NEURAL TRANSMISSIONNEURAL TRANSMISSION

NeuronsNeurons

Electrical and Chemical TransmissionElectrical and Chemical Transmission

Neurons Neurons

NeuronsNeurons

Glial CellsGlial Cells

AstrocytesAstrocytes– Contact blood vessels and neuronsContact blood vessels and neurons– transport chemicals from blood to neuronstransport chemicals from blood to neurons

OligodendrocytesOligodendrocytes– Myelinate CNS axonsMyelinate CNS axons

Schwann cellsSchwann cells– Myelinate PNS axonsMyelinate PNS axons– Guide regeneration after damageGuide regeneration after damage

Radial glia Radial glia – Guide neural migration during developmentGuide neural migration during development

CELL MEMBRANESCELL MEMBRANES

Membrane StructureMembrane Structure– Semipermeable lipid Semipermeable lipid

bilayerbilayer– ProteinsProteins

Ion channelsIon channels

Transport pumpsTransport pumps

ReceptorsReceptors

MEMBRANE POTENTIALMEMBRANE POTENTIAL

MEMBRANE POTENTIALMEMBRANE POTENTIAL

Electrochemical Gradient Electrochemical Gradient – Electrostatic ForcesElectrostatic Forces

Electrical gradientElectrical gradient

Opposite charges attract, Opposite charges attract,

Same charges repelSame charges repel

– Diffusion ForcesDiffusion ForcesConcentration gradientConcentration gradient

RESTING MEMBRANE RESTING MEMBRANE POTENTIALPOTENTIAL

Diffusion ForcesDiffusion Forces– NaNa++ and Cl and Cl-- in in– KK++ out out

Electrostatic ForcesElectrostatic Forces– NaNa++ and K and K++ in in– ClCl-- out out

++

MEMBRANE POTENTIALMEMBRANE POTENTIAL

Na+/K+ PumpNa+/K+ Pump– Compensatory Compensatory

MechanismMechanism– Active when Active when

intracellular Na+ highintracellular Na+ high– Neutral or inactive Neutral or inactive

when intracellular Na+ when intracellular Na+ lowlow

ACTION POTENTIALACTION POTENTIAL

ACTION POTENTIALACTION POTENTIAL

CONDUCTION OF A.P.CONDUCTION OF A.P.

SYNAPTIC TRANSMISSION SYNAPTIC TRANSMISSION

NEUROCHEMICAL SYNAPSESNEUROCHEMICAL SYNAPSES

SYNAPTIC COMMUNICATIONSYNAPTIC COMMUNICATION

POSTSYNAPTIC POSTSYNAPTIC POTENTIALSPOTENTIALS– Excitatory PSPExcitatory PSP– Inhibitory PSPInhibitory PSP

Electrical SynapsesElectrical Synapses– Gap junctionsGap junctions

Neurochemical Neurochemical SynapsesSynapses

Structures of Neurochemical SynapsesStructures of Neurochemical Synapses

Presynaptic Presynaptic MembraneMembrane

Postsynaptic Postsynaptic MembraneMembrane

Synaptic VesiclesSynaptic Vesicles

Synaptic CleftSynaptic Cleft

Receptor SitesReceptor Sites

Steps In Neurochemical TransmissionSteps In Neurochemical Transmission

SynthesisSynthesis

StorageStorage

Neurotransmitter ReleaseNeurotransmitter Release

Receptor ActivationReceptor Activation

Neurotransmitter DeactivationNeurotransmitter Deactivation– Enzymatic Deactivation (Metabolism)Enzymatic Deactivation (Metabolism)– ReuptakeReuptake

Steps in Neurochemical TransmissionSteps in Neurochemical Transmission

SYNTHESISSYNTHESIS

Receptor ActivationReceptor Activation

Ionotropic ReceptorsIonotropic Receptors– ligand gated ion channelsligand gated ion channels

Metabotropic ReceptorsMetabotropic Receptors– G proteinsG proteins– Second MessengersSecond Messengers

Neurotransmitter InactivationNeurotransmitter Inactivation Enzymatic Degradation (Metabolism)Enzymatic Degradation (Metabolism)

Acetylcholine is inactivated by an enzyme, Acetylcholine is inactivated by an enzyme, Acetylcholinesterase (AChE).Acetylcholinesterase (AChE).

The monoamines are inactivated by the The monoamines are inactivated by the enzyme, Monoamine Oxidase (MAO)enzyme, Monoamine Oxidase (MAO)

Catecholamines (DA, NE, E) are also Catecholamines (DA, NE, E) are also inactivated by and Catechol-O-inactivated by and Catechol-O-Methyltransferase (COMT).Methyltransferase (COMT).

ReuptakeReuptake The monoamines are also inactivated The monoamines are also inactivated

through reuptake.through reuptake.

MAJOR NEUROTRANSMITTERSMAJOR NEUROTRANSMITTERSAcetylcholineAcetylcholine MonoaminesMonoamines– CatecholaminesCatecholamines

EpinephrineEpinephrineNorepinephrineNorepinephrineDopamineDopamine

– IndoleaminesIndoleaminesSerotoninSerotonin

Amino Acid TransmittersAmino Acid Transmitters– Glutamate, AspartateGlutamate, Aspartate– GABA, GlycineGABA, Glycine

NeuropeptidesNeuropeptides– EnkephalinsEnkephalins– EndorphinsEndorphins

Cholinergic PathwaysCholinergic Pathways

Dopaminergic PathwaysDopaminergic Pathways

Noradrenergic PathwaysNoradrenergic Pathways

Serotonergic PathwaysSerotonergic Pathways

Neurochemical PathwaysNeurochemical Pathways

DopamineDopamine– Nigrostriatal Pathways (Substantia Nigra Nigrostriatal Pathways (Substantia Nigra

Basal Ganglia)Basal Ganglia)– Mesolimbic, Mesocortical Patways (VTA Mesolimbic, Mesocortical Patways (VTA

NAc and pfCTX)NAc and pfCTX)– Most widely studied neurobiology theory of Most widely studied neurobiology theory of

drug dependence relates to dopaminedrug dependence relates to dopamine

Neurochemical PathwaysNeurochemical Pathways

AcetylcholineAcetylcholine– Pontine nucleiPontine nuclei

involved in components of REM sleepinvolved in components of REM sleep

– Basal ForebrainBasal ForebrainReduced quantities found in Alzheimer’s patients Reduced quantities found in Alzheimer’s patients

NorepinephrineNorepinephrine– Locus Coeruleus Locus Coeruleus Forebrain Forebrain

Stimulant drugs may induce wakefulness through these Stimulant drugs may induce wakefulness through these pathwayspathways

Neurochemical PathwaysNeurochemical Pathways

Serotonin (5-HT)Serotonin (5-HT)– Raphe NucleiRaphe Nuclei– Research on weight control, aggressiveness, and Research on weight control, aggressiveness, and

depression are centered on 5-HTdepression are centered on 5-HT

GABAGABA– Widespread in CNSWidespread in CNS– Related to seizures Related to seizures

EndorphinsEndorphins– Spinal cord and midbrainSpinal cord and midbrain– Involved in body’s natural mechanisms for pain reliefInvolved in body’s natural mechanisms for pain relief