Properties of the Synapses

Gaps Between NeuronsFirst deduced by Sherington

Graded PotentialsEither Depolarization (Excitation) or Hyperpolerization (Inhibition) of the Postsynaptic Neuron

Graded depolarization is known as Excitatory Postsynaptic Potential (ESPS) & occurs when Sodium (Na+) ions enter the postsynaptic neuron

SummationSummationTemporal SummationTemporal SummationRepeated stimulation of one Presynaptic Neuron Repeated stimulation of one Presynaptic Neuron occurring within a brief period of time that has a occurring within a brief period of time that has a cumulative effect on the Postsynaptic Neuroncumulative effect on the Postsynaptic Neuron

Spatial SummationSpatial SummationSeveral synaptic inputs originating from separate Several synaptic inputs originating from separate locations exerting a cumulative effect on a locations exerting a cumulative effect on a postsynaptic neuronpostsynaptic neuron

Inhibitory Postsynaptic Inhibitory Postsynaptic Potential (IPSP)Potential (IPSP)When Potassium (KWhen Potassium (K+)+) leaves the cell or chloride leaves the cell or chloride enters the cell after stimulationenters the cell after stimulation

Spontaneous Firing RateSpontaneous Firing RateThe ability to produce Action Potentials without The ability to produce Action Potentials without synaptic inputsynaptic input

Synaptic Synaptic TransmissionTransmission

Events at the SynapseAction Potentials cause Calcium to enter the cell leading to the release of Neurotransmitters

Released Neurotransmitters attach to Receptor sites altering the activity of the Postsynaptic Neuron

Neurotransmitters will separate from their Receptors & are at times converted into Inactive Chemicals

Reuptake occurs in some cells recycling Neurotransmitters

In some cells empty Synaptic Vesicles are returned to the cell body

Types of Types of NeurotransmittersNeurotransmitters

Amino Acids: Acids containing an amine groupPeptides: Chains of amino acidsAcetylcholine: A chemical similar to an amino acidMonoamines: Nonacidic neurotransmitters containing an amine group & formed by a metabolic change in an amino acidPurines: Adenosine & several of its derivativesGasses: Includes nitric oxide & possibly others

Neurotransmitters

Synthesized from Precursors derived from FoodPhenylalanine & Tyrosine precursors for the Catecholimines

Catecholimines: Dopamine, Epinephrine, & Norepinephrine

Choline is the precursor for acetylcholine found in foods containing lecithin

Tryptophan is the precursor for serotonin

Transport of NeurotransmittersCertain Neurotransmitters (e.g. acetylcholine) synthesized in the Presynaptic Terminal

Larger Neurotransmitters synthesized in the cell body & transported down to the axon terminal

Transporting of Neurotransmitters can take hours or days for long axons

Neurotransmitter ReleaseStored in Synaptic Synaptic VesiclesVesiclesDepolarization occurs when Action Potential reaches the Axon TerminalAfter release, there is diffusion across Synaptic CleftBrain uses dozens of Neurotransmitters

Effects of Neurotransmitters

Ionotropic EffectNeurotransmitter attaches to the receptor causing the immediate opening of an Ion Gate

Metabotropic EffectNeurotransmitter attaches to a receptor & initiates a cascade of metabolic processes

NeuromodulatorsMainly peptides, that do not excite or inhibit neurons but alter the effects of a neurotransmitter

Inactivation & Reuptake

InactivationInactivation occurs shortly after binding to Postsynaptic ReceptorsNeurotransmitter activation occurs in different waysAcetylcholinesterase breaks down Acetylcholine after release from the receptorRapid series of Action Potentials can release neurotransmitters faster than a presynaptic cell can synthesize it bringing transmission to a stop

ReuptakeSerotonin & Catecholamines go through reuptake after leaving Postsynaptic ReceptorReuptake occurs through specialized proteins called TransportersSome Serotonin & Catecholamine molecules converted into inactive chemicals by Enzymes

Drugs’ Affects on Drugs’ Affects on SynapsesSynapses

AntagonistAntagonistA drug that blocks the effects of A drug that blocks the effects of NeurotransmittersNeurotransmitters

AgonistAgonistA drug that mimics a NeurotransmitterA drug that mimics a NeurotransmitterDrugs’ influence Synaptic activity:Drugs’ influence Synaptic activity:1. Alters synthesis of Neurotransmitter1. Alters synthesis of Neurotransmitter2. Disrupts the Vesicles2. Disrupts the Vesicles3. Increases the release of Neurotransmitter3. Increases the release of Neurotransmitter4. Decreases Reuptake4. Decreases Reuptake5. Blocks Neurotransmitter breakdown into 5. Blocks Neurotransmitter breakdown into an inactive chemicalan inactive chemical6. Directly stimulates the blocking of Post-6. Directly stimulates the blocking of Post-synaptic Receptorssynaptic Receptors

AffinityAffinityEfficacyEfficacy

Synapses & PersonalityImportant in Almost All BehaviorVariance of Receptor Levels may be a genetic marker of PersonalityWeak correlations found for certain types of behavior & Dopamine ReceptorsD2 Receptor implicated in risky behaviors, D4 Receptor associated with “novelty-seeking personality