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Chapter 3

Textbook notes for chapter 3 of Psychological Science

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University of Toronto St. George
Ashley Waggoner Denton

Genetic basis of psychology: - The environment we are raised in affects how certain genes are expressed (turned on or off) (82) - Within every cell there is a genome (blueprint) to make the entire organism, and whether a cell becomes thing x or thing y is determined by which genes are turned on or off in that cell (83) - Within each cell are chromosomes, which are structures within the cell body made up of genes (83) - The sequence of molecules along DNAstrands found in genes is an exact instruction to manufacture a specific protein (83) - Proteins are the basic chemicals that make up the structure of cells and direct their activities (83) - Genes are segments of DNAinvolved in producing a protein which carries out a specific task (83) - The way cells develop is influenced by their environment, since each cell contains the same DNA(83) - Gregor Mendel developed selective breeding that strictly controls which plants breed with other plants, ex. breeding purple flowers with white ones to see which color flowers the plants would produce, which resulted in a first generation that was all white or all purple and a second generation that was 75% one colour and 25% the other (85) - Dominant genes are expressed in offspring whenever they are present, while recessive genes are expressed only when matched with a similar gene from the other parent (85) - Genotype = genetic constitution determined at the moment of conception (86) - Phenotype = observable physical characteristics that result from both genetic and environmental influences, i.e. which genes are expressed (86) - Many human characteristics like skin colour and intelligence are the result of many genes instead of just one gene and are polygenic (86) - Each person has a specific combination of genes, determined in part by random cell division before reproduction (86) - Most cells contain 23 pairs of chromosomes, including the x and y chromosomes (86) - For reproduction, the cells divide to form gametes that contain half of every chromosome pair (86) - After the sperm and egg combine, the zygote contains 23 pairs of chromosomes, half of each pair from the father and the other half from the mother (86) - From any two parents, eight million different combinations of the 23 chromosomes is possible, which accounts for the genetic variation of human beings (86) - The zygote goes through cell division where the chromosomes duplicate and then the cell divides into two new cells with an identical chromosome structure (86) - Errors sometimes occur during cell division and lead to mutations (87) - Monozygotic (identical) twins result from one zygote splitting in two (89) - Dizygotic (fraternal) twins result from two separately fertilized eggs (89) - Heritability = a statistical estimate of the variation, caused by differences in heredity, in a trait within a population, ex. height is 60% dependent on heredity (91) - Scientists can knock out certain genes in mice and other animals to determine which function this gene serves (93) The nervous system: - Neurons = cells that specialize in communication (96) - Neurons operate through electrical impulses and communicate through chemical signals (96) - They receive, integrate, and transmit information in the nervous system (96) - Afferent neurons = neurons that carry information to the brain (96) - Efferent neurons = neurons that transmit signals from the brain to the muscles (96) - Sensory neurons = afferent neurons that detect information and pass that information along to the brain (96) - Motor neurons = efferent neurons that direct muscles to contract or relax, producing movement (96) - Interneurons communicate only with other neurons within a specific brain region (96) - Dendrites = branchlike extensions of the neuron that detect information from other neurons (97) - Cell body = where information from other neurons is collected and processed (97) - Axon = a long, narrow outgrowth of a neuron by which information is transmitted to other neurons (97) - Terminal buttons = small nodules at the ends of axons that release chemical signals from the neuron to the synapse (97) - Synapse/synaptic cleft = the site for chemical communication between neurons, which contains extracellular fluid (97) - Neurons don’t touch; they communicate by sending chemicals into tiny gaps between the axon of the sending neuron and the dendrites of the receiving neuron (97) - The neuron’s membrane is its boundary and regulates the concentration of electrical activity in the neuron (97) - Electrical signals travel quickly down the axon because of the fatty myelin sheath that encases and insulates it (98) - The myelin sheath grows along an axon in short segments (98) - Between these segments are small gaps of exposed axon called nodes of Ranvier (98) - At these gaps are ion channel, which allow ions to pass in and out of the cell when the neuron transmits signals down the axon (98) - Resting membrane potential = electrical charge of a neuron when it isn’t active (98) - The resting membrance potential is negatively charged because there are more negative than positive neurons inside the neuron (98) - Since the inside is more negatively charged than the outside of the neuron, there is enough electrical energy to power the firing of the neuron (98) - Ions pass through each cell membrane at ion channels, which are specialized pores located at the nodes of Ranvier (99) - Each channel matches a specific type of ion, i.e. sodium or potassium, and the flow of ions is controlled by a gating mechanism (99) - The membrane allows some types of ions to pass more easily than others, and thus more potassium is inside the neuron than sodium, which allows polarization (differential electric charge creating electrical energy) to happen (99) - Neural communication depends on action potential, which is the neural impulse that passes along the axon and causes the release of chemicals from the terminal buttons (99) - This allows neurons to transmit signals to other neurons (99) - Chemical signals are either excitatory or inhibitory (99) - Excitatory signals depolorize the cell membrane so it is more likely to fire, while inhibitory signals hyperpolarize the cell so it is less likely to fire (99) - If the total amount of excitatory input from other neurons surpasses the receiving neuron’s threshold, and action potential is generated (99) - When a neuron fires, sodium rushes into the neuron which causes the inside of the neuron to become more positively charged than the outside (99) - Potassium channels then open to allow potassium ions to rush out (99) - This change from a negative charge to a positive one inside the neuron is the basis of action potential (99) - The electrical charge inside the cell thus starts out as slightly negative, then becomes positive as it fires and allows more positive ions inside the cell, then goes back to its slightly negative resting state (99) - When a neuron fires, the cell membrane’s depolarization moves along the axon like a wave (99) - Sodium ions rush through their ion channels, causing adjacent sodium channels to open, so sodium ion channels open successively, moving down the axon away from the cell body to the terminal buttons (99) - Deterioration of the myelin sheath leads to multiple sclerosis as neural impulses are slowed (100) - Neurons are generally barraged by thousands of excitatory and inhibitory signals and its firing is
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