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Final Exam Chapter Summaries

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Psychology 1000
Derek Quinlan

Chapter 3 Biological Foundations of Behaviour Neurons Basic building blocks of the nervous system 100 billion at birth, lose 10,000 every day Three main parts: o Cell body or Soma Contains biochemical structures needed to keep the neuron alive Nucleus carries genetic information that determines how the cell develops and functions o Dendrites Branch-like fibres that emerge from the cell body Collect messages from neighbouring neurons and send them to cell body o Axon Extends from cell body, conducting electrical impulses to other neurons, muscles, or glands Branches out to form axon terminals Connect with dendritic branches from numerous neurons Glial cells surround neurons and hold them in place o Also manufacture nutrients, form myelin sheath, absorb toxins and waste o Guide newly divided neurons to place in brain during development Blood-brain barrier prevents substances from entering brain Nerve Conduction Neurons surrounded by salty liquid environment o High concentration of sodium (Na+) o Inside of neuron is more negative, causing it to be more electrically negative o Resting potential across the membrane: -70 mV Action potential (nerve impulse) is a sudden reversal in neurons membrane voltage o Depolarization - changes from 70 mV to +40 mV o Graded potentials changes proportional to the amount of incoming stimulation If potentials arent very strong, the neuron will be partially depolarized, but not enough for action potential If strong enough, graded potential reaches action potential threshold about 55 mV (obeys all-or-none law) o Graded potentials changes membrane potential by acting on tiny protein structures in the cell membrane called ion channels Open channels allow rushing in of Na+, making neuron less negative Creates state of partial depolarization that may reach action potential o When membrane reaches action potential threshold, Na+ rushes in due to attraction to negative force in cell Ion channels close quickly, K+ channels open and K+ leaves cell Restores neuron to resting potential Na+ and K+ flow back to respective positions to restore distribution o Refractory period time period during which the membrane is not excitable and cannot discharge another action potential Occurs immediately after impulse passes Limits rate at which action potentials can be triggered (300 impulses per second in human) o Rate of firing or number of neurons fired help differentiate between strength of stimuli Myelin sheath is a fatty, whitish insulation layer derived from glial cells that covers axons o Thins out at regular intervals, by nodes of Ranvier o Allow for high conduction speeds along axon (still slower than speed of electricity in electrical wire) Synaptic Transmission Otto Loewi discovered that neurons release chemicals to pass over to next neuron Researchers found synaptic cleft between axon terminals of one neuron and dendrite of the next Neurons produce neurotransmitters to carry messages across synapse to excite or inhibit other neurons o Process involves five steps: Synthesis chemical molecules formed inside neuron Storage molecules stored in synaptic vesicles Release Action potential causes vesicle to move to surface of terminal, molecules are released into fluid-filled space Binding molecules cross the space and bind to receptor sites (large protein molecules embedded in the membrane) Deactivation o Binding of neurotransmitters to receptor site causes two possible effects: Excitation depolarizes the postsynaptic cell membrane by stimulating flow of Na+ (excitatory transmitters) Inhibition hyperpolarizes the postsynaptic cell membrane by stimulating ion channels that allow K+ to flow out of the neuron, or negatively charged ions to flow in (changes potential from 70 mV to 72 mV) Makes it more difficult for excitatory transmitters at other receptor site to depolarize the neuron to the threshold o Neurotransmitters continue to function until deactivation: Some deactivated by other chemicals in synaptic space that break them down Reuptake transmitters reabsorbed into presynaptic axon terminal o Examples of neurotransmitters: Acetylcholine (Ach) functions in excitatory and inhibitory systems (related to memory, motor, behavioural inhibition) Norepinephrine (NE) functions in excitatory and inhibitory systems (related to arousal, eating) Dopamine (DA) functions in inhibitory, sometimes excitatory, systems (related to arousal, voluntary movement) Seratonin (5-HT) functions in inhibitory and excitatory systems (related to sleep, thermoregulation) Gamma Aminobutynic Acid (GABA) functions in inhibitory systems (related to motor behaviour) o Drugs function by affecting neurotransmitters Increase or decreases amount of transmitter, stimulates or blocks receptor sites, terminates transmitter function Examples: Cocaine stimulates release of dopamine, prevents reuptake Curare blocks receptor sites for ACh, causes complete paralysis Black widow venom stimulates release of ACh Botulism toxin Blocks release of ACh Nicotine stimulates receptor molecules, duplicating effects of ACh Caffeine blocks adenosine receptor sites o Disinhibition inhibition of inhibitory neurons to bring system back to normal state The Nervous System Three major types of neurons the carry out functions: o Sensory neurons carry input messages from the sense organ to the spinal cord and brain o Motor neurons transmit output impulses from the brain and spinal cord to the muscles and organs o Interneurons link input and output function, perform connective or associative functions with the nervous system Allow connection with mental functions, emotion, and behavioural capabilities Peripheral Nervous System contains all neural structures that lie outside of the brain and spinal cord o Neurons help carry input and output functions to sense and respond to stimuli o Two major division of nervous system: Somatic nervous system consists of sensory neurons that transmit messages from sensory receptors (eyes, ears, etc.) and motor neurons that send messages from the brain and spinal cord to muscles controlling voluntary movements Autonomic nervous system controls glands and smooth (involuntary) muscles (heart, blood vessels, etc.) Concerned with involuntary functions (respiration, circulation, digestion, etc.) Two subdivisions: o Sympathetic nervous system activation or arousal function (causes increased heart rate, dilated pupils during stress) o Parasympathetic nervous system slows down body processes and maintains state of tranquility Homeostatis balanced state achieved by equilibrium among two divisions Central Nervous System contains the brain and spinal cord, which connects most parts of the peripheral nervous system with the brain o Spinal cords neurons are protected by the vertebrate Spinal reflexes allow stimulus responses triggered without involvement of the brain o Brain is comprised of protein, fat, and fluid Various methods for studying brain structure and activity: o Neuropsychological tests measure verbal and non-verbal behaviours that are known to be affected by particular types of brain damage o Destructive and Stimulation techniques controlled damage allows researchers to observe consequences Electrical stimulation can allow for similar observations o Electrical recording electrodes can record brain
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