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Lecture 4

Neuro Lecture 4.docx

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Michelle French

Neuro: Lecture 4 October-28-12 12:47 PM Post synaptic receptors •Transmitter agent diffuses across synapse and binds to a specific site on a receptor protein embedded in post synaptic membrane •Binding of transmitter causes a change in the shape of the receptor protein •Receptors can be o Ionotropic (directly opens channels) o Metabotropic (initiates a metabolistic cascade to activate enzymes •Receptor determines effect, not transmitter Ionotropic effects •Ligand binding opens an ion channel •Binding of the transmitter to the post synaptic membrane results in change in the post synaptic membrane potential, called post synaptic potential •The duration of PSP is about 20-40ms (as long as the transmitters are present) •Ion channel may be specific for cations (NA, K) - EPSP (depolarizing) excitatory- more likely to generate action potential •Or ion channel may be specific for Cl or K ion - IPSP - inhibiting post synaptic potential (hyperpolarizing), less likely to generate AP •Eg. Nitcotinic receptor for Acetylcholine •Ligands used o Acetylcholine (ACh ) - nitcotinic receptor o Glutamate o GABA (inhibitory generates IPSPs) o Glycine • All these ligands can also act on metabotropic receptors - Receptor matters, not transmitter Metabotropic effects •Ligand binding leads to G protein coupled enzyme •The enzyme then destroys or promotes second messengers o cAMP, cGMP, IP3 o 2nd messengers then activate other enzymes o If you phosphorylate membrane proteins (i.e. ion channels) result in modulation of ion currents •Ionotropic faster (opens ion channels) •Metabotropic takes time •But, don`t need change in MP, could be all internal •Change in MP WILL develop, but very slowly (slow EPSP, IPSP) •Change is slow because has to go through all the enzyme work first Beta- adrenoreceptor •Metabolic receptor for noradrenalin (NA) •Binding of NA to beta receptor activate adenylyl cyclase via G protein alteration •Adenylyl cyclase increases production of cAMP •cAMP activates kinases which phosphorylate membrane Ca++ channel •Leads to increase in Ca++ efflux o Important to heart muscle as increases contractility •Beta blockers Ligands for metabotroic receptors •ACh: muscarinic receptor •Peptides: substance P, beta endorphin ADH •Catecholamines: noradrenaline, dopamine •Serotonin •Putines (adenosine, ATP) •Gases: NO, CO Spread of PSPs •Generated in inexcitable membrane: o Neuronal dendrites and cell bodies o These areas do not have high density of voltage gated Na+ channels o They cannot gene
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