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Neurotransmitters and synapses

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Neurotransmitters and synapses. Option E.4. Assessment Statements. E.4.1 State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission. - PowerPoint PPT Presentation

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Neurotransmitters and synapsesOption E.41Assessment StatementsE.4.1 State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission.E.4.2 Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses.E.4.3 Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain.E.4.6 Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion.

Synaptic transmissionNeurons communicate with each other chemically across a space called a synapseOne side of the synapse is the presynaptic membrane of the sending neuron and on the other side of the synapse is the postsynaptic membrane of the receiving neuronMolecule which moves across the space (synaptic cleft) between the two membranes is called a neurotransmitterSpecific neurotransmitter is received by a specific receptor

Excitation and InhibitionSome neurotransmitters are excitatory and stimulate the next neuron to forward the messageDo this by increasing the permeability of the postsynaptic membrane to positive ions, making it easier for positive ions to move inSome neurotransmitters are inhibitory and cause the positive ions to move out of the postsynaptic cellPositive ions move back in to the synaptic cleft chemically depressing the postsynaptic cell and makes it much harder to exciteDecision making in the CNSImpulse which moves down the presynaptic neuron is called the action potentialAs action potential reaches axon bulb, calcium ions rush into the end of the neuronVesicles containing neurotransmitters fuse with the presynaptic membraneNeurotransmitter released into the synaptic cleftNeurotransmitter binds to specific receptors on the postsynaptic membraneReceptors let ions enter or leave when the neurotransmitter binds to them

Excitatory neurotransmittersOne example: acetylcholineGenerates action potentialIncreases permeability of the postsynaptic membrane to positive ionsCauses positive sodium ions to diffuse into the postsynaptic neuronLocalized depolarization occursInside of neuron develops a net positive charge compared to the outsideDepolarization continues as sodium ions diffuse to the next area of the neuronImpulse is carried along the nerveIf threshold is not met, the neuron does not carry the impulse to the next neuron

Inhibitory neurotransmittersExample: GABAInhibit action potentialsCauses hyperpolarization of the neuronInside of the neuron becomes more negative making it difficult for an action potential to be generatedGABA binds to specific receptorCauses negatively charged chloride ions to move across the postsynaptic membrane into the postsynaptic cell OR it can cause positively charged K+ ions to move out of the postsynaptic neuronMovement of Cl- into the neuron or K+ out causes hyperpolarization

Putting it togetherA neuron is always on the receiving end of many excitatory and inhibitory stimuliNeuron sums up the signalsIf the sum of the signals is inhibitory then the axon does not fireIf the sum of the signals is excitatory, the axon firesSummation of the messages is the way that decisions are made by the CNSCholinergic synapsesAcetylcholine is released by all motor neurons and activates skeletal muscleIf it remained in the synapse, the postsynaptic membrane would go on firing indefinitelyAcetylcholinesterase breaks it downAcetylcholine is involved in the parasympathetic nervous systemCauses relaxation rather than flightNicotine stimulates transmission in cholinergic synapses which is why it has a calming effect on the body and personalityPeople addicted to nicotine become very agitated if they cannot have a cigaretteAdrenergic synapsesNoradrenaline depolarizes the postsynaptic neuronNoradrenaline is involved in the sympathetic sysemIt causes a fight or flight reactionCocaine and amphetamines both cause increased alertness, energy and euphoriaCholinergicAdrenergicNeurotransmitterAcetylcholine (Ach)NoradrenalineSystemParasympatheticSympatheticEffect on moodCalmingIncreased energy, alertness, and euphoriaDrugs increasing transmission at synapseNicotineCocaine and amphetaminesEffect of drugs on the brainCan alter your mood or your emotional stateExcitatory drugs (nicotine, coaaine, amphetamine) increase nerve transmissionInhibitory drugs (benzodiazepines, alcohol, and THC) decrease the likelihood of nerve transmissionDrugs can change synaptic transmission in the following ways:Block a receptor for a neurotransmitter (structure similar to the transmitter)Block release of neurotransmitter from the presynaptic membraneEnhance neurotransmission by mimicking a neurotransmitterBlock removal of neurotransmitter from the synapse and prolong the effect of the neurotransmitterExcitatory drugs and how they actNicotine mimics acetylcholine (Ach)Acts on the cholinergic synapses of the body and the brain to cause a calming effectAfter Ach is received by the receptors, it is broken down by acetylcholinesterase but it cannot break down nicotineThis excites the postsynaptic neuron and it begins to fire, releasing a molecule called dopamineDopamine gives you a feeling of pleasureCocaine stimulates transmission at adrenergic synapses and causes alertness and euphoriaCauses dopamine releaseCocaine blocks removal of dopamine from the synapse so that it builds upLeads to overstimulation of the postsynaptic neuronLeads to euphoria

Both of these drugs causes addictionAmphetamine stimulates transmission at adrenergic synapses and gives increased energy and alertnessAmphetamine acts by passing directly into the nerve cells which carry dopamine and noradrenalineIt moves directly into the vesicles of the presynaptic neuron and causes their release into the synaptic cleftNormally these would be broken down, but amphetamines interfere with breakdownHigh concentrations of dopamine cause euphoria and high concentrations of noradrenaline may be responsible for the alertness and high energy effectInhibitory drugs and how they actBenzodiaizepine reduces anxietyCan be used against epileptic seizuresModulates the activity of GABA which is the main inhibitory neurotransmitterWhen GABA binds to the postsynaptic membrane, it causes Cl-to enter the neuronCauses hyperpolarization and resists firingB increases the binding of GABA to the receptor and therefore greater hyperpolarizationAlcohol acts similarly to B in that it increases the binding of GABA to the postsynaptic membraneDecreases activity of glutamate, an excitatory neurotransmitterAlcohol helps to increase the release of dopamine by a process which is not well understoodAppears to stop the activity of the enzyme which breaks down dopamine in the synaptic cleftTetrahydrocannabinol (THC) is the main pschoactive chemical in marijuanaTHC mimics the neurotransmitter, anandamideTHC binds to the same receptor and cause the postsynaptic neuron to be hyperpolarizedAnandamide may play a role in memory functions, such as eliminating information from our memory that is not neededMarijuana disrupts short-term memory in humansTHC effectsFeelings of relaxation, lightheadedness, hazinessDecrease in learning, coordination, problem-solving, and short-term memory Stays in synapse longer than anandamideHigh concentrations of receptors found in hippocampus (short-term memory); cerebellum (coordination)Cocaine effectsEuphoria, talkativeness, increase in mental alertnessTemporary decrease in the need for food and sleepLarge amts. Cause erratic and violent behaviorSustains level of dopamine in the synapseCauses of addictionBody develops a tolerance and needs more of the drug to produce the same resultChemical dependency is caused by drug rewiring the brain and becoming an essential biochemical in the bodyRole of abused drugs is to stimulate the reward pathway located in the brain

Withdrawal symptomsAnxiety, depression, cravingSeizures, severe shakingContinued addictionLung damageRisk of contracting HIV, hepatitis B and CKidney diseaseGenetic predispositionStudies in male twins find that when one twin suffers an addiction to alcohol or drugs, the rate of addiction in the second twin is 50% greater among identical twins than among fraternal twinsOther experiments indicate that a genetically determined deficiency of dopamine receptors predisposes certain people to addictionPersons who become addicted to drugs that increase dopamine levels do so to compensate for that deficiencySocial factors of addictionFamily addiction, family parenting skills, mental health problems of family or childOften related to peer group; users teach new users what effects to expect and what altered state is desirableAlcohol at social gatherings fosters the paradigm that it must be available to have a partyAlcohol very rare in Saudi Arabia since it is prohibited

Dopamine secretionNeurotransmitter which activates the reward pathway and gives us a sense of pleasure or satisfactionDuring cocaine use, dopamine builds up in the synapseOver-stimulation decreases the number of receptors and the remaining receptors become less sensitive to dopamine (desensitization or tolerance)

With tolerance, exposure to the drug causes less response that it previously causedMore and more of the drug is needed to have even the normal sense of well-beingType of neuroadaptive change

Knockout miceGenetically manipulated mice addicted to cocaineStudies show that glutamate may oversee the learning and memories which lead to cocaine-seekingMouse party

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