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Synaptic Potentials

Synaptic Potentials. B.Sc 2002. Summation of EPSPs. Unless cell is already bombarded with other epsps, spatial or temporal summation is necessary to trigger an action potential

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Synaptic Potentials

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  1. Synaptic Potentials B.Sc 2002

  2. Summation of EPSPs • Unless cell is already bombarded with other epsps, spatial or temporal summation is necessary to trigger an action potential • Motoneurones may be constantly affected by subthreshold inputs…concept of a ‘resting potential’ for a central nerve cell may be erroneous

  3. Electrotonus • Synapses near or on cell body produce large EPSP’s with sharply rising front edges • Synapses on distal dendrites produce smaller EPSP’s with slowly rising front edges • Different input axons can form synapses at different distances on dendrites; giving different EPSP shapes

  4. There are multiple synaptic boutons for each functional synapse • There is evidence that not all boutons release transmitter with each arriving action potential • This could be reason for variability in EPSP’s from a single axon

  5. Inhibitory synapses • An inhibitory synapse does not have to produce an IPSP to be effective • Reducing membrane resistance proximal to an excitatory synapse effectively shunts excitatory synaptic current out of cell and stops it reaching axon hillock • Presynaptic inhibition does not produce IPSPs

  6. Mixed pre-and post-synaptic inhibition • GABA-B receptors may terminate glu transmission by blocking glu release & speeding up repolarisation of terminal • GABA-A receptors hyperpolarise post-synaptic membrane net effect is to decrease ‘synaptic refractory period’ • This may increase maximum rate of transmission

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