva Courtesy of USGS, Alaska Science Center. Photo by Mayumi Arimitsu. Now that we have a working knowledge of the structure of neurons, we are ready to talk about how they function. A neuron is a sophisticated M that receives input, communication and information-processing system evaluates it, and decides whether to transmit any Iinformation to neurons downstream. Its actions are similar to your own when L you receive a juicy bit of gossip from a friend, and then decide whether or not to tell somebody else. E is a two-step process. As we mentioned earlier, neural communication In the first step, which takes place in the signaling S neuron’s axon, the neuron generates on generat tes e an n electrical signal known as an, action potential. This signal travels traveels thee length of the he axon axo on from frrom its its t junction jun unct c ion n with w th wi h the cell body bod dy to o its terminal. terminal. In n the the second seco ond d step, step,, which whi hich h takess place between betw ween two two neurons, neurron ns, the arrival arrriival of oSf an action potential n pot oten e tial at the th axon on terminal termi mina nall of thee first firs fi rstt neuron neeH uron signals alss the al th release off chemical che hemical messengers, which float A across separating ss thee extracellular ext x raccell llul ular a fluid sepa arating the two neurons. These Thesse chemicals che h mi micalss influence the th he likelihood like li keli liho hood od tthat hN att the second with econd d neuron will respond w ith it itss own n action acti ac t oN n potential, along. ntial, sending the message alo long ng. Neural Signaling © Kai Forsterling/epa/Corbis 2001). Until myelin in this area is mature, these neurons do not work as efficiently, which is one of the possible reasons why teenagers sometimes make different decisions than adults (Baird et al., 1999). You may recall some experiences from your early teens that appear shocking and overly risky to your adult brain. Worse yet, as you move through your 20s, you might find yourself agreeing more frequently with your parents. O Electrical Signaling The production of action potentials can be demonN strated using axons dissected from a squid and placed in a tub of seawater, which has a chemical composition similar to the fluid surrounding our body 1 cells (Hodgkin & Huxley, 1952). Of all the possible sources of axons on earth, why choose squid? Axons from a squid can be as much 9 as 1 mm in diameter, large enough to see with the naked eye. The squid axon 0 is also large enough that you can insert a recording electrode into its interior without disrupting its function. The readings from inside the axon can9then be compared with T readings from a recording electrode placed in the seawater. When a neuron is not processing information,S we say that it is at rest. When a cell is at rest, the difference between the readings from the interior of the axon and the external fluid is known as the resting potential. Our recording will show that the interior of the neuron is negatively charged relative to its exterior. Let’s assume that our resting neuron now begins to receive chemical messages from another neuron, a process we discuss in more detail shortly. Neurons can respond to incoming chemical signals by becoming either depolarized or hyperpolarized. The word polarized means “far apart,” as when political factions disagree. Being depolarized means we have moved Squid axons are large enough to be seen with the naked eye and will remain active in a bath of seawater for hours. These features make studying neural activity in the squid axon relatively simple. action potential The electrical signal arising in a neuron’s axon. resting potential The measure of the electrical charge across a neural membrane when the neuron is not processing information. HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 135 Resting Action potential Refractory period Resting 3 40 mV 2 0 © Cengage Learning 2013 Potassium channels open; potassium starts to leave cell. 3 Sodium channels close. 4 Potassium channels close. The Action Potential. Once threshold is reached, an action potential is triggered. The movement of sodium and potassium ions across the axon membrane is reflected in the rise and fall of our recording. A refractory period follows each action potential, during which time triggering another action potential is mo ore difficu cult lt. more difficult. M I L 4 E S , Depolarization –65 –70 Hyperpolariza ation Hyperpolarization 0 1 2 Time e (in (in m sec) msec) 3 S Depolarizin Dep ng Depolarizing input ut H A closer to together ogethe her an and d be bein being ing hype hyperpolarized perp rpol olar arizzed e means mea ean ns we we have have ve moved even farN hy apart than before. the neurons, depolarization ther apa part tha han n be befo fore re.. IIn n th he ccase ase of n euro eu onss, de epo pola larrization means that difference between the electrical off th the diffe ffere renc ncee be betw twee een nN th elec ctriccal charges charg rges o thee ex extracellular and the is decreasing. Hyperpolarization intracellular recordings O Hyperpolar ariz izat atiion means that tha the difference is increasing. N I like nonsense; it the brain cells. —Dr. Seuss 136 2 Figure 4.4 1 Threshold Resting potential 1 Sodium channels open; sodium rushes in. Chapter 4 | When a neuron is depolarized by sufficient input, it will reach a threshold for producing an action potential. A threshold is the point at which an effect, 1 case, is initiated. Once this threshold is reached, the action potential in this the generation of an action 9 potential is inevitable. Approaching the threshold of a neuron is similar to pulling the trigger of a gun. As you squeeze the trig0 you reach a critical point. Once that critical point ger, nothing happens until is reached, the gun fires, 9and there is nothing you can do to stop it. Reaching threshold initiates a sequence of events that reliably produces T an action potential (● Figure 4.4). These events involve the opening and S in the neural membrane, which in turn allows closing of pores, or channels, certain chemicals to move into or out of the cell. These chemicals wakes up are in the form of ions, or electrically charged particles dissolved in water. When threshold is reached, channels open allowing sodium ions to rush into the neuron. Because sodium ions carry a positive electrical charge, we can see their movement reflected in a steep rise in our recording of the difference between the internal and external electrodes. At the peak of the action potential, our recording has THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Image provided by Professor Manzoor A. Bhat at the University of North Carolina School of Medicine, Chapel Hill, NC © Joe Scherschel/National Geographic Stock completely reversed itself from the resting state. Now the interior of the cell is more positively charged than the outside. Near the peak of the action potential, channels that allow positively charged potassium ions to move across the membrane begin to open, and potassium begins to leave the cell. As the interior loses these positively charged potassium ions, our recording heads in the negative direction again. Following the production of the action potential, the neuron requires a time-out, or refractory period, during which it returns to its resting state. During this refractory period, the cell is unable or unlikely to respond to further input by producing another action potential. The size and shape of action potentials are always the same, whether we’re recording them in a squid or in a human. M You won’t see any recordings of short, fat action potentials or tall, skinny ones. Either an action potential occurs,I or the cell remains at rest—there is no middle ground. Because L of this consistency, we say that action potentials are all-or-none. Action potentials do not affect the entire axon E all at once. S in a very The process we have just described takes place first smalll segment o off thee axon where the axon connects, to the cell body.. The next sstep tep iiss propagation, propagatio on, or or the t e duplication th dupl du plic i attio ion n of the h electrical ele lect ctri rica cal siggnal down length off the axon axon terminal, initiate own n thee len ngth o n to the axo on te term r in nal al, wh where it will initia ate S the release messengers. elease off chemicall me messenge gerrs. We mentioned men e tioned earlier earlierr that myelinated myel my elin inaated d neurons neu eurons ns enjoy oyeed some som omee advanadva ad van nH enjoyed tages in efficiency and d speed, speed, and we are now ready to discuss whyy that is A the case. ase. Propagation Prop Pr pagaatio ion n takes t kes placee differently ta differently in myelinated and unmyelinunmye y linNntia ated axons axons. unmyelinated potentials ns. In n aan n unm myelinated aaxon, xon, n, aaction ctio ct ion n po pote ten ialls occur occ ccur ur in in a stepstep st ep-by-step to the next, adjacent ep manner, from one small section seection on off the the axon axon t o th h e n ex x t, , adja ad jacent nt N section, contrast, potentials on, down the entire length of tthe he aaxon. xon xo n. IIn n co con ntra action on p oten ential alss Orast, ac in myelinated yelinated axons are formed only at the sections of the axon membrane N of Ranvier. In other between adjacent segments of myelin, known as nodes words, propagation in myelinated axons can “skip” the sections covered 1 9 0 9 T S Sushi made made from fro rom puffer pu uffe fferr fish, fi known as fugu,, iss a delicacy, but bu ut prepared pre poorly Chefs ccan ca n result r sult in re in sickness sick ic neesss or or death. d w ho prepare prep pr epare fugu fuggu undergo und dergo extensive who training tra tr aining g aand nd llicensing icensiing iin ic n JJapan. The puffer fish toxin blocks the th movement making electrical of sodium into cells, maki sign si gnal alin in ng impossible. impossible. As a result, signaling diners fugu dine di ners rs who eat poorly prepared pre can ca n become b come paralyzed and suffocate be t death. to deatth. Nodes of Ranvier (stained blue) are rich in sodium channels (stained green), which makes the formation of action potentials at the nodes possible. In contrast, there are no channels in the membrane covered by myelin (shown in red). HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 137 by myelin. You might think about the difference between propagation in unmyelinated and myelinated axons as being similar to shuffling your feet versus taking long strides. Which covers the most ground faster and more efficiently? Propagation in unmyelinated axons works well, as evidenced by the wealth of invertebrate life on Earth, from the snails in your garden to the giant squid of the oceans. These animals survive with no myelin at all, but their neural communication is not very fast or energy efficient compared to ours. Forming action potentials at each section down the length of the axon is time-consuming, like taking the local bus that stops at every block. In addition, cleaning up after all these action potentials uses a lot of energy (Swaminathan, Burrows, & McMurray, 1982). The more action potentials it takes to move a signal down the length of the axon, the more energy is expended returning the cell to its resting state. M Propagation in myelinated axons is fast and efficient (● Figure 4.5). I After an initial action potential is generated near the cell body, the current flows beneath a segmentLof myelin until it reaches a node of Ranvier, where another action potential occurs. Like the express bus, the action potentials E of the axon, reaching their destination, the skip the myelinated sections axon terminal, about 20Stimes faster than if the axon were unmyelinated. myelinated By covering the same distance with fewer action potentials, the myelin , uses returning potential unmyelinaxon u sess less se lesss energy le eneerg rgyy re etu turn r ingg to tthe he rresting esti es t ng p otentiall tthan ot han ha n aan nu nmyy nm need. ated aaxon xon would xo d ne need e . Once action potential axon neural Onc On ce the ac ctio ion pot tS en ntia iall reaches reacche re hes th thee ax xon tterminal, ermi er mina nal, tthe he neur rall ccommunication from electrical signaling system to a chemim unicaati tion on system syste tem m switches switch sw ches fro rom m an n e lect le ctr r ica cal l sign n aling al g syst sy stem em o ch H cal signaling one. Myelinated axon Propagation of the Action Potential. Action potentials move down the length of the myelinated axon more quickly than in an unmyelinated axon. ++ _ Cell body 1 9 Node of Ranvier 0 9 T S Unmyelinated axon + + _ _ _ _ _ _ ++ _ _ + Myelin + + Current flows under myelin + _ _+ _+ + _ _ _ _ _ + + + _ + ++ + ++++ ++ _ _ _ _ + _ _ + + _ + _ __ _ _ _ _ _ _ _ + + + Action potential 138 Chapter 4 | + © Argosy Publishing, Inc. Figure 4.5 A N N Action Action potential potenttial O _ _ N+ +_ ++ THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. left: © Omikron/Photo Researchers, Inc.; right: © Dennis Kunkel Microscopy, Inc./Phototake Axon terminal of neuron sending information Synaptic vesicles Synaptic gap (a) (b) Dendrite of neuron receiving information (a) Axon terminals from many neurons are forming points of communication, known as synapses, on a cell body. (b) We zoom in for an even closer look at the features of a single synapse. M I ABLE T L 4.2 Important Neurotransmitters Chemical Signaling The point of communication E Behaviors influenced between two neurons is known as a synapse. At S Neurotransmitter by the neurotransmitter the synapse, neurons neeuron ns do not touch each other , Acetylcholine (ACh) Acetyl ylch c oline (A (ACh Ch)) • Moveme Movement ment nt physically. separated icallyy. Instead, Insteead, they they are se epa para rate ted by tiny tin i y gaps fille filled with extracellular ed wit i h extra acellular fluid. flu uid id. Since electriellec ectr t ical signals ignals are unable to to jump j mp tthis ju his gap, neurons neurons S Epinephrine ephrine (A (Ad (Adrenalin) dren ena alin n) send chemical messengers chem mical mess sengers rs instead. instead ad.. These The chemiche hemi m - H Epinep cal me messengers called mess sseengers are cal alle led d neurotransmitters (see Norepinephrinee A (N Tablee 4.2) 4.2). ). ((Noradrenalin) oradrenalin) ● Figur Figure re 4 4.6 . iillustrates .6 llus ll u traates the sequence seq quencce of events eveent nts N D opami mine Dopamine triggered action potential ered by b tthe he arrival of an actio on pote tent ntiiall at an nN axon terminal. The neurotransmitters neurotransmiitt tter erss in n the the axon axo xon n O terminal vesicles. The inal are contained in synaptic vesicles arrival of an action potential releases the vesicles N Serotonin from their protein anchors, much like boats leaving a dock, and the vesicles migrate rapidly to the 1 cell membrane. Because the vesicles are made of Glutamate the same thin, oily material as the membrane, 9 GABA they easily fuse with the membrane and spill their 0 contents into the synaptic gap. Following release, Endorphins 9 the vesicles are pinched off the membrane and T refilled. The neurotransmitters released across the synaptic S gap come into contact with special channels on the receiving neuron, known as receptors. Receptors work with the neurotransmitters like locks and keys. Only a neurotransmitter with the right shape (the key) can attach itself, or bind, to a particular receptor (the lock). Neurotransmitters do not stay bound to receptors very long. Once they pop out of the receptor binding site, neurotransmitter molecules either drift away from the gap, are broken down by enzymes, or return to the axon terminal from which they were released in a process called reuptake. In reuptake, special channels in the axon terminal • • • • • • • • • • • • • • Memory Memo mory Autonomic A Au ton to nomiic nervous n r vou ne us syste system function Arousal A rousa al Arousal Vigilance Vigi Vi gila lanc nce nc e Movement Move Mo vement Planning Plan Pl anni n ng Reward R Rewa ewa w rd Mood Appetite Sleep Excitation of brain activity Inhibition of brain activity Pain synapse A point of communication between two neurons. neurotransmitter A chemical messenger that communicates across a synapse. receptor A special channel in the membrane of a neuron that interacts with neurotransmitters released by other neurons. reuptake A process in which molecules of neurotransmitter in the synaptic gap are returned to the axon terminal from which they were released. HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 139 Synaptic vesicles 1 Action potential reaches axon terminal. 6 Vesicles are refilled with neurotransmitter. Axon terminal 4 Vesicles open, releasing neurotransmitters into synaptic gap Neurotransmitter molecules 5 Vesicle material is recycled. 2 Synaptic vesicles are released from their protein anchors. 3 Synaptic vesicles fuse with axon membrane at release sites. Synaptic gap releasse (a) Neurotransmitterr release Cell receiving information Channels used ffor reuptake fo Ne Neu eurot eu e urot rotran rans ran ransm smitter smitter Neurotransmitter urrot rotran otransmitter molecule mol molecule S R Receptors H (b) Reuptake A Figure 4.6 N Chemical Signaling. gnaling g. Be Bec Because cause mostt neurons are se separated epaarated d ffrom rom ro m ea each ch o other theer by th by extracellular extraaceellullarr flu fluid, uid d, tthe hee act action tio on potential pot oten enti tial cannot jump from one neuron neurons, signals uron to the next. To cross the gap between betw wee een n ne neu uron onss, cchemical hemi he miccal N sig gnaals are arre used d instead. insteaad.. (a) (a a) Neurotransmitter Neu uro otra rans nsmitter Release. The arrival of an action potential at the axon terminal triggers a sequence of events neurotransmitter euro rottraansmitter molecules, molecule O that results in the release off neu which float across the Reuptake. h synaptic i gap to iinteract with i h receptors on the h receiving i i neuron. (b) R k After Af iinteracting i with i h receptors, N them to be recycled and used again later. neurotransmitter molecules are often recaptured by the neuron that released membrane allow the neurotransmitters to move back 1 into the releasing neuron, where they are repack9 for later use. Many important drugs, including aged the 0 antidepressant drug fluoxetine (Prozac-), interfere with or inhibit this reuptake process. 9The interaction between neurotransmitters and T receptors can have one of two effects on the their receiving neuron: excitation or inhibition. When S a neurotransmitter has an excitatory effect, it will slightly depolarize the receiving neuron, increasing the likelihood that the neuron will reach threshold and initiate an action potential. Recall that depolarization reduces the difference between the electrical environments inside and outside the neuron. When a neurotransmitter has an inhibitory effect, it will slightly hyperpolarize the receiving neuron, moving the cell farther from threshold and reducing the likelihood that it will initiate an action The “SSRI” label for some antidepressant medications, including Prozac®, stands for Selective Serotonin Reuptake Inhibitor. People who are depressed often have lower than normal serotonin activity at the synapse. If you inhibit reuptake of serotonin, that means more molecules remain in the synaptic gap longer, where they can continue to interact with receptors. Serotonin activity increases, relieving depression, because we get more “bang for the buck” each time serotonin is released. 140 Chapter 4 | THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. © Argosy Publishing, Inc. Receptors M I L E S , © Sue Sue Ford/Photo For o d/P d/ hot o o Researchers, R Rese Inc. potential. Recall that hyperpolarization increases the difference between the electrical environments inside and outside the neuron. Excitatory messages seem logical. One neuron is telling another to “pass the message along.” Inhibitory messages, however, seem somewhat strange at first glance. Why would our nervous systems need a message that says, “Don’t pass the message along”? Tetanus, for which you probably have been vaccinated, provides a dramatic example of what can happen when inhibition doesn’t work properly. The toxin produced by the bacteria responsible for tetanus selectively damages inhibitory neurons in the parts of the nervous system that control muscle contraction. Normally, excitatory inputs that contract muscles coordinate their activity with inhibitory inputs that tell muscles to relax, allowing for the steady hands we need to put in a contact lens, for example. Without the input of the inhibitory neurons, M is the system is left with excitation only, and the result the extreme muscle contraction that gives tetanusI its other name—lockjaw. L Synapses usually occur in many locations on the dendrites or cell body of the receiving neuron, andEthe S depolarizing or hyperpolarizing current that results from neurotran neurotransmitter nsmittter activity at these synapses drifts , to the he junction n of the the cell body dy and and axon. axo xon. n. If If there ther th ee is sufficient fficiient depolarization d po de olarizzation to reach reaach threshold thresh shol old d at tthis hiss hi S junction, the will potential. tion, th he neuron w ill ge il ggenerate neraatee an action n poten ntiall. If not, will remain neuron’s “decision” t, it w ill rema ain at re rest. The n euron’ eu n’ss “d “decis sH ion” io to generate potential ner eraate an action p otential or not is referred to as Ap summation; neuron, matio on; tthe he n eu uro ron, n in otherr words, is adding up Toxins Toxi To x ns from from m the thee bacteria bactterria that ba tha hatt cause caus ca use tetanus travel trave from a all incoming messages making ncomiing m essa es sage g s and maki ing a ““decision” deci de cisi s on on”” based bN ased d woun und to to the nervous nervvou us system, sys yste tem m, where the neurons responsible wound on that hat information. info f rmation. The neuron’ss task task k iss not unlike unl nlik ikeeNth the inhibiting muscle contraction As for in inhibi bitting gm uscl clee co ont ntract ctio i n are selectively damaged. d situation friends family tion we face when we ask fr frie iend nds and and fa fami mily ly ffor or a result, too much mus scl clee co cont ntraction occurs, giving giv muscle contraction tetanus O advice. ce We will receive some excitatory advice (Go for its alternative name “lockjaw” and causing this affected baby’s N it!) along with some inhibitory advice (Don’t even think back to arch. People living in the United States typically about it!). Our job, like the neuron’s, is to sum our input receive vaccinations for tetanus, but the disease still strikes many people worldwide. and make a decision. Unlike us, however, the neuron 1 cannot disregard the advice it receives. 9 Types of Neuro- Researchers have identified0more than 50 different chemicals that serve as neurotransmitters at the transmitters 9 synapse. Table 4.2 lists some of the neurotransmitT and we will highlight ters that are particularly interesting to psychologists, a few of these in this section. In our chapter on consciousness, we explore S examples of psychoactive drugs, both therapeutic and recreational, that interact with the normal biochemistry of the nervous system. Acetylcholine (ACh) is a neurotransmitter found in a number of systems important to behavior. ACh is found at the neuromuscular junction, the synapse at which the nervous system commands muscles. Interference with the action of ACh at the muscles can result in paralysis and death, making drugs that act on ACh popular for use as pesticides and as bioweapons. ACh also serves as a key neurotransmitter in the autonomic nervous HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 141 © Alison Wright/CORBIS system, discussed later in this chapter, which carries commands from the brain to glands and organs. ACh is also intimately involved in the brain circuits related to learning and memory. These brain circuits are the first to deteriorate in Alzheimer’s disease. Not too surprisingly, memory deficits are among the earliest symptoms of Alzheimer’s disease to appear. Among the many drugs that act on ACh systems is the nicotine found in tobacco. Norepinephrine is released in the brain and leads to arousal and vigilance. Consistent with this role in arousal, norepinephrine is also released by the sympathetic division M of the autonomic nervous system, discussed later in this chapter. TheI sympathetic nervous system prepares us to react to emergencies by providing L the resources needed for extra activity, like the extra oxygen that is needed to run or throw a punch. Abnormalities in norepinephrine activity E have been implicated in a number of psychologiS disturbances in arousal and vigilance, including cal conditions that feature stress disorder (PTSD), discussed bipolar disorder and posttraumatic discusse in , chapter on psychological disorders. our chap apte terr o np sych sy cholog ogic ical d isorde is ders rs.. Dopamine Do opamine iiss a neurotransmitter n urot ne otra ranssmitt tteer involved d with wi systems systems that th hatt govern go S movement, normal move eme ment, planning, plan nni ning, and an nd reward. rewa ward rd. Parkinson’s Park Pa rkin i so son’ss disease, dise di seasse, which which h makes makkess no movement difficult, results when dopamine-releasing neurons m oveme ment nt vvery eryy di diffic fficult, t,Hresul ults ts whe hen n do dopa pami m ne-rrel eleasi sing ng n euro ons iin n the participates brain’s movement circuits begin to die. In addition, dopamine particip A ppleasure circuits in the brain’s reward and pl easure cir rcu cuits byy becomingg active whenever when we engage enggage in behaviors beh ehav avio iors rsNthat tha hatt promote prom omo otee survival survviv su ival al and and successful succcessful reproducrepro tion, such su uch ass eating e ting ea i g a great grN eat at meal mea eal or having hav avin ng sex. seex. x Most Mos ostt drugs that produce pro addiction, methamphetamine, increased addictio ion n, iincluding ncclu ludi dingg ccocaine ocaiine and oc nd m etha hamp mpheta tami mine ne, st sstimulate imulate incre O circuits. In our chapter on p psychological disorders, activity in dopamine circuits syych chological disor These residents of the Amazon basin are preparing darts with curare, a chemical derived from plants that causes paralysis by blocking receptors for acetylcholine (ACh) located on muscle fibers. When the receptors are blocked, the muscle is unable to respond to o messages from m the nervous system, leading paralysis. em, lead adin ing g to p aralysiis. N 1 9 0 9 T S © Originally used to help children with crossed eyes, Botox is now a popular, but temporary, way to reduce facial wrinkles. 142 Chapter 4 | THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. © Philippe Psaila/Photo Researchers, Inc. M I L E S for endorphins, our natural This image highlights areas of the human brain that are rich in receptors opiates. s. The red areas have the most endorphin receptors, followed by the yellow areas. Opiate , with these drugs, such as heroin or morphine, morrphine, affect our behavior beh ehav avio ior byy interacting int nter erac a ting g with thes ese receptors. recept ptor orss. The The red areas in image thalamus. n thee center cente terr of tthe he ima age are located d in n the thalam muss. S we wil will ll se see ee how disr disruptions ruption ns to dopamine dop opam amin ine ci circuits irc rcui u ts have beeen implicated be imp mpli lica cate ted d in in H been schizophrenia oph phrenia and attention attte tent ntion deficit hyperactivity disorder (ADHD). A sleep, appetite, Serotonin eroto oni nin n is involved inv nvol olved with systems syystems regulating appet etiite, and mood. Consequently, threee beha behaviors linked. As we d. Co onseq equeent n ly, these th avi vior orss ar aree tightly tigh ti ghtl l y l ink nked ed. we will will N see in psychological disorders, n ourr chapter chapter on psycholo ogical di diso sord rder ers, s, people pNeo eople who who o experience exxperrieence ce depressed essed mood also show abnormalities abnorrma mali litiies in in appetite appe ap peti titee and and sleep. sleep ep. Sleep p deprivation can result in changes in mood O and appetite, Botox-, which whic wh hicch iss used to treat muscle m N Penev, & spasms or reduce wrinkles, is made from even leading to significant overeating (Spiegel, Tasali, Van Cauter, 2004). an inactive form of the toxin responsible Endorphins (short for “endogenous morphine,” or morphine 1 to pain. for botulism, which is produced by produced by the body) modify our natural response 9 to have a bacteria that spoil food. Botox interacts In evolutionary terms, it makes a great deal of sense with ACh by preventing its release from system that will reduce your chances of being disabled 0 by pain during an emergency. All too frequently, however, we under- the axon terminal. Without the activity estimate the extent of our injuries until we wake9up the next of ACh telling a muscle to contract, the T ” in which muscle remains paralyzed. morning feeling very sore indeed. “Runner’s high, people who regularly engage in endurance sports S experience a sense of well-being and reduced sensation of pain, is probably due to the release of endorphins initiated by high levels of activity. Opiate drugs such as morphine, heroin, and Oxycontin. produce their pain-relieving effects by mimicking the action of endorphins at the synapse. In other words, the opiate drugs are so similar in chemical structure to our natural endorphins that the receptors cannot tell them apart and treat the opiates as if they were natural endorphins. HOW DO NEURONS COMMUNICATE? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 143 Summary 4.1 Neural Communication © Peter Fromherz/ Max Planck Institute of Biochemistry Myelin Axon Axon Myelin Resting 40 mV 2 Action potentials 1 Sodium channe nels open; channels sodium rushes in. 2 Potassium channe channels nels open; potassium starts to leave cell. 3 Sodium channels cclose. lose. 4 Potassium channelss close. 0 1 Depolarization shold ential 4 –65 –70 Hyperpolarization 0 1 2 Time (in n msec) m 3 Depolarizing input © Omikron/Photo Researchers, Inc. The sy Th syna synapse naps pse e © Philippe Psaila/Photo Researchers, Inc. Neurotransmitters 144 Chapter 4 | • Neurons receive information on their dendrites and send information via their axons. M I L E S , • Hold neurons in place • Clean up debris • Blood-brain barrier • Formation of myelin • Without incoming signals, cell has a resting restin ng potential. potentia al. LLearning arn ning 2013 © Cengage Le Resting (b) Glia outside the brain and spinal cord Refractory period Glia © Argosy Publishing, Inc. Axon 3 and carry out most “housekeeping” functions. Dendrite Axon Action potential • Cell bodies contain the nucleus Axon Myelin Glia What to remember The neuron Cell body Glia (a) Glia in the brain and spinal cord Feature S H A N N O N 1 9 0 9 T S • When Wh hen ccell ell rea el reaches ach hes th thre threshold, resh shold d, a an n acttion on potential pot o entia al occurs. occurss. action • Action Actition pot Ac potentials ten entials ar are e fo foll followed llowed ed b by y refractory periods. • Action Actition Ac o pot potentials ten entitial alss ar a are e propagated dow do wn the e axon axo on to the the terminal. down • A sy synapse yna aps pse is a p point oint of commun niccat atio ion n between two communication neurons. • When an action potential arrives at a terminal, neurotransmitters are released. • Neurotransmitters interact with receptors in the receiving neuron’s membrane. • Neurotransmitters remaining in the synaptic gap are deactivated. • Acetylcholine • Norepinephrine • Dopamine • Serotonin • Endorphins THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. How Is the Nervous System Organized? 0.2 7 65 First Homo sapiens First Hominins Extinction of the dinosaurs 500 First brains © Cengage Learning 2013 Millions of Years Ago Nervous systems are fairly recent innovations that separate animals 700 First simple nervous from plants. We can place the origin of Earth at 4.5 billion years systems ago and the first single-celled life forms 1 billion years later, but the first neural nets appeared only 700 million years ago. In these primitive animals, the nerves in the abdomen were just as likely to be important to behavior as the ones in the head. True brains residing in heads did not appear until animals formed skeletons, around 500 million years ago (● Figure 4.7). The first decidedly human brain made its appearance only 7 million years ago, a small blip in the timeline of evolution (Calvin, 2004). TheMcurrent model of the human brain has only been available for theI last 100,000 to 200,000 years. As neural nets led to true brains, culminatingLin the modern human brain, capacity for behavior changed accordingly. Just as E your cell phone can perform more complex functions than most S 20th-century computers, human nervous systems brought a com, i ns. Al plexity behavior unimaginable previous versions. Although ty to behav vior u nimaginable ffor or p revi viou ouss vers rsio A thou ugh a worm’s ability rm’ss abi bili lity tto o usee its neurall net net to find d good tthings hiing ngs tto o eat at aand nd d avoid creatures good we have d crea atu turres that th hat consider con nsi sider it go ood to eat at iiss impressive, impres essi s ve, ve h av v e S evolved that no study ved d a nervous system sy nott on only l aallows lllow ows you yo ou to stu udyy tthis hiss hi 3,370 0 First sin Fir single gle-c -c single-celled textbook psychology but ook k aand nd get an n A in your psych hology course H b ut also guides guide d s organisms A & Decety, you through hroug ugh h the t e maze th maz that is human hum man social life (Cacioppo Decetty, 2011;; Dun Dunbar Schultz, nbarr & Schultz tz, 2007). N prepared now out We aree p repared re dn ow to zoom mo ut from from tthe he sstructure tru tr uctu ture aand nd funcfun nction of the neuron to examine th this hiss larger lar arge gerr view: view vi w: the theNstructures strructturess and and O the behavior systems ms constructed from billions of neurons and they produce. Talking about the connections between N the structions of the nervous system and behavior requires a quick word The Earth forms 4,500 of caution. Just as saying that we have a “gene for” a behavior is 1 overly simplistic and inaccurate, here we want to remind ourselves that saying we have a “center for” a behavior in the9brain is equally F i g u r e 4 . 7 misleading. Although we can identify structures that participate 0 intricate and in certain behaviors, the biology of mind involves Timeline of Brain Evolution. Brains are a 9 connected fairly recent development in the history of overlapping patterns of activity involving many richly evolution, appearing about 500 million years structures. T The nervous system can be divided into two major compo- ago or 3 billion years after life first emerged S nents: the central nervous system (CNS) and the peripheral ner- on earth. vous system (PNS) (● Figure 4.8). The central nervous system consists of the brain and the spinal cord, which extends from the brain down the central nervous system (CNS) The back of the body. Although we often see the brain and spinal cord referred brain and spinal cord. to as separate structures, it is important to note that they form one con- spinal cord A long cylinder of neural tinuous unit of tissue. Nerves branch outward from the CNS to all areas tissue extending from the medulla of the of the body—the lungs, heart, and other organs, the eyes, ears, arms, legs, brain down to the middle of the back; part of the central nervous system. fingers, and toes. As soon as a nerve branches outward from the CNS, it is HOW IS THE NERVOUS SYSTEM ORGANIZED? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 145 Figure 4.8 THE NERVOUS SYSTEM Peripheral nervous system (PNS) Central nervous system (CNS) Brain Spinal cord Somatic nervous system M I L E S , S H A N N O N Autonomic nervous system Sympathetic nervous system Pa Par arasy assympathetic a asy Parasympathetic ner n rvo vous system m nervous © Argosy Publishing, Inc. The Organization of the Nervous System. The nervous system has two major divisions, the central nervous system (CNS), containing the brain and spinal cord, and the peripheral nervous system (PNS), containing all nerves that exit the brain and spinal cord. The CNS is protected by bone, but the PNS is not. 1 considered part of the peripheral nervous system. Another way to know 9 you have left the CNS for the PNS is to look for the protection of bone. 0 Nerves of the CNS are encased in bone, but those of the PNS are not. 9 T S peripheral nervous system (PNS) The nerves exiting the central nervous system that carry sensory and motor information to and from the rest of the body. 146 Chapter 4 | What Are the Structures and Functions of the Central Nervous System? The brain and spinal cord are among the best-protected and most wellsupplied parts of your body, which is not surprising given their importance for your survival. Although the brain makes up only about 2% of your total THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 1 9 0 9 T S Fourth ventricle Figure 4.9 The Ventricles of the Brain. The ventricles of the brain are filled with circulating cerebrospinal fluid (CSF), which floats and cushions the brain. Meningitis is an infection of the membranes surrounding the central nervous system, or meninges. If you g whyy yyour college were wondering obtain for asked you yo ou to o btain n a vaccination vacc va cc mening ngit itiis, th this is is what wh ca meningitis, can happen if contract disease. yyou ou co contra act tthe he di isease. © Bart’s Medical Library/Phototake ry/Ph ry /Photo ototak ake e Third Third ve entricle ent en ventricle S H A N N O N © Argosy Publishing, Inc. La ateral ventricles es Lateral Courtesy of Cincinnati Children’s Hospital Medical Center body weight, it is the target of about 20% of the blood pumped by the heart. Surrounding the brain and spinal cord are the heavy bones of the skull and spinal vertebrae. Just under these bones, membranes known as meninges provide further protection. Infections of these membranes result in potentially life-threatening cases of meningitis, for which you have likely been vaccinated prior to beginning your college studies. The brain and spinal cord are further protected by a clear, plasma-like fluid known as cerebrospinal fluid (CSF). CSF seeps out of the lining of hollow spaces in the brain known as the ventricles (● Figure 4.9). Near the base of the skull, openings enable CSF to flow from the ventricles into a space within the meninges, allowing the fluid to flow around the outer surfaces of the brain and spinal cord. Without the cushioning provided by the CSF, a blow to the head would cause considerable damage to the brain. In addition, the CSF “floats” the brain within the skull, preventing any false signals that might result from the weight of some M neurons pressing down I on others. To diagnose some medical conditions, it is helpful L to obtain a sample of CSF. This is done through a spinal tap, in which a physician removes some of E the spinal cord. CSF the CSF circulating through the meninges surrounding S is constantly produced, so any blockages in its circulation cause the fluid to build result uild up. Thee resu ult is hydrocephalus, which means water on the brain.” , “water When blockages occur in the circulation of cerebrospinal fluid, a condition known as hydrocephalus occurs. The word hydrocephalus comes from the Greek words for “water” and “head.” Before modern treatments became available, babies like this one would usually experience cognitive deficits. These blockages are now identified at birth and can be treated surgically or by installing a shunt to drain off excess fluid, avoiding the damage that would otherwise occur to the brain and preserving the child’s intelligence. WHAT ARE THE STRUCTURES AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 147 The spinal cord extends from the lowest part of the brain down into the middle of your back (● Figure 4.10). If you feel the back of your skull where it curves to meet your spine, your fingers will be just below the junction of the spinal cord and the lowest structure of the brain. Although the spinal cord comprises only 2% of the weight of the central nervous system, its functions are vital, as evidenced by the challenges faced by people with spinal damage. The spinal cord serves as a major When the cushioning disks separating conduit for information flowing to and from the brain along the vertebrae are damaged or the bones large bundles of axons, carrying sensory information from the are misaligned, the resulting pressure body and delivering commands. Thirty-one pairs of spinal nerves exit the spinal cord to serve the body. These nerves exit of bone on spinal nerve can produce the and enter the spinal cord between segments of the bony verteexcruciating pain of a “pinched” nerve. brae in your spine. M A number of important reflexes are initiated by the spinal cord without I One type of spinal reflex will make you pull your the assistance of the brain. body away from any source L of pain. It doesn’t take long for your hand to fly up when you’ve touched something hot on the stove. When your docE tor taps your knee with a hammer during a routine physical, he or she is The Spinal Cord, Brainstem, and Cerebellum S , S H A N N O N Connecting to Research The Discovery of Mirror Neurons I n the early 1990s, a team of Italian scientists led by Giacomo Rizzolatti were busy studying the brain correlates of movement when they noticed something odd (Di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992). They had observed that certain neurons in a part of a monkey’s brain became especially active when the monkey performed certain actions, like reaching for a piece of banana or a peanut. When an experimenter picked up a piece of food to place it within the monkey’s reach, some 148 Chapter 4 | 1 of the same neurons began 9 to fire. Suspecting something important 0 was behind these observations, the 9 these researchers began to study “mirror neurons” moreTcarefully. The Question: Can we identify neurons S that respond to a particular action, regardless of who performs the action? METHODS A monkey (Macaca nemestrina) served as the research subject. The technique used in this experiment was single cell recording (see Table 4.1), in which surgically inserted microelectrodes allowed the activity of individual cells to be measured. A total of 184 neurons were tested by observing their activity during the monkey’s own movements and during movements performed by an experimenter. The experiments were videotaped. The experimenters also recorded the muscle movements in the monkey’s hand and arm. RESULTS Thirty-nine of the observed neurons appeared to be most active when either the experimenter or the THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Gray matter (cell bodies) White matter (axon pathways) © Argosy Publishing, Inc. Spinal nerve Vertebra M I L E S , S H Figure 4.10 A The Spinal pinal C Cord ord a and nd th the Spina Spinal al Nerves. Thirty-one Th hirtty-onee pairs pai airs rs of of sp spin spinal inal al nerves nN errvees eexit xiit b between etwe et ween n tthe he bon bones ones es o off th the he ve vert vertebrae teb bra rae to bring senso sensory ation ba back ck tto o the cent ntrral nervous syst tem and d to o carry carr ca rryy motor moto mo tor commands comm mmands to to muscles. musscles. information central system N O N CONCLUSIONS The scientists believed they had discovered neurons that provided a mechanism for understanding the 1 9 0 9 T SThese cells are actions of others. When a monkey reaches for a banana itself or sees someone else reach for the fruit, some of the same neurons in the brain become active. Giacomo Rizzolatti and his colleagues named these “mirror neurons.” now referred to as “mirror neurons” (Caggiano, Rizzolatti, Pomper, Thier, Giese, & Casile, 2011). Although the existence of mirror neurons in humans is still controversial, this discovery stimulated new hypotheses regarding imitation, autism, and empathy. E WHAT ARE THE STRUCTURES AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. © Dan Herrick/Alamy monkey performed the same action. The cells’ responses were very specific. For example, a cell that became active when the experimenter grasped a piece of food would also become active when the monkey grasped the food, but not when the monkey put food in its mouth. A cell that activated when the experimenter put food in his mouth also activated when the monkey put food in its mouth, but not when the monkey grasped the food. 149 Figure 4.11 Checking Spinal Reflexes. When your physician taps on your knee, your thigh muscle stretches. Information about the stretch is carried to the spinal cord by a sensory nerve. The spinal cord sends a command to the muscle to contract to counteract the stretch, and your foot kicks out. The spinal cord manages this reflex alone. No higher level of processing in the nervous system is necessary for this reflex to occur. © Argosy Publishing, Inc. 1 Hammer tap stretches thigh muscle. 5 Foot Fo t Foo kic cks. kicks. brainstem The part of the brain containing the midbrain, pons, and medulla. medulla The brainstem structure that lies just above the spinal cord. 150 Chapter 4 | checking another type of spinal reflex, the knee-jerk reflex (● Figure 4.11). This reflex is interesting to your doctor, because certain medical conditions, such as diabetes, affect the strength of the reflex. Still other spinal reflexes help us stand and walk. Spinal reflexes give us an 2 Sensory fibers sense opportunity to look at the funcincreased stretch. tions of three different types of Sensory neurons. Sensory neurons carry To brain fiber information from the external Thigh muscle environment or from the body M back to the CNS. In the knee-jerk I reflex, sensory neurons tell the spinal cord that a muscle has been L stretched by the tap of the hamE mer. Motor neurons carry comMotor Spinal fiber cord S mands from the CNS back to the muscles and glands of the body. bod In fibers 3 Sensory , stimul sti m ate mo motor stimulate information about response re se to info form rmat atio i n ab abou ou the neuro neu ons in the th he neurons 4 Motor neurons neuron rons stretched muscle, spinal cord stretche hed d musc scl l e, , the sp p in n al spinal cord. sp spi nal co na cord d. cause thigh h S muscles to o ssends se ndss a message nd messsag me age through throu th ugh h motor m contra con tract. contract. neurons back to leg, telling neur ne r o ns ba c t o your yo ur leg eg, , te H the muscle to contract to ccounA teract the stretch. stretch h. You know what N happens happ appen ens next—your next ne xt—y —yyour foot kicks kick as muscles Neurons the h musc mu c les le s contract. Neu N have neither sensory motor functions interneurons. that hav avee n eit ithe her se sens nso oryy nor m oto tor fu func nction ons ar aree ca called interneu O“between” ” as many interneurons Inter in this case means “between, inte tern rneeurons form bridges bri N neurons. The knee-jerk reflex forms a very between sensory and motor simple arc between a sensory neuron and a motor neuron and does not require any interneurons. However, interneurons play important roles in 1 more complex reflexes and throughout the nervous system. Moving up from the 9 spinal cord brings us to the brainstem. Early in prenatal development, the emerging brain forms three bulges. The most for0 ward of these bulges will develop into the two large cerebral hemispheres, 9 which we discuss in a later section. The remaining two bulges form the T ● Figure 4.12, you can see that the brainstem brainstem. If you examine looks like a stem of a flower, S supporting the larger blossom of the cerebral hemispheres. Directly branching from the brainstem are the cranial nerves, which perform the same functions for the head and neck areas that the spinal nerves manage for the remainder of the body. We will discuss the cranial nerves in more depth in a later section on the peripheral nervous system. The spinal cord merges with our first brainstem structure, the medulla. Like the spinal cord, the medulla contains large bundles of axons traveling to and from higher levels of the brain. Because the medulla manages many THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. © Argosy Publishing, Inc. © Charlie Neuman/ZUMA Press/Corbis orbis Figure 4.12 essential functions, such as heart rate and blood pressure, damage to this structure usuStructures of the Brainstem. The brainstem contains structures ally results in quick death. responsible for reflexive behaviors, heart rate and breathing, arousal Just above the medulla is the pons, which and sleep, preliminary sensory analysis, and balance and movement. contains structures involved with the management of sleep, arousal, and facial expressions. Pons means Cerebral “bridge” in Latin. The pons cortex not only serves as a bridge between higher and lower portions of the brain but also connects the cerebellum to the rest of the brain. Thalamus Essential for maintaining M balance and motor coorI dination, the cerebellum is Midbrain one of the first structures L in the brain to be affected E Cerebellum Pons by alcohol. As a result, alcoSReticular hol consumption impairs balance (walking a straig straight ight line) and ,formation motor your or coordination coordinaati t on (touching (touchin ng you ourr fingerr to o the ttip ip of of your you ur nose with th your Me M dulla Medulla S Med eyes closed). sobriety tests the closed) d). Most sob obriiet e y test stss are th he samee ttests neurologist would use ests ts a neurolo logist w ou uld u se to to assess asse sess ss the the H function tion ti on of the cerebellum. cerebe bell llu um. A Because on the brainstem, ecaus use of of the he cerebellum’s cer ereb e ellum’s position po which relatively h is rela ativvel elyy ancient an ncient in terms terrms of of evolution evol ev olut utio oN n comcom pared hemispheres, neuroscientists initially d to the h cerebral hemisphere es,, neu uro roscie ient ntiists tsN in nittiallly underestimated restimated its importance to human hum uman an behavior. beh ehav avio ior. They O Th y believed ved that the cerebellum’s activities were restricted to N we managing the timing and strength of movements. While still do not know exactly what the cerebellum does, today’s scientists believe that it has a broader role in making men1 tal and motor skills more automatic. Damage to the human 9 cerebellum produces subtle deficits in language, cognition, and perception. In autism, a condition that affects 0 language, sensory, and social behaviors, abnormalities in the 9 cerebellum are very common (Courchesne, 1997). T cells Surprisingly, the cerebellum contains more nerve Most sobriety tests actually assess the function of the than the rest of the brain combined. Not only doesS the cercerebellum, which helps us maintain balance and muscle ebellum contain huge numbers of neurons, but it is richly coordination. connected with the rest of the central nervous system. The cerebellum receives input from approximately 40 million nerve cells located at the highest levels of the brain (Leiner, Leiner, & Dow, pons A part of the brainstem located between the medulla and midbrain. 1991). To put that number into perspective, each eye sends input to the cerebellum A structure attached to brain from only 1 million nerve cells. In turn, the cerebellum sends vast the brainstem that participates in skilled amounts of information back to higher levels of the brain as well as to the movement and, in humans, complex cognitive processing. pons, medulla, and spinal cord. WHAT ARE THE STRUCTURES AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM? 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. 151 The midbrain sits above the pons and contains a number of structures involved in sensory reflexes, movement, and pain. For example, the periaqueductal gray of the midbrain plays an important part in the body’s management of pain because it contains receptors for endorphins. When endorphins are present in the periaqueductal gray, they reduce the perception of pain by decreasing the strength of pain messages travelOpiate painkillers like morphine and ing up the spinal cord to higher levels of the brain. Oxycontin- produce some of their Running the length of the brainstem’s core from the upper analgesic effects by interacting with medulla into the midbrain is the reticular formation, which participates in the control of mood, arousal, and sleep, disopiate receptors in periaqueductal gray. cussed further in our chapter on consciousness. The neurons in these areas are the source of most of the serotonin and norepinephrine in the brain. As a result of the actions of the reticular formation, we are able to respond differently to the world as a function of our state of arousal. The M attention in a quiet library will be completely same sound that grabs your I asleep. ignored while you are sound L Embedded within the vast tracts of white matter E make up the bulk of the cerebral hemispheres that are S a number of subcortical structures that participate in self-awareness, learning, emotion, movement, communication, communication the , inhibition off im impulses, the regulation Wee call inhibitiion o mpu p ls lsees, an and th he regu gula lati tion on of body bo states. sta tate tes. s W ll tthem “subcortical” because means “below, cerebral “subco cort rtical” be ecaause they th hey lie lie i sub, su which wh mean anss “b “below ow,” the cer reb bral corS tex, w which comprises wrinkled outermost hich com mpriises tthe he w rin ri nkleed ou oute t rm rmos ostt covering coveri co ring n of of thee cerebral cer hemispheres. hemisp phe here ress. H Early anatomists collected some of these subcortical structures into in a A “border,” aand limbic system syystem (limbic means nd these structures form a gentle g curve be cerebral cortex), below w th thee ce cere rebr bral aN cor orte tex) x), bu but th thiss tterm erm er m is losing los osin in ng popularity with contemporary anatomists. contem mporaary ana nato tomi m sN ts. You u might migght also also o have haave heard hea eard rd the limbic system sy referred “your ed tto o ass “yo yourr emotional emo motiional brain. brain in.” As As you yo will w ll see wi see in in the next few secO including some form tions, structures, formerly limbic tions subcortical structures mer e ly l listed in the li N in our emotional life, but they perform many system, do indeed participate other functions as well. We usually discuss these structures in the singular, as in “thalamus” or “hippocampus,” but they actually are paired sets of 1 structures, one on either side of the brain. Subcortical Structures midbrain The part of the brainstem that lies between the pons and the cerebral hemispheres. reticular formation A collection of structures located along the midline of the brainstem that participate in mood, arousal, and sleep. thalamus A subcortical structure involved with the processing of sensory information, states of arousal, and learning and memory. basal ganglia A collection of subcortical structures that participate in the control of movement. hypothalamus A subcortical structure that participates in the regulation of thirst, temperature, hunger, sexual behavior, and aggression. 152 Chapter 4 | 9 The Thalamus Just about 0 at the very center of the brain lies the thalamus. The thalamus is often referred to as the “gateway to the cortex,” as input 9 from most of our sensory systems (vision, hearing, touch, and taste) travels T then forwards the information along to the first to the thalamus, which cerebral cortex. The cortex, S in turn, forms large numbers of connections with the thalamus. In addition to its role in sensation, the thalamus is involved with memory and states of consciousness. Lesions in the thalamus are associated with profound memory loss (Cipolotti et al., 2008). As you will learn in a later chapter on consciousness, during our deepest stages of sleep, the thalamus coordinates the activity of cortical neurons, “tuning out” the outside world and making it more difficult to be awake. Disturbances in the circuits linking the thalamus and the cortex accompany some seizures. THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 9781305461994, Discovering Psychology: The Science of the Mind, Cacioppo/Freberg - © Cengage Learning. All rights reserved. No distribution allowed without express authorization. Figure 4.13 Thalamus Basal ganglia The Basal Ganglia The basal ganglia are a collection of large structures involved with voluntary movement that curve around to cup the thalamus (● Figure 4.13). The basal ganglia receive substantial input from all areas of the cerebral cortex and from motor structures located in the brainstem. In turn, the basal gan- M glia send information to the cortex. I Degeneration of the basal ganglia occurs inL Parkinson’s disease, a condition that makes the iniE tiation of voluntary movement extremely difficult. Involvement of the basal ganglia is also suspected S in a number conditions ber of cond dition ns that we will encounter in our, later chapter psychological disorders, obsessiveter on psych c olo ogical disorde derrs,, including includ in udiingg ob bse sessivvecompulsive deficit pulsi sive disorder dis i orrder (OCD) (OCD) and d attention at deeficitt hyperactivity hyp yper ype yp eeract acttivvity ty S d by iinaddisorder der (ADHD). (AD ADHD D). These Thes Th ese disorders disord derrs are characterized ch haracteerize zed naadequate movement. off OCD OCD, te control con ontrol of voluntary vo olu luntarr y move eme ment nt.. In the he ccase aseeH o CD, patients ntss may endlessly endlesssly repeat a behavior, such h as hand washing, while voluntary movements hing, w hile iin hi n AD ADHD, volunt ntary movemen ntsAcan be unusually nusuaally frequent, frequ quent, t, rapid, and d impulsive. impu uls lsiv ivee. Children Child hi dN reen with the h hyperactivity attention deficit disoryperactivity type of att ten ntion nd efici ficitt diso d i oNr-der are re often described as “driven n by by a motor. moto mo tor.” Amygdala Anteri erior eri or Anterior cin ngu gul u ate ...
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