Chapter 8c Neurons Cellular and Network Properties 2013 Pearson Education Inc Figure 8 24a ESSENTIALS Summation Summation of several subthreshold signals results in an action potential Presynaptic axon terminal Trigger zone Three excitatory neurons fire Their graded potentials separately are all below threshold Graded potentials arrive at trigger zone together an sum to create a suprathreshold signal Action potential An action potential is generated Figure 8 24a ESSENTIALS Summation Slide 1 Presynaptic axon terminal Three excitatory neurons fire Their graded potentials separately are all below threshold Trigger zone Action potential 2013 Pearson Education Inc Figure 8 24a ESSENTIALS Summation Slide 2 Presynaptic axon terminal Three excitatory neurons fire Their graded potentials separately are all below threshold Trigger zone Graded potentials arrive at trigger zone together and sum to create a suprathreshold signal Action potential 2013 Pearson Education Inc Figure 8 24a ESSENTIALS Summation Slide 3 Presynaptic axon terminal Three excitatory neurons fire Their graded potentials separately are all below threshold Trigger zone Graded potentials arrive at trigger zone together and sum to create a suprathreshold signal Action potential An action potential is generated 2013 Pearson Education Inc Figure 8 24b ESSENTIALS Summation Postsynaptic inhibition An inhibitory presynaptic neuron prevents an action potential from firing Inhibitory neuron 1 2 Trigger zone One inhibitory and two excitatory neurons fire 1 2 No action potential The summed potentials are below threshold so no action potential is generated Figure 8 24b ESSENTIALS Summation Slide 1 Inhibitory neuron Trigger zone One inhibitory and two excitatory neurons fire 2013 Pearson Education Inc No action potential Figure 8 24b ESSENTIALS Summation Slide 2 Inhibitory neuron Trigger zone One inhibitory and two excitatory neurons fire No action potential The summed potentials are below threshold so no action potential is generated 2013 Pearson Education Inc How Synapses Work BioFlixTM How Synapses Work 2013 Pearson Education Inc Figure 8 24c ESSENTIALS Summation No summation Two subthreshold graded potentials will not initiate an action potential if they are far apart in time Stimuli X1 X2 V m l a i t n e t o p e n a r b m e M 55 70 Threshold A1 A2 X1 X2 Time msec Figure 8 24d ESSENTIALS Summation Stimuli X1 X2 Summation causing action potential If two subthreshold potentials arrive at the trigger zone within a short period of time they may sum and initiate an action potential 30 0 55 70 V m l a i t n e t o p e n a r b m e M Threshold A2 A1 X1 X2 Time msec Figure 8 25 A THREE DIMENSIONAL RECONSTRUCTION OF DENDRITIC SPINES AND THEIR SYNAPSES Excitatory synapses red Spine head Spine neck Inhibitory synapses blue Spines Figure 8 26a 1 of 9 In presynaptic inhibition an inhibitory neuron synapses on one collateral of the presynaptic neuron and selectively inhibits one target Excitatory neuron Action potential Inhibitory neuron Presynaptic axon terminal No neurotransmitter release Target cell No response Neurotransmitter released Response Response An excitatory neuron fires An action potential is generated An inhibitory neuron fires blocking neurotransmitter release at one synapse Inhibitory neuron Presynaptic axon terminal No neurotransmitter release Target cell Action potential Neurotransmitter released Slide 1 No response Response Response Figure 8 26a 1 of 9 Excitatory neuron An excitatory neuron fires 2013 Pearson Education Inc Inhibitory neuron Presynaptic axon terminal No neurotransmitter release Target cell Action potential Neurotransmitter released Slide 2 No response Response Response An excitatory neuron fires An action potential is generated Figure 8 26a 1 of 9 Excitatory neuron 2013 Pearson Education Inc Inhibitory neuron Presynaptic axon terminal No neurotransmitter release Target cell Action potential Neurotransmitter released Slide 3 No response Response Response An excitatory neuron fires An action potential is generated An inhibitory neuron fires blocking neurotransmitter release at one synapse Figure 8 26a 1 of 9 Excitatory neuron 2013 Pearson Education Inc Figure 8 26b 5 of 9 In postsynaptic inhibition all targets of the postsynaptic neuron are inhibited equally Inhibitory neuron modifies the signal IPSP EPSP Excitatory neuron No response No response No response One excitatory and one inhibitory presynaptic neuron fire Modified signal in postsynaptic neuron below threshold No action potential initiated at trigger zone No response in any target cell Inhibitory neuron modifies the signal Figure 8 26b 5 of 9 IPSP EPSP Excitatory neuron One excitatory and one inhibitory presynaptic neuron fire 2013 Pearson Education Inc Slide 1 No response No response No response Figure 8 26b 5 of 9 Inhibitory neuron modifies the signal IPSP EPSP Excitatory neuron One excitatory and one inhibitory presynaptic neuron fire Modified signal in postsynaptic neuron below threshold 2013 Pearson Education Inc Slide 2 No response No response No response Figure 8 26b 5 of 9 2013 Pearson Education Inc Inhibitory neuron modifies the signal IPSP EPSP Excitatory neuron One excitatory and one inhibitory presynaptic neuron fire Modified signal in postsynaptic neuron below threshold No action potential initiated at trigger zone Slide 3 No response No response No response Figure 8 26b 5 of 9 Inhibitory neuron modifies the signal IPSP EPSP Excitatory neuron Slide 4 No response No response No response One excitatory and one inhibitory presynaptic neuron fire Modified signal in postsynaptic neuron below threshold No action potential initiated at trigger zone No response in any target cell 2013 Pearson Education Inc Interactive Physiology Animation Synaptic Potentials and Cellular Integration Integration Long Term Potentiation and Depression Activity at a synapse induces sustained changes in quality or quantity of connections Glutamate is key element in potentiation May be related to learning memory depression and mental illness 2013 Pearson Education Inc Figure 8 27 LONG TERM POTENTIATION Presynaptic axon Glutamate Na Ca2 Mg2 Glutamate binds to AMPA and NMDA channels Net Na entry through AMPA channels depolarizes the postsynaptic cell Depolarization ejects Mg2 from NMDA receptor channel and opens channel AMPA receptor Na Paracrine release Ca2 NMDA receptor Ca2 enters cytoplasm through NMDA channel Ca2 activates second messenger pathways Postsynaptic cell