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Synapses and neurotransmitters Biology/Psychology 2606

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  • Synapses and neurotransmittersBiology/Psychology 2606

  • Biochemical ActivityOtto Loewi did a cool experiment in 1921Simulated the vagus nerve is a frogs heartSlowed the heart downWashed heart with solution, collected solutionPoured solution on a second heartIt slowed!!!!

  • Loewi and his frogsCalled the substance vagusstoffAcetylcholineLater stimulated heart rate, similar methodEnded up with a sped up heartEpinephrine

  • The SynapseGap between the axon and the dendriteAbout 20 40 nmNeurotransmitters are released across this gapSometimes, if all of the transmitter isnt absorbed it is taken back up, this is known as reuptake

  • Pools, Vesicles and PoresThree pools of neurotransmittersReady releasableRecycling ReserveFusion poreSNAREFull collapse fusionKiss and run

  • There is lots of variation in synapsesSome are excitatory (Type I) Some are inhibitory (Type II)

  • More about synapsesIs the excitatory vs. inhibitory nature of a synapse due to shape?ProbablyGABA synapses are inhibitory, have less post synaptic thickeningGlutamate synapses have more thickening, more vesiclesThere are 7 types of synapses

  • SEVEN?Yes, SevenDepends on functionWe usually learn about axodendritic ones Easiest to think about them I guess

  • The Seven Steps in NeurotransmissionSynthesisStorageReleaseReceptor interactionInactivationReuptakeDegradation

  • The NeurotransmittersBasically, five conditions must be met before we call something a neurotransmitterPresent in terminalReleased on firingPlacing substance on organ or another neuron emulates firingUptake for inactivationInactivation blocks stimulation

  • The NeurotransmittersAcetylcholine (Ach)MonoaminesCatecholaminesNorepinephrine (NE)Epinephrine (E)Dopamine (DA)IndoleamineSeretonin (5-Ht)OthersHistamine (H)

  • More neurotransmittersAmino AcidsGlutamate (universally excitatory)GABA (universally inhibitory)GlycineProlinePeptidesSubstance P

  • Finally.Morphine like substancesEndorphinsEnkephalinsOther peptidesInsulinProlactinHGHVasopressin

  • ReceptorsTransmitters bind to receptorsSort of like a lock and a keyBinding siteIon channelOne neuron (usually) has only one type of receptorGreat place for drug interaction

  • Electrical SynapsesOnly 2.5 nm apartAllows flow of ions from one neuron to anotherBi directionalUsed when you need very fast reaction, say for defensive beahviour, that sort of thingNo receptor or binding site, but a connexon

  • Synapses, neurotransmitters, learning and memoryThe Hebbian synapseWhen an axon of cell A is near enough to excite cell B and repeatedly or persistenly takes part in firing it, some growth process or metabolic change takes place in one or both cells such that As efficiency as one of the cells firing B, is increased

  • HabituationDecrease in the strength of a response after repeated presentation of a discreet stimulusGetting used to it, sort ofNOT sensory adaptation or simply fatigueStimulus specificOrienting responseStartle response

  • The rulesThompson and Spencer (1966)Gradual with timeWithhold stimulus and response will reoccurSavingsIntensityOverlearningStimulus generalization

  • Pokin aplysisaKendel et alGill withdrawalSeonsory -> motor pretty muchLess transmitter released into synapses!Decrease in Ca currentSimilar results in catsBecause of its generality, habituation is often thought of as the universal learning paradigm

  • LTPLong Term potentiationNMDA (a neuromodulator) basically allows LTP to happenBlock NMDA, block LTPBlock LTP, block learning in say a Morris water mazeBut..Deb Saucier.

  • Barnea and Nottebohm (1994)Chickadees store in the fall and winter, lessen off in the springHP seems to shrink and grow!!

  • In conclusionMuch of the interesting activity in the nervous system takes place at the synapseThis is where the electrical goes chemicalThis is where learning MAY be happeningThere is still much to learnEvery mall in Athens has a store called The Synapse

    SNARE protein SNAP Soluble NSF Attachment Protein) Receptor