11.8 Postsynaptic Potentials

11.8 Postsynaptic Potentials • Neurotransmitter receptors cause graded potentials that vary in strength based on: – Amount of neurotransmitter released – Time neurotransmitter stays in cleft • Depending on effect of chemical synapse, there are two types of postsynaptic potentials – EPSP: excitatory postsynaptic potentials – IPSP: inhibitory postsynaptic potentials Postsynaptic Potentials and Their Summation (1 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Excitatory Synapses and EPSPs • Neurotransmitter binding opens chemically gated channels – Allows simultaneous flow of Na+ and K+ in opposite directions • Na+ influx greater than K+ efflux, resulting in local net graded potential depolarization called excitatory postsynaptic potential (EPSP) • EPSPs trigger AP if EPSP is of threshold strength – Can spread to axon hillock and trigger opening of voltage-gated channels, causing AP to be generated Postsynaptic Potentials and Their Summation (2 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Inhibitory Synapses and IPSPs • Neurotransmitter binding to receptor opens chemically gated channels that allow entrance/exit of ions that cause hyperpolarization – Makes postsynaptic membrane more permeable to K+ or Cl–  If K+ channels open, it moves out of cell  If Cl– channels open, it moves into cell – Reduces postsynaptic neuron’s ability to produce an action potential  Moves neuron farther away from threshold (makes it more negative) Postsynaptic Potentials and Their Summation (3 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Integration and Modification of Synaptic Events (1 of 4) • Summation by the postsynaptic neuron – A single EPSP cannot induce an AP, but EPSPs can summate (add together) to influence postsynaptic neuron  IPSPs can also summate – Most neurons receive both excitatory and inhibitory inputs from thousands of other neurons  Only if EPSPs predominate and bring to threshold will an AP be generated – Two types of summations: temporal and spatial Integration and Modification of Synaptic Events (2 of 4) – Temporal summation  One or more presynaptic neurons transmit impulses in rapid-fire order – First impulse produces EPSP, and before it can dissipate another EPSP is triggered, adding on top of first impulse – Spatial summation  Postsynaptic neuron is stimulated by large number of terminals simultaneously – Many receptors are activated, each producing EPSPs, which can then add together Postsynaptic Potentials and Their Summation (4 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Postsynaptic Potentials and Their Summation (5 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Postsynaptic Potentials and Their Summation (6 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Postsynaptic Potentials and Their Summation (7 of 7) Focus Figure 11.4 Postsynaptic Potentials and Their Summation. Figure Animation: Comparison of Graded Potentials and Action Potentials Click here to view ADA compliant Animation: Comparison of Graded Potentials and Action Potentials Integration and Modification of Synaptic Events (3 of 4) • Synaptic potentiation – Repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron  Ca2+ concentration increases in presynaptic terminal, causing release of more neurotransmitter  Leads to more EPSPs in postsynaptic neuron – Potentiation can cause Ca2+ voltage gates to open on postsynaptic neuron  Ca2+ activates kinase enzymes, leading to more effective response to subsequent stimuli – Long-term potentiation: learning and memory Integration and Modification of Synaptic Events (4 of 4) • Presynaptic inhibition – Release of excitatory neurotransmitter by one neuron is inhibited by another neuron via an axoaxonal synapse – Less neurotransmitter is released, leading to smaller EPSPs The Endomembrane System (1 of 4) Table 11.3-1 Comparison of Graded Potentials and Action Potentials. The Endomembrane System (2 of 4) Table 11.3-2 Comparison of Graded Potentials and Action Potentials. The Endomembrane System (3 of 4) Table 11.3-3 Comparison of Graded Potentials and Action Potentials. The Endomembrane System (4 of 4) Table 11.3-4 Comparison of Graded Potentials and Action Potentials.