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Psychological Science - Third Canadian Edition - Chapter Three Notes.docx

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INTRODUCTION TO PSYCHOLOGY (CHAPTER 3) HUMAN GENOME PROJECT = an international research effort; represents the coordinated work of hundreds of scientists around the world to map the entire structure of human genetic material; the first project was to map out the entire structure of DNA (deoxyribonucleic acid) and to identify the precise order of molecules that make up the genes on each 23 pairs of human chromosomes CHROMOSOMES = structures within the cell body that are made up of genes GENE = the unit of heredity that determines a particular characteristic in an organism; a segment of DNA which is involved in producing protein which carries out a specific task; the environment determines which proteins are produced and when they are produced; understanding how they work enabled medical researchers to cure various ailments by altering gene functions HEREDITY:  The transmission of characteristics from parents to offspring by means of genes  The mechanisms responsible for heredity were discovered by Gregor Mendel when he developed his technique called selective breeding that strictly controlled which plants bred with which other plants  Deduced that there are dominant genes (expressed in the offspring whenever it is present) and recessive genes (expressed when it is matched with a similar gene from the other parent) GENOTYPE = the genetic constitution determined at the moment of conception PHENOTYPE = observable physical characteristics that result from both genetic and environmental influences POLYGENIC EFFECT = when a population displays a range of variability for a certain characteristic such as height or intelligence; influenced by many genes; example: skin colour HOW GENOTYPIC VARIATION IS CREATED BY SEXUAL REPRODUCTION:  Siblings may differ in eye colour, height and personality because each person has a specific combination of genes, determined in part by random cell division before reproduction  In each parent, reproductive cells divide to produce gametes (the egg and sperm)  After sperm and egg combine during fertilization, the joined cell (zygote) contains 23 pairs of chromosomes; half from the mother and half from the father  From any two parents, eight million different combinations of the 23 chromosomes are possible  The outcome is that a unique genotype is created and this accounts for the genetic variation of human species SICKLE-CELL DISEASE = a genetic disorder that alters the bloodstream’s processing of oxygen; leads to pain, organ and bone damage and anemia; recessive HOW GENES AFFECT BEHAVIOUR:  Abilities and psychological traits are influenced by the interaction of genes and the environment  The study of how genes and environment interact to influence psychological activity is known as behavioural genetics BEHAVIOURAL GENETICS METHODS:  Behavioural geneticists use two methods to assess the degree to which traits are inherited o Twin studies compare similarities between different types of twin to determine the genetic basis of specific traits; monozygotic twins (identical twins) result from one fertilized egg dividing into two and therefore each twin has the same chromosomes and genes; dizygotic twins (fraternal) result from two fertilized eggs developed in the womb; o Adoption studies compare the similarities between biological relatives and adoptive relatives; similarities among nonbiological adopted siblings have more to do with environment than with genes HERITABILITY = a statistical estimate of the variation, caused by differences in heredity, in a trait within a population; depends on the variation, the measure of the overall difference among a group of people for that particular trait; refers to populations, not individuals; estimates of heritability are concerned only with the extent that people differ in terms of their genetic makeup within the group HOW SOCIAL AND ENVIRONMENTAL CONTEXTS INFLUENCE GENETIC EXPRESSION:  Because genes and social contexts interact, separating their independent effects can be very difficult HOW GENETIC EXPRESSION CAN BE MODIFIED:  Researchers can employ various gene manipulation techniques to enhance or reduce particular genes’ expression or even to insert genes from one animal species into embryos of another and then compare the genetically modified animals with unmodified ones to test theories about the affected gene’s functions  Such techniques have increased the understanding of how gene expression influences thought, feeling and behaviour  Changing even a single gene can dramatically change behaviour; various gene manipulations have created anxious mice, hyperactive mice, mice that cannot learn, etc. NEURONS = the basic unit of the nervous system and are cells that specialize in communication; they operate through electrical impulses and communicate with other neurons through chemical signals; they receive, integrate and transmit information in the nervous system TYPES OF NEURONS: 1. Sensory = detect information from the physical world and pass that information along to the brain usually via the spinal cord; often called afferent neurons because they carry information to the brain; consists of somatosensory neurons that provide information from muscles and is the general term for sensations experienced from within the body 2. Motor = direct muscles to contract or relax, thereby producing movement; most are efferent and transmit signals from the brain to the muscles throughout the body 3. Interneurons = communicate within local or short-distance circuits; integrate neural activity within a single are rather than transmitting information to other brain structures or to the body organs NEURON STRUCTURE:  The dendrites are branchlike extensions of the neuron that detect information from other neurons  In the cell body receives the information, where it is processed and integrated  Once the incoming information from many other neurons has been integrated in the cell body, electrical impulses are transmitted along a long narrow outgrowth known as the axon  Terminal buttons, small nodules at the axons’ ends, receive the electrical impulses and release chemical signals from the neuron to an area called the synapse, or synaptic cleft, the site for chemical communication between neurons.  Neurons do not touch each other; they communicate by sending chemicals into tiny gaps between the axon of the “sending” neuron and the dendrites of the “receiving” neuron.  Chemicals leave one neuron, cross the synapse, and pass signals along to other neurons’ dendrites.  The neuron’s membrane serves as its boundary and regulates the concentration of electrically charged molecules  Myelin sheath = a fatty material made up of glial cells that insulates the axon and allows for the rapid movement of electrical impulses along the axon  Nodes of Ranvier = small gaps of exposed axon between segments of myelin sheath where action potentials are transmitted  The resting membrane potential is negatively charged because the ratio of negative and positive ions is greater inside the neuron than outside of it; changing this charge inside and outside the neuron is called polarization which creates the electrical energy necessary to power the firing of the neuron THE ROLES OF SODIUM AND POTASSIUM IONS:  Types of ions: sodium and potassium  Ions pass through the cell membrane at ion channels located at the nodes of Ranvier and each channel matches a specific type of ion; the flow is controlled by a gating mechanism  Because of selective permeability of the cell membrane, more potassium is inside the neuron than sodium ACTION POTENTIAL = the electrical signal that passes along the axon and causes the release of chemicals that transmit signals to other neurons STEPS OF ACTION POTENTIAL: 1. A neuron receives chemical signals from nearby neurons through its dendrites, and these signals tell the neuron whether to fire; two types of signals: excitatory (depolarize the cell membrane, increasing the
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