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Neurotransmitters & Synapses E.4.1 State that some presynaptic neurones excite postsynaptic transmission and others inhibit postsynaptic transmission Communication via Synapses • Synapses are a fundamental part of neural pathways • Regulate decision-making in terms of • Exciting or • Inhibiting the post-synaptic neuron Neurotransmitters are: • Excitatory • they excite the post-synaptic neuron (+ ions move in) • Contributing to depolarization & propagation of the AP • Inhibitory • Hyperpolarize the post-synaptic neuron (+ ions move out) • Prevent the AP Will the post-synaptic neuron respond? • Which NT diffused? • Which receptors do they bind to? • Which ions flow in/out of the post-synaptic neurone? • Whether or not depolarization reaches threshold Excitatory Neurotransmitters • • • • • e.g. Ach, dopamine NT binds Na+ channels open Na+ rushes in Membrane potential depolarizes • AP propagated Inhibitory Neurotransmitters • e.g. - GABA, serotonin • NT binds to receptor • K+ channels open, K+ rushes out • OR Cl- channels open, Cl- rushes in • Membrane potential becomes more negative • Ac AP is prevented from p propagating E.4.2 Explain how decision making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurones at synapses. Decision making in the CNS • • • • • Action potential Calcium ions rush to the end of the axon Neurotransmitter fuse with membrane Neurotransmitters released into synaptic cleft Binds to specific receptors on the postsynaptic neurone Decision making in the CNS • Temporal Summation 1. 2. 3. AP arrive in rapid succession Depolarization in the axon hillock is summative If it reaches threshold before repolarization, the AP is propagated • Spatial Summation 1. 2. 3. 4. 5. AP arrive simultaneously from multiple sources Some NT are excitatory Other NT are inhibitory Summation is the axon hillock is summative If it reaches threshold the AP is propagated E.4.3 Explain how psychoactive drugs affect the brain & personality by either increasing or decreasing postsynaptic transmission. How do psychoactive drugs affect the brain? 2 Main Neurotransmitters Acetylcholine Noradrenaline/Norepinephrine Acetylcholine (Ach) • • • • • • Released by all motor neurones Activate skeletal muscles Works with parasympathetic nervous system Causes relaxation Ach synapses = cholinergic synapses Nicotine stimulates these synapses – Causes calming effect Noradrenaline/Norepinephrine • • • • • Depolarizes the the postsynaptic neurone Works with the sympathetic system Causes “fight or flight” Noradrenalin synapses = adrenergic synapses Cocaine & amphetamines stimulate adrenergic synapses – Increased alertness, energy, and euphoria Comparison of synapses Cholinergic Adrenergic Neurotransmitter Acetylcholine Noradrenaline System Parasympathetic Sympathetic Effect on Mood Calming Increased energy, alertness, euphoria Drugs increasing transmission at synapse Nicotine Cocaine and amphetamines Psychoactive drugs • Increase or decrease the release of NTs • Breakdown re-uptake proteins which are responsible for returned used components of NTs to the pre-synaptic neurone • Block re-uptake proteins (e.g. cocaine) • Mimic or block NTs, binding to the receptors on post-synaptic membranes – Inhibit production of new NTs Let’s do this animation http://www.jellinek.eu/brain/index.html?KeepThis=true&TB_iframe=true&height= 588&width=672 E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs E.4.5 Explain the effects of THC & cocaine in terms of their action at the synapses in the brain. THC & Cocaine affect mood, synapse and behaviour E.4.6 Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion. Causes of Addiction Addiction • A chronic neurological disorder with genetic, psychosocial and environmental characteristics – Characterized by changes in the brain resulting in a compulsive desire to use a drug – Body often develops a tolerance and needs more and more of the drug to produce the same result Reward Centers • Plays a key role in reinforcing behavour that may lead to addiction • Dopamine is the neurotransmitter most prevalent in the reward pathways – Drugs that stimulate the reward pathways generate a feeling of pleasure – High levels of dopamine cause a feeling of euphoria & drugs that affect reward pathways are particularly addictive (THC and cocaine) Genetic Predisposition Genetic Predisposition • Study of twins – Identical twins = 100 % – Fraternal twins = 50 % Male twins – if one twin suffers an addiction, the rate of addiction in the second twin is 50% greater with identical twins than fraternal Genetic Predisposition • Children of addicts are more likely to become addicts themselves. • The effect of genetics could be to produce a different allele of a receptor gene, or to carry modified versions of other genes linked to drug metabolism and reward pathways. Remember: Susceptibility does not mean inevitability! Social Factors Peer Pressure Timing Availability Social Factors Legality/Religion Community Family Social Factors Mental Health Issues Mental Health Depression Abuse Low selfesteem Dopamine Secretion • Dopamine activates the “reward pathway” • Receptors constantly stimulated in drug addiction • Over-stimulation decreases the number of receptors and the remaining receptors become less sensitive to dopamine • More and more of the drug is needed to have the normal sense of well-being Dopamine secretion • Scientists studying knockout mice – Genetically manipulated mice addicted to cocaine • Found glutamate may be as or more important than dopamine – May oversee the learning and memories which lead to cocaine-seeking Check out this synaptic cleft!!!