Chapter 3: The biologicalbases of behavior
3.1 Communication in theNervous System
*Identify the various parts of theneuron and the main functions of glial cells.
Neuronsconsist of soma, or cell body, dendrite, axon, myelin sheath, neurotransmittersand synapse. The soma contains the cell nucleus and much of the chemicalmachinery common to most cells. Dendrites are the parts of a neuron that arespecialized to receive information. Information flows into the cell body andthen travel away from the soma along the axon, which is a long, thin fiber thattransmits signals from the soma to other neurons or to muscles or glands. Axonsare encased by myelin sheath which is insulating material. The axon ends atneurotransmitters which are small knobs that secrete chemicals. The pointswhere neurons interact are called synapses, which are junctions whereinformation is transmitted from one neuron to another.
Glialcells serve a variety of functions. They could provide nourishment for neurons,help remove neurons’ waste products, provide insulation around many axons.Myelin sheaths are derived from special types of glial cells and glial cellsare essential in the development of the nervous system in the human embryo.Recent researches have shown that glial cells may also send and receivechemical signals, some types of glial cells can detect neural impulses and sendsignals to other glial cells, some types can give feedbacks to neurons.
*Describe the neural impulse, andexplain how neurons communicate at chemical synapses.
Thereare two stages for a neuron, at rest or active. When a neuron is at rest,positively charged sodium and potassium ions and negatively charged chlorideions flow back and forth across the cell membrane but are not at the samespeed. The result is that negatively charged ions concentrate a bit more insidethe cell. The resting voltage is called the resting potential which means thestable, negative charge when the cell is inactive. The action potential is onthe contrary a term for the very brief shift in charge. When the neuron isstimulated, channels in the cell membrane open for the positively charged sodiumions to come in and the neuron’s charge becomes less negative and thenpositive, creating an action potential. This is the process of a neuralimpulse.
Chemicalsto transmit information from one neuron to another is called neurotransmitters,which are stored in the synaptic vesicles which are small sacs. With thearrival of an action potential, the neurotransmitters are triggers to releaseto the synaptic cleft, which is a microscopic gap between the terminal buttonof one neuron and the cell membrane. The neurotransmitter released from thepresynaptic neuron diffuse across the synaptic cleft and then certain receptorsites recognize the neurotransmitters and respond accordingly. This is how thetwo neurons communicate.
*Discuss some of the functions ofacetylcholine, the monoamine neurotransmitters, GABA, and endorphins.
Acetylcholine(ACh) is the only transmitter between motor neurons and voluntary neurons, andis responsible for attention, arousal, and memory. ACh is relevant toAlzheimer’s disease. Although it is not the most important reason for thedisease, it does help when amplifying ACh activity.
Thereare three monoamine neurotransmitters, namely dopamine, norepinephrine, andserotonin. Dopamine (DA) is used by neurons that control voluntary movements.The lack of DA could cause Parkinson’s disease. Serotonin contribute to theregulation of sleep and arousal. It has been proved that serotonin is relatedto aggressive behavior. Lower level of norepinephrine and serotonin synapsescould lead to depression. Eating disorders could be a result of abnormalitiesin serotonin circuits.
GABAproduces only inhibitory postsynaptic potential at nearly all synapses. GABA isinvolved in the regulation of anxiety and GABA circuits contribute to themodulation of sleep and arousal.
Endorphinsare internally produced chemicals that resemble opiates in structure andeffects. The endorphins and their receptors are responsible for the modulationof pain and the regulation of eating behavior and the body’s response tostress.
3.2 Organizationof the Nervous System
*Distinguish between the centralnervous system and the peripheral nervous system.
Thecentral nervous system (CNS) consists of the brain and the spinal cord. Thecentral nervous system can be subdivided into the spinal cord and the brain. Theperipheral nervous system is made up of all those nerves that lie outside thebrain and the spinal cord. The peripheral nervous system can be subdivided intothe somatic nervous system and the automatic nervous system. The brain is likea control system for relatively complex information and the spinal cord acts asa bridge between the brain and the peripheral nervous system. The peripheralsystem is responsible for motion and the sensory of the surroundings. Most ofthe activity in the peripheral is automatic and beyond our consciousness.
3.3 Then brainand behavior
*Describe how lesioning, electricalstimulation, and various brain-imaging procedures are used to investigate brainfunction.
Theprocess of inserting an electrode into a brain and exerting a high-frequencyelectric current to destroy the issue around is called lesioning. By electricalstimulation, a weak electric current is sent into a brain to stimulate it.
Brain-imagingprocedures includes computerized tomography scan (CT), magnetic resonanceimaging scan (MRI), position emission tomography scan (PET) and functionalmagnetic resonance imaging (fMRI). The CT scan is an application of X-rays. MultipleX rays are shot from different angles by the control of the computer and thesignals feedback to the computer and finally an image of the horizontal sliceof the brain is provided. The MRI scan uses magnetic fields, radio waves andcomputer to get a 3D image of the brain. The PET scan uses radioactive markersto locate chemical activity in the brain. The fMRI identifies blood flow andoxygen consumption in the brain by using several new variables of MRI.
*Know the principal functions ofkey structures in the brain.
Thebrain could be divided into three parts: the hindbrain, the midbrain and theforebrain. The hindbrain consists of the cerebellum, the medulla and the ponsthat are in the lower part of the brainstem. The cerebellum is responsible forthe coordination of movement, the sensation of our limbs, the sense ofequilibrium, and physical balance. The midbrain is involved in interactingsensory processes. Importantly, the system of dopamine-releasing neurons is locatedin the midbrain, which concerns higher brain center activities and thevoluntary movements. The structure that connects the midbrain and the hindbrainis called the reticular formation, which is responsible for the modulation ofmuscle reflexes, breathing, and pain perception, the regulation of sleep andwakefulness. The forebrain consists of various structures including thethalamus, hypothalamus, limbic system and cerebrum. The thalamus is related tosensory information as it integrates information from various senses. Thehypothalamus is responsible for the regulation of the basic biological needs.The limbic system is known as the seat of emotion. The medial forebrain bundlelocated here is rich in dopamine-releasing neurons. The cerebrum is believed tobe essential for complex thought, such as comprehending speech and language.
*Identify the four lobes in thecortex and their key functions, and summarize evidence of the brain’splasticity.
Lobesare the parts of each cerebral hemisphere. The occipital lobe is at the back ofthe head which is involved in visual activities. The primary visual cortex islocated here. The parietal lobe is in front of the occipital lobe. The primarysomatosensory cortex here is responsible for the sense of touch and position.The temporal lobe is below the parietal lobe and there is an area that isinvolved in auditory processing, which is called the primary auditory cortex.The frontal lobe is the largest lobe in the brain. The frontal lobe containsthe principal areas that control the movement of muscles, which is called theprimary motor cortex. Different parts of the cortex are in control of differentmuscles and the amount of motor cortex involved depends on the diversity andthe precision that the movement requires but not the size of the part.
Thereare three reasons to ensure the plasticity of the brain. First, throughexperience the brain structure could be changed. This could be proved bylooking at the difference of brain structure between a new taxi driver and thedriver who has been familiar with the map of the city. Second, the damage ofthe brain could lead to reorganization of the brain. Blind people develop theoccipital lobe to compensate for the lack of visual experience. Third, newneurons could be generated in the adult brain. These three aspects showevidence of the plasticity of the brain.
3.4 Rightbrain/left brain: cerebral specialization
*Explain how spilt-brain researchchanged our understanding of the brain’s hemispheric organization.
Inspilt-brain surgery, the bundle of the fibers that connects the cerebralhemisphere (the corpus callosum) is cut to reduce the severity of epilepticseizures. This surgery gives scientists opportunity to investigate the functionand connection of the two hemispheres. Each hemisphere’s primary connectionsare to the opposite side of the body, which means that the left hemispherecontrols the right part of the body and the right hemisphere controls the leftpart of the body. Vison and hearing are more complex as the signals come fromone part of the organism go to both two hemispheres. People don’t notice thisorganization in the brain because the two parts work together to betterperceive the information.
*Describe research on cerebralspecialization in normal subjects and what this research has revealed.
Asit is difficult to find subjects with a split-brain, methods have been createdby scientists to look into the different functions and the relationship of thetwo hemispheres. One method is called perceptual asymmetries, which involveslooking at left-right imbalances in visual or auditory processing. As thesignal only comes from one side of the body, subtle difference from the two hemispherescould be recognized in normal individuals by precisely detecting how long ittakes for the subjects to recognize different types of signals. Researchersalso rely on brain-imaging studies that could vividly show the differences intwo parts of the brain to investigate. The studies agree with the ideas ofprevious study, showing that the two hemispheres of the brain are specializedwith certain cognitive tasks. The left hemisphere is usually better at verbalprocessing, such as language, speech, reading and writing, while the righthemisphere shows greater abilities in nonverbal processing, such as spatial,musical, and visual recognition tasks (including the perception of emotions).Apart from the different specialization, researches also show that the two hemispheresof the brain do collaborate constantly to deal with the complicated informationreceived from the outside world.
3.5 TheEndocrine System: another way to communicate
*Identify the key elements of theendocrine system, and describe ways in which hormones regulate behavior.
Theendocrine system consists of glands that transport chemicals into thebloodstream that help control bodily functioning. Hormones refers to themessengers in this communication network, which are the chemical substancesreleased by the endocrine glands. The endocrine system consists of pinealgland, hypothalamus, pituitary gland, parathyroid glands, thyroid gland,thymus, liver, adrenal gland, pancreas, kidney, placenta (in female duringpregnancy), ovary (in female), testis (in male). The pineal gland releases agreat variety of hormones that transport within the body, stimulating actionsin the other endocrine glands. The hypothalamus sends signals to the adrenalglands along two pathways. One is through the autonomic nervous system and theother is through the pituitary gland. Oxytocin is a hormone that is released bythe pituitary gland and regulates reproductive behaviors. This hormone is knownto stimulate contractions when a woman gives birth and to stimulate the mammaryglands to release milk for breastfeeding. New researches also show that thishormone is important for complex social behavior.
3.6 Heredityand behavior: is it all in the genes?
*Describe basic structures involvedin genetic transmission, and discuss the nature of polygenic traits.
Chromosomesare threadlike strands of DNA molecules that carry genetic information. Genesare DNA segments that serve as the key functional units in hereditarytransmission.
Polygenictraits refer to characteristic that are influenced by more than one set ofgenes. Most psychological characteristics that appear to be affected byheredity seem to involve complex polygenic inheritance. Polygenic traits couldbe influence relatively more easily, which is also a reason for the diversityof some personal traits.
*Compare the special methods usedto investigate the influence of heredity, and discuss how heredity andenvironment interact.
Familystudies are a great way to investigate the influence of heredity. In familystudies, researchers assess hereditary influence by examining blood relativesto see how much they resemble one another on a specific trait. Another way toinvestigate the influence of heredity is twin studies, in which researchersassess hereditary influence by comparing the resemblance of identical twins andfraternal twins with respect to a trait. Identical twins refer to twins emergefrom one zygote, while fraternal twins refer to different zygotes. This methodis useful because the genes in identical twins are 100% overlapped, while infraternal twins are 50% overlapped. Adoption studies assess hereditaryinfluence by examining the resemblance between adopted children and both theirbiological and their adoptive parents.
Therelationship between heredity and environment has been an old topic. By lookingat the importance of genes, we can’t deny the importance of heredity. Bylooking at the environment, we could also understand the powerful influence theenvironment has on us. By conducting various researches, scientists come torealize that heredity and environment jointly influence most aspects of ourbehavior. Their efforts are interactive, which means they play off each other.
3.7 Theevolutionary bases of behavior
*Understand the key insights thatrepresent the essence of Darwin’s theory of evolution.
InDarwin’s theory of evolution, fitness refers to the reproductive success(number of descendants) of an individual organism relative to the averagereproductive success in the population. Variations in reproductive success arewhat really fuels evolutionary change. The principle of natural selectionposits that heritable characteristics that provide a survival or reproductiveadvantage are more likely than alternative characteristics to be passed on tosubsequent generations and thus they come to be “selected” over time.
*Describe subsequent refinement toevolutionary theory, and give some examples of animal behavior that represent adaptations.
An adaptation is aninherited characteristic that increased in a population (through naturalselection) because it helped solve a problem of survival or reproduction duringthe time it emerged. For instance, the eating behavior of rats, which showremarkable caution when they encounter new foods. Rats are versatile animalsthat are found in an enormous range of habitats and can live off quite avariety of foods, but this diet variety can present risks, as they need to bewary of consuming toxic substances. When rats encounter unfamiliar foods, theyconsume only small amounts and won’t eat two new foods together. If theconsumption of a new food is followed by illness, they avoid that food in thefuture. These precautions allow rats to learn what makes them sick, whichreducing the likelihood of consuming a lethal amount of something poisonous.These patterns of eating behavior are highly adaptive solutions to the foodselection problems faced by rats.
3.8Reflecting on the chapter’s themes
*Identify the three unifying themesthat were highlighted in this chapter.
Thethree unifying themes are 1) heredity and environment jointly influencebehavior; 2) behavior is determined by multiple causes; 3)psychology is empirical.
Heredity
and environment influence jointly but there is no gene directly relative to any
of our personality or behavior. It is the psychological makeup that influence
directly by genes and this makeup then influence our behavior. The fact that
behavior is determined by multiple causes is from some abnormal diseases, such
as schizophrenia. It has been demonstrated that this disease is influenced by a
variety of behaviors. The empirical nature of psychology is the core of the
enterprise as almost scientific studies are based on this principle.
3.9Personal application: evaluating the concept of the “two minds in one”
*Describe and evaluate threepopular beliefs regarding the specialization of the cerebral hemisphere.
Thethree popular beliefs are 1) the two hemispheres are specialized to processdifferent types of cognitive tasks; 2) The two hemispheres have different modesof thinking; 3) people vary in their reliance on one hemisphere as opposed tothe other.
Theleft hemisphere is more capable of verbal tasks, while the right is more ofnonverbal ones. This also leads to different processes of perceivinginformation between the two hemispheres. It is believed that the left is moreanalytic, logical, linear, while the right is more synthetic, nonrational,holistic. People have been training their brains since they were born, whichleads to different reliance in using the brain. This is believed to be one ofthe reasons why people are specialized at different work.
3.10Critical thinking application: building better brains: the perils ofextrapolation
*Explain how neuroscience researchhas been over extrapolated to educational issues.
As Greenough’s researchshowed that the brain may remains malleable throughout life. It has been overextrapolated to set up educational programs for the old to maintain theirintellectual potential. This could a result of the pressure of population ageingin some countries, especially developed countries and China, as well as thefear of getting old. Interest has been aroused in creating cognitive trainingprograms for old adults so that the age-related cognitive decline could beslowed down.
The critical thinkingskills to notice over extrapolated conclusion includes understanding the limitsof extrapolation and looking for contradictory evidence.
Conclusions frompsychological studies could be powerful to influence the public knowledge aspsychology comes from everyday life. Sample bias, experimental bias, andprobability of over extrapolated conclusions and other traps in psychologyshould be part of common-sense knowledge. It is kind of frustrating to see thatpsychology gradually become a hot topic but the popular ideas are not alwayscorrect or acceptable.