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How does the EPSP or IPSP travel towards the axon hillock?
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[QUOTE="TytoAlba95, post: 6198204, member: 647883"] My concepts so far: EPSP and IPSP are membrane potentials generated due to the opening of ligand-gated ion channels.EPSPs are membrane potentials that are well below the threshold potential, generated due to the influx of Na or Ca ions(depolarisation).IPSP are membrane potentials that are due to hyperpolarization of the membrane caused by the influx of Cl- or efflux of K, in the cell body. 1. Now, do these potentials travel in the same way as action potential in the axon? In case of an EPSP, say for example, a ligand-gated sodium channel got opened and Na rushed into the cytoplasm. As a result, the local positive charges (that were already in the cytoplasm) will experience a strong repulsive force and will travel away from the channel. This local flow of current will depolarise (make the membrane potential less negative) the adjacent membrane and if the potential reaches the threshold potential only then an Action Potential will be generated. But an EPSP usually doesn't generate a threshold potential. EPSPs from different synapses generate a total current which depolarises the axon hillock/ initial segment to reach the threshold potential, and an Action potential is generated. In case of IPSP, the influx of negative charge cause the adjacent membrane to hyperpolarize in a similar way, inhibiting stimulation, as the membrane potential at Axon hillock drops far from the threshold potential. 2. During axonal propagation, the impulse once travels in forward direction. It doesn't travel backward because the Na-channels cannot be immediately excited, as they need to change from inactive to closed state to be reactivated (refractory period). But what happens in the cell body ? Do the depolarization (EPSPs) and hyperpolarization (IPSPs) travel backward? 3. Is the threshold potential at the axon hillock/initial segment less than that of the nodes of ranvier? Why is it so? [/QUOTE]
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How does the EPSP or IPSP travel towards the axon hillock?
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