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Chapter 3

Psych1000 Chapter 3 - AWESOME notes

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Western University
Psychology 1000
Laura Fazakas- De Hoog

Chapter 3 Note: Look at All Textbook Charts and **Figures** Neural Bases of Behaviour Neurons -Neurons: -basic building blocks of nervous system -linked in circuits -vary in size/shape -3 main parts: 1) cell body (soma) contains biochemical structures for neuron survival, nucleus has its genetic info determining function and development 2) dendrites: fibres, receiving units of impulses 3) axon: conducts impulses away from cell body to other neurons, muscles, glands -branches out into axon terminals: connects to numerous neurons’ dendrites to communicate  one neuron can talk with 50000 others -Glial cells: support neuron function by: -surround them, hold them in place -manufacture nutrient chemical neurons need -form myelin sheath -absorb toxins and wastes -long fibres guide new neurons to targeted area of brain -modulate neuron-neuron communication -protect brain from toxins: blood-brain barrier prevents toxins & other from entering brain -brain blood vessels have smaller gaps & covered in special glial cells Electrical Activity of Neurons Neurons: 1) release chemicals to communicate with muscles, glands, neurons 2) generate electrical nerve impulses Nerve activation: 1) At resting potential (-70mV) the neuron has an electrical potential due to high [Na+] ions outside and neg. protein anions inside (some Cl- outside but not a lot, K+ inside but not as much Na+ as outside)  polarized (inside more neg. than outside) a. sodium-potassium pump maintain charges by moving 3Na+ out for every 2K+ coming in b. sodium and potassium channels are closed 2) When stimulus passes all-or-none law, a. all-or-none law: action potential occur at uniform & maximum intensity or not at all b. occurs by passing the action potential threshold of -50mV caused by stimulus making enough Na+ flow into axon to change internal voltage differential of resting potential c. changes in negative resting potential that don’t reach threshold (not enough stimulus): graded potentials  PROPORTIONAL to stimulus, some situations can build up in a neuron to finally fire it off 3) sodium channel open for instant, Na+ flows into axon attracted to –ve charged proteins, reverse electric potential from -70 to +40mV -this reversal is a nerve impulse and hits action potential at +40mV -depolarization: shift from neg. to pos. voltage across membrane (outside more – now) 4) to attempt to restore balance, within instant, sodium channels close, K+ channels open and they flow out by repulsion a. restores negative voltage resting potential b. this neuron is absolute refractory period: not excitable for a certain time -causes rate of 300 impulses per second max for humans 5) restoration of ions, Na+ goes back out, K+ comes back : repolarization a. this neuron still in refractory as it returns to resting potential b. adjacent sodium channels open... process continues along and keeps moving to axon terminals Hodgkin and Huxley: action-potential -mild electrical stimulus to axon, interior voltage differential shifts from -70mV to +40mV -forced axon to generate a nerve impulse, or action potential -found that relies of sodium potassium channels -some anaesthetics stop flow of Na+ ions, meaning no pain impulses sent by neurons Myelin sheath: -fatty, whitish insulation and protective layer derived from glial cells -covers many axons in brain and spinal cord -speeds up nerve impulses to 300km/h by jumping gaps: -nodes of Ranvier: regular intervals of extremely thin or absent myelin -MS: immune system attacks myelin sheath -damaged myelin disrupts delicate timing of impulses, resulting in jerky movement, and paralysis How Neurons Communicate: Synaptic Transmission -at synapses: functional (but not physical) connection between a neurons (don’t actually touch) -synaptic cleft: tiny gap between axon terminal of one neuron and dendrite of next neuron -Otto Loewi: chemical neurotransmission: neurons release chemicals that carry messages to other cells Neurotransmitters -neurons produce neurotransmitters: chemicals that carry messages across synapse to excite or inhibit firing of other neurons...............steps of chemical communication: (therefore impulses carried btwn by chemicals) -synthesis: chemicals formed inside neuron -storage: in chambers, synaptic vesicles within axon terminals -release: when action potential comes down axon, vesicles move to surface of axon terminal and are released into fluid space between presynaptic (sending) neuron and postsynaptic (receiving) neuron -binding: molecules cross space and attach to receptor sites, fitting like lock-and-key -large protein molecules embedded in postsynaptic neuron’s membrane -deactivation by reuptake or breakdown o Binding of neurotransmitters to receptor site causes two possible effects:  Excitation – depolarizes the postsynaptic cell membrane by stimulating flow of Na+ (excitatory transmitters)  Alone (temporal) or combo (spatial) with other activity at excitatory synapses on dendrites or cell body can exceed threshold and cause postsynaptic to fire  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) (inhibitory transmitters)  Makes it more difficult for excitatory transmitters at other receptor site to depolarize the neuron to the threshold, even if excitatory stimuli from many other neurons at one time o Neurotransmitters continue to do their excitatory or inhibitory function until deactivation by:  Some deactivated by other chemicals in synaptic space that break them down  Reuptake – transmitters reabsorbed into presynaptic axon terminal o Most only effect specific receptors with receptors for them, but neuromodulators have widespread influence by modulating (inc. Or dec.) sensitivity of 10000s of neurons to their specific transmitters: related sleep, eating, and stress o Examples of neurotransmitters: (pg. 76 for disorders associated**)  Acetylcholine (Ach) – excitatory (related to memory storage, muscle activity & movement, behavioural inhibition) –lack: Alzheimers too much: muscle contractions, convulsions  Ex. black widow venom has lots of ACHviolent seizures, death  Glutamate (Glutamic Acid)  found in CNS, therefore related to all behaviour basically  Excitatory  Learning & Memory  Too much causes seizures --------------------  Norepinephrine (NE) – functions in excitatory and inhibitory systems (related to arousal, eating)  Neural circuits controlling memory, learning, wakefulness, eating  Lack: depression too much: panic and stress  Dopamine (DA) – inhibitory or excitatory  Parkinsons and depression (lack) or schizophrenia (too much)  Emotional arousal, voluntary movement, learning, motivation, pleasure ------------------------  Seratonin (5-HT) – mostly inhibitory  sleep, mood, eating, sexual behaviour (arousal), pleasure & pain  Lack: depression, eating, sleeping disorders  Endorphins: inhibits transmission of pain impulses, causes feeling of well-being  too much: cant feel pain too little: immune issues and hypersensitivity to pain  Gamma Aminobutynic Acid (GABA)  functions in inhibitory systems (related to motor control and anxiety control)  ex. drugs to treat anxiety often raise GABA, alcohol raises brain sensitivity to it  Found in CNS, therefore related to all behaviours basically  Lack: tremors, loss of motor control, also personality changes o Drugs function by affecting neurotransmitters  Increase (agonist) or decreases (antagonist) action of neurotransmitter:  stimulates or blocks receptor sites  Enhance or reduce neuron ability to synthesize, store or release transmitters  Make difficult to deactivate transmitter, ex. inhibiting uptake (agonist only)  Examples:  Amphetamines: stimulants that boost arousal and mood by increasing dopamine and norepinephrine activity: o 1) cause neurons release more transmitters o 2) inhibit reuptake  Cocaine – increases activity of dopamine and norepinephrine o 1) inhibits reuptake only  Alcohol – agonist and antagonist: o stimulates GABA: depressing neural activity (agonist) o reduces activity of glutamate o inhibits clear thinking, emotional control and motor  Curare – blocks receptor sites for ACh, causes complete paralysis  Black widow venom – stimulates release of ACh  Botulism toxin – Blocks release of Ach  Rohypnol and GHB: date rape drugs increasing GABA action, reduce memory  Nicotine – “duplicating” effects of Ach by fitting in its receptor sites o Agonist for Ach and dopamine neurons, increasing neural excitation  Caffeine – increases neuron and cellular activity o Antagonist for adenosine transmitter: blocks adenosine receptor sites which inhibits release of excitatory transmitters 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, higher thinking, 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 – allows to sense and respond to environment: consists of:  sensory neurons that transmit messages from sensory receptors (eyes, ears, etc.)  motor neurons that send messages from the brain and spinal cord to muscles controlling voluntary movements  axons join to make sensory nerves and motor nerves (tracts)  Autonomic nervous system – regulates internal environment: controls glands and smooth (involuntary) muscles (heart, blood vessels, etc.)  Concerned with involuntary functions (respiration, circulation, digestion, etc.) as well as stress responses, emotional behaviour, motivation  Two subdivisions that do opposite effects on same organ: o Sympathetic nervous system – activation or arousal function (causes increased heart rate, dilated pupils during stress) fight or flight response  acts as one unit, goes crazy doing shit at same time o Parasympathetic nervous system – slows down body processes and maintains state of rest  Specific functions on specific organs at a time  The two subdivisions maintain Homeostasis – balanced state achieved by equilibrium among two divisions, ex. both needed for male sexual function: erection (para causes dilation of blood vessels) and ejaculation (symp)  Central Nervous System – contains the brain and spinal cord, which connects most parts of the peripheral nervous system with the brain o Spinal cord’s neurons are protected by the vertebrate, motor neurons exit front side, sensory enter back  Spinal reflexes allow stimulus responses triggered without involvement of the brain, reduce reaction time o 1.4kg brain is comprised of protein, fat, and fluid and uses 20% body oxygen  Various methods for studying brain structure and activity: o Neuropsychological tests – measure verbal and non
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