Trigger zone: Depolarization is needed to excite (cause an action potential) a nerve cell. • excitatory postsynaptic potential (EPSP) : a depolarizing graded potential which drives the membrane potential towards threshold. • inhibitatory postsynaptic potential (IPSP) : a hyperpolarizing graded potential which drives the membrane potential away from threshold. • If multiple signals arrive at the trigger zone they are summed (superimposed). If multiple stimuli arrive simultaneously this is call spatial summation , if the arrive at slightly different times you have temporal summation . THE NERVOUS SYSTEM Chapter 8: Neurons: cellular and network properties Part D. Action Potentials: Action potentials are rapid signals that pass along the axon to the axon terminal, and differ from graded potentials in several ways: (Figure 8-9) 1) Action potentials are identical to each other and 2) they do not diminish in strength as they travel through the cell. The action potential is a large depolarizing signal up to 110 mV in amplitude.
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