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Neurons, Neurotransmitters, and Systems

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Neurons, Neurotransmitters, and Systems. Structure of a Neuron. The Withdrawal Reflex. The Neuron in Action. - PowerPoint PPT Presentation

Text of Neurons, Neurotransmitters, and Systems

  • Neurons, Neurotransmitters, and Systems

  • Structure of a Neuron

  • The Withdrawal Reflex

  • The Neuron in ActionResting Potential: an electrical charge of 70 mV across the cell membrane (-inside, + outside) caused by the sodium-potassium pump (pumps 3 Na+ out for every 2 K+ in) and the impermeability of the cell membrane to Na+Graded Potential: small changes in resting potential caused by other neurons; hyperpolerization (inhibitory) vs. depolarization (excitatory)Threshold: the point at which a neuron has been depolarized enough to trigger an action potentialAction Potential: an electrical impulse that surges along an axon; caused by an influx of Na+ ions into the neuron; causes communication with any neuron it contacts

  • Some interesting facts and ideas100 to 200 billion neurons in the brain aloneA neuron with a moderate amount of dendrites receives between 1000 and 10000 contactsSome neurons in the cerebellum receive 150,000 contacts!A mental code (i.e., mental representation) is a pattern of neurons firing in (sometimes) several different locations in the brain simultaneouslyOur brain has trillions of connections which can be used to code trillions of mental representations

  • Laws and implications of action potentialsAll or none law: neurons either fire an action potential or they do not; there are no halfway responsesAction potentials do not vary in intensity, either within the same neuron at different times or across different neuronsInformation is conveyed by the number and frequency of action potentialsThe information conveyed by an action potential depends on the pathway it is a part of. The image of a bee and the sound of bee are both conveyed by a chain of action potentials, but in different parts of the brain

  • Terminating synaptic transmissionIf the neurotransmitters were allowed to stay in the synaptic gap, they would continue to bind with receptors and thus prevent new signals from being communicated.So, the influence of the neurotransmitters must be temporarily terminated; that is, the synapse needs to reset itself.Three termination processesReuptakeEnzyme deactivationAutoreceptors: a homeostatic device

  • NeurotransmittersThe inhibitory or excitatory effects of neurotransmitters are a function of the receptor with which they bind and not a function of the neurotransmitter itself.Different areas of the nervous system rely on different neurotransmitters for interneuronal communicationAcetylcholineFirst neurotransmitter discoveredLinks motor neurons & musclesCurare blocks the release of AChBotulism also blocks the release of AChBlack widow bite floods the synapse with AchImportant for learningPeople with Alzheimers have low levels of ACh

  • Neurotransmitters II: MonoaminesDopamineDrugs ranging from marijuana to heroin increase the amount of dopamine in neural pathways responsible for experiencing pleasureHigh levels of dopamine in some parts of the brain have been linked to schizophreniaDegeneration of dopamine-producing neurons in the substantia nigra produces Parkinsons diseaseEncephalitis lethargica and L-dopaSerotoninLow serotonin levels in severe depression; may be responsible for sleep disturbances in depressionLow serotonin levels associated with increased aggressionNorepinephrineIncreases emotional arousal (fear and anxiety) and alertness

  • Neurotransmitters IIIAmino acidsGamma amino butyric acid (GABA)Main inhibitory neurotransmitter in the brainLowers arousal and regulates anxietyAlcohol does the same thingGlutamateMain excitatory neurotransmitter in the brainPeptides: modify effects of neurotransmittersEndorphinsEndogenous [produced within the body] morphine; opiates mimic the actions of endorphinsElevates mood and reduces pain

  • Agonistic and antagonist drug effects

    Behavioral Neuroscience*2001 Prentice Hall*Prepared by Terrence M. Barnhardt, Ph.D., & Michael J. Renner, Ph.D. Some of these slides 2001 Prentice Hall Psychology Publishing.

    Behavioral Neuroscience*2001 Prentice Hall*nodes of RanvierTerminal buttons or synaptic nobsDestruction of the myelin sheath results in the disease multiple sclerosis.The myelin sheath improves (speeds up) conduction by a factor of 12 (100 ms per 1 m vs. 8 ms per 1 m)

    Figure 2.6 from:Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall.

    Behavioral Neuroscience*2001 Prentice Hall*Three different types of neurons; sensory = afferent, motor = efferent, and interneuron

    Figure 2.5B from:Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall.Behavioral Neuroscience*2001 Prentice Hall*There are a number of other important chemical dynamics at work here; diffusion, concentration gradient, osmosis, hydrostatic pressure, dynamic equilibrium, electrostatic pressureBehavioral Neuroscience*2001 Prentice Hall*Takes 2 ms.Behavioral Neuroscience*2001 Prentice Hall*Synaptic gap is also known as the synaptic cleft

    Figure 2.7 from:Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall.Source:Behavioral Neuroscience*2001 Prentice Hall*Behavioral Neuroscience*2001 Prentice Hall*Behavioral Neuroscience*2001 Prentice Hall*Reuptake: neurotransmitters are taken back into the presynaptic terminal buttonsEnzyme deactivation: Enzymes destroy excess neurotransmitters in the cleftAutoreception: Neurotransmitters bind with receptor sites on the presynaptic neuron and, when an excess has been detected, these sites signal the neuron to stop producing the neurotransmitterBehavioral Neuroscience*2001 Prentice Hall*Involved in complex mental processes such as memory, learning, sleep, and dreamingBotulism, a form of food poisoning, inhibits ACh release and can lead to trouble with breathing and even deathBotulism, in very weak doses, used in cosmetic surgery to reduce wrinklesNicotine (the addictive drug found in tobacco leaves) excites ACh receptors; helps smokers, hurts nonsmokers

    The actions of neurotransmitters can be excitatory or inhibitory

    Parkinsons disease symptoms include rigidity, tremors (often worse on 1 side), slowness of movement, poor balance, walking problems such as shuffling gait and no arm swing

    75 known neurotransmitters; 300 estimated; one of these is nitric oxide (NO), which is normally a gas; of course, its dissolved in water in the body; it takes a large quantity of energy to synthesize in the laboratory (like a lightning bolt) and, in large quantities its poisonous; not nitrous oxide (N2O) or laughing gasBehavioral Neuroscience*2001 Prentice Hall*Encephalitis = inflammation in the brain

    Epidemic broke out in 1917, lasted 10 years, and 5 million people contracted it; symptoms during acute phase were extreme states of arousal; delayed onset symptoms began 5 to 10 years after acute phase; the worst was brain deterioration that left them in a sleep-like state for almost 40 years aware, but stuporous, unable to perform any voluntary movements, to speak, have emotions, etc.; the movie Awakenings was based on an autobiography of Oliver Sacks, who originated the L-dopa treatment; L-dopa causes nausea, vomiting, hallucinations, and other side effects; Awakenings with Robert DeNiro and Robin Williams

    LSD (lysergic acid diethylamide): at low doses, LSD is a serotonin agonist; that is, it increases serotonins inhibitory effects; however, at high doses it is a serotonin antagonist; that is, it decreases serotonins inhibitory effects by binding with what are normally serotonin receptor sites

    MAO (monoamine oxidase) is an enzyme that interrupts the activity of serotonin; thus, one form of antidepressant is the MAO inhibitor, because it serves to increase the activity of serotonin

    Adrenalin = epinephrine; noradrenaline = norepinephrine

    Behavioral Neuroscience*2001 Prentice Hall*Two classes of agents show cross-tolerance, target GABA, and together can cause coma, even death(1) sedative-hypnotic, like alcohol and barbituates(2) antianxiety, like benzodiazepines (e.g., valium) with alcohol and opiates

    MSG (monosodium glutamate) in Chinese food causes some people to react with tingling and numbing

    Behavioral Neuroscience*2001 Prentice Hall*