Synapses and Synapses and neurotransmittersneurotransmitters

Psychology 2606Psychology 2606

Biochemical ActivityBiochemical Activity

Otto Loewi did a cool experiment in 1921Otto Loewi did a cool experiment in 1921Simulated the vagus nerve is a frog’s heartSimulated the vagus nerve is a frog’s heartSlowed the heart downSlowed the heart downWashed heart with solution, collected Washed heart with solution, collected

solutionsolutionPoured solution on a second heartPoured solution on a second heart It slowed!!!!It slowed!!!!

Loewi and his frogsLoewi and his frogs

Called the substance vagusstoffCalled the substance vagusstoffAcetylcholineAcetylcholineLater stimulated heart rate, similar methodLater stimulated heart rate, similar methodEnded up with a sped up heartEnded up with a sped up heartEpinephrineEpinephrine

The SynapseThe Synapse

Gap between the axon and the dendriteGap between the axon and the dendriteNeurotransmitters are released across this Neurotransmitters are released across this

gapgapSometimes, if all of the transmitter isn’t Sometimes, if all of the transmitter isn’t

absorbed it is taken back up, this is known absorbed it is taken back up, this is known as reuptakeas reuptake

There is lots of variation in synapsesThere is lots of variation in synapses Some are excitatory (Type I) Some are excitatory (Type I) Some are inhibitory (Type II)Some are inhibitory (Type II)

More about synapsesMore about synapses

Is the excitatory vs. inhibitory nature of a Is the excitatory vs. inhibitory nature of a synapse due to shape?synapse due to shape?

ProbablyProbablyGABA synapses are inhibitory, have less GABA synapses are inhibitory, have less

post synaptic thickeningpost synaptic thickeningGlutamate synapses have more Glutamate synapses have more

thickening, more vesiclesthickening, more vesiclesThere are 7 types of synapsesThere are 7 types of synapses

SEVEN?SEVEN?

Yes, SevenYes, Seven Depends on functionDepends on function We usually learn We usually learn

about axodendritic about axodendritic ones ones

Easiest to think about Easiest to think about them I guessthem I guess

The Seven Steps in The Seven Steps in NeurotransmissionNeurotransmission

SynthesisSynthesisStorageStorageReleaseReleaseReceptor interactionReceptor interaction InactivationInactivationReuptakeReuptakeDegradationDegradation

The NeurotransmittersThe Neurotransmitters

Basically, five conditions must be met Basically, five conditions must be met before we call something a before we call something a neurotransmitterneurotransmitterPresent in terminalPresent in terminalReleased on firingReleased on firingPlacing substance or organ emulates firingPlacing substance or organ emulates firingUptake for inactivationUptake for inactivation Inactivation blocks stimulationInactivation blocks stimulation

The NeurotransmittersThe Neurotransmitters

Acetylcholine (Ach)Acetylcholine (Ach)MonoaminesMonoamines

CatecholaminesCatecholaminesNorepinephrine (NE)Norepinephrine (NE)Epinephrine (E)Epinephrine (E)Dopamine (DA)Dopamine (DA)

IndoleamineIndoleamineSeretonin (5-Ht)Seretonin (5-Ht)

OthersOthersHistamine (H)Histamine (H)

More neurotransmittersMore neurotransmitters

Amino AcidsAmino AcidsGlutamate (universally excitatory)Glutamate (universally excitatory)GABA (universally inhibitory)GABA (universally inhibitory)GlycineGlycineProlineProline

PeptidesPeptidesSubstance PSubstance P

Finally….Finally….

Morphine like substancesMorphine like substancesEndorphinsEndorphinsEnkephalinsEnkephalins

Other peptidesOther peptides InsulinInsulinProlactinProlactinHGHHGHVasopressinVasopressin

ReceptorsReceptors

Transmitters bind to receptorsTransmitters bind to receptorsSort of like a lock and a keySort of like a lock and a keyBinding siteBinding site Ion channelIon channelOne neuron (usually) has only one type of One neuron (usually) has only one type of

receptorreceptorGreat place for drug interactionGreat place for drug interaction

Synapses, neurotransmitters, Synapses, neurotransmitters, learning and memorylearning and memory

The Hebbian synapseThe Hebbian synapseWhen an axon of cell A is near enough to When an axon of cell A is near enough to

excite cell B and repeatedly or persistenly excite cell B and repeatedly or persistenly takes part in firing it, some growth process takes part in firing it, some growth process or metabolic change takes place in one or or metabolic change takes place in one or both cells such that A’s efficiency as one both cells such that A’s efficiency as one of the cells firing B, is increasedof the cells firing B, is increased

HabituationHabituation

Decrease in the strength of a response Decrease in the strength of a response after repeated presentation of a discreet after repeated presentation of a discreet stimulusstimulus

Getting used to it, sort ofGetting used to it, sort ofNOT sensory adaptation or simply fatigueNOT sensory adaptation or simply fatigueStimulus specificStimulus specificOrienting responseOrienting responseStartle responseStartle response

The rulesThe rules

Thompson and Spencer (1966)Thompson and Spencer (1966)Gradual with timeGradual with timeWithhold stimulus and response will Withhold stimulus and response will

reoccurreoccurSavingsSavings IntensityIntensityOverlearningOverlearningStimulus generalizationStimulus generalization

Pokin’ aplysisaPokin’ aplysisa

Kendel et alKendel et al Gill withdrawalGill withdrawal Seonsory -> motor pretty muchSeonsory -> motor pretty much Less transmitter released into synapses!Less transmitter released into synapses! Decrease in Ca currentDecrease in Ca current Similar results in catsSimilar results in cats Because of its generality, habituation is often Because of its generality, habituation is often

thought of as the universal learning paradigmthought of as the universal learning paradigm

LTPLTP

Long Term potentiationLong Term potentiationNMDA (a neuromodulator) basically allows NMDA (a neuromodulator) basically allows

LTP to happenLTP to happenBlock NMDA, block LTPBlock NMDA, block LTPBlock LTP, block learning in say a Morris Block LTP, block learning in say a Morris

water mazewater mazeBut…..But…..

Deb Saucier….Deb Saucier….

Barnea and Nottebohm (1994)Barnea and Nottebohm (1994)

Chickadees store in Chickadees store in the fall and winter, the fall and winter, lessen off in the lessen off in the springspring

HP seems to shrink HP seems to shrink and grow!!and grow!!

In conclusionIn conclusion

Much of the interesting activity in the Much of the interesting activity in the nervous system takes place at the nervous system takes place at the synapsesynapse

This is where the electrical goes chemicalThis is where the electrical goes chemicalThis is where learning MAY be happeningThis is where learning MAY be happeningThere is still much to learnThere is still much to learnEvery mall in Athens has a store called Every mall in Athens has a store called

‘The Synapse’‘The Synapse’

Other neural learning stuffOther neural learning stuff