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PSY100H1 (1,821)
Chapter 3

Chapter 3

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Dan Dolderman

Chapter 3: Biological Foundations What is the genetic basis of psychological science? – 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. – Dominant gene: a gene that is expressed in the offspring whenever it is present – recessive gene: a gene that is expressed only 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 – monozygotic twins: twin siblings who result from one zygote splitting in two and therefore share the same genes (identical twins) – dizygotic twins: twin siblings who result from two separately fertilized eggs (fraternal twins) – heritability: a statistical estimate of the variation, caused by differences in heredity, in a trait within a population. + depends on variation, the measure of the overall difference among a group of people for that particular trait. Neurons are specialized for communication: – neuron: the basic unit of the nervous system; it operates through electrical impulses, which communicate with other neurons through chemical signals. Neurons receive, integrate, and transmit information in the nervous system – sensory neurons: one of the three types of neurons, these afferent neurons detect information from the physical world and pass it along to the brain – motor neurons: one of the three types of neurons, these efferent neurons direct muscles to contract or relax, thereby producing movement – interneurons: one of the three types of neurons, these neurons communicate only with other neurons, typically within a specific brain region. – Dendrites: branch-like extensions of the neuron that detect information from other neurons – cell body: in the neuron, where information from thousands of other neurons is collected and processed – axon: a long narrow outgrowth of a neuron by which information is transmitted to other neurons – terminal buttons: small nodules, at the ends of axons, that release chemical signals from the neuron to the synapse – synapse (synaptic cleft): the site for chemical communication between neurons, which contains extracellular fluid – 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 the segments of myelin sheath, where action potentials are transmitted – resting membrane potential: the electric charge of a neuron when it is not active Action Potentials cause neural communication: – action potential: the neural impulse that passes along the axon and subsequently causes the release of chemicals from the terminal buttons + neuron respond to incoming stimulation by changing electrically and then passing along signals to other neurons. – Excitatory: signals depolarize the cell membrane, increasing the likelihood that the neuron will fire – inhibitory: signals that hyperpolarize the cell, decreasing the likelihood that the neuron will fire – two signals received by dendrites are integrated within the neuron. + if the total amount of excitatory input from the other neuron surpasses the receiving neuron's threshold, an action potential is generated. – When a neuron fires, the sodium gates in cell membrane open, allowing sodium ions to rush into neuron → inside of neuron become more positively charged than the outside. Change of charges is basis of action potential. – Propagation: when neuron fires, the cell membrane's depolarization moves along the axon like a wave. – Through natural restoration (repolarization), the electrical charges returns to its slightly negative resting state. – All-or-none principle: the principle whereby a neuron fires with the same potency each time, although frequency can vary; it either fires or not – it cannot partially fire. Neurotransmitters bind to receptors across the synapse: – neurotransmitter: a chemical substance that carries signals from one neuron to another – presynaptic: sends the signal – postsynaptic: receives the signal – neurons do not touch each other; communicate by sending neurotransmitters from the axon across the synaptic gap to the dendrites of the receiving neuron → neurotransmitters are stored in vesicles → action potentials cause vesicles to fuse to the presynaptic membrane and release their contents into the synapse → neurotransmission is terminated by reuptake, enzyme deactivation, or autoreception → released neurotransmitters bind to the postsynaptic receptors – a neurotransmitter can bind only with its particular type of receptor, much as a key fits only with the right lock – receptors: in neurons, specialized protein molecules, on the postsynaptic membrane, that neurotransmitters bind to after passing across the synaptic cleft. – Reuptake: the process whereby a neurotransmitter is taken back into the presynaptic terminal buttons, thereby stopping its activity. – Three major events that terminate the transmitters' influence in the synaptic cleft are reuptake, enzyme deactivation, and autoreception Neurotransmitters influence mind and behavior – agonist: any drug that enhances the actions of a specific neurotransmitter + can block the reuptake of neurotransmitters – antagonist: any drug that inhibits the action of a specific neurotransmitter + can destroy neurotransmitters in the synapse – acetylcholine (ACh): neurotransmitter responsible for motor control at the junction between nerves and muscles; also involved in mental processes such as learning, memory, sleeping, and dreaming – epinephrine: the neurotransmitter responsible for adrenaline rushes, bursts of energy caused by its release throughout the body + known as adrenaline – norepinephrine: the neurotransmitter involved in states of arousal and awareness – serotonin: a monoamine neurotransmitter important for a wide range of psychological activity, including emotional states, impulse control, and dreaming – dopamine: a monoamine neurotransmitter involved in reward, motivation, and motor control – Parkinson's disease (PD): a neurological disorder that seems to be caused by dopamine depletion, marked by muscular rigidity, tremors, and difficulty initiating voluntary action – GABA(gamma-aminobutyric acid): the primary inhibitory transmitter in the nervous system – glutamate: the primary excitatory transmitter in the nervous system – endorphins: a neurotransmitter involved in natural pain reduction and reward – substance P: a neurotransmitter involved in pain perception + mood states and anxiety Basic brain structures and functions: – central nervous system: the brain and spinal cord + information sent → organizes and evaluates the information – peripheral nervous system: all nerve cells in the body that are not part of the CNS. The PNS includes the somatic and autonomic nervous systems – + transmits a variety of information to the CNS + perform specific behaviors/make bodily adjustments – Broca's area: left frontal region of the brain, crucial for production of language + speech production – brain stem: a section of the bottom of the brain, housing the most basic programs of survival → breathing, swallowing, vomiting, urination, orgasm – cerebellum: a large, convoluted protuberance at the back of the brain stem, essential for coordinated movement and balance – reticular formation: inducing and terminating the different stages of sleep. + sleep and arousal – hypothalamus: a small brain structure that is vital for temperature regulation, emotion, sexual behavior, and motivation + affects many internal organs' functions. – Thalamus: the gateway to the brain; receives almost all incoming sensory information before that information reaches the cortex + during sleep, shuts the gate on incoming sensations while the brain rests – hippocampus: a brain structure important for the formation of certain types of memory + storage of new memories – amygdala: a brain structure that serves a vital role in our learning to associate things with emotional responses and in processing emotional information + fear – basal ganglia: a system of subcortical structures that are important for the initiation of planned movement + receive input from the entire cerebral cortex and project to the motor centres of the brain stem and thalamus The cerebral cortex underlies complex mental activity – cerebral cortex: the outer layer of brain tissue, which forms the convoluted surface of the brain – frontal lobe: thought, planning movement
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