The dotted, blue channels represent sodium channels the striped, green channels represent potassium channels the solid yellow channels represent chloride channels. After the stimulus, the ion channels close, and the membrane potential returns to rest. This causes an excitatory depolarization called an excitatory postsynaptic potential (EPSP). When a stimulus opens sodium channels, sodium rushes into the cell because the equilibrium potential of sodium is +60 mV. If there is not another stimulus, the cell will return to the resting membrane potential.Īnimation 5.2. Therefore, an EPSP is an excitatory change in the membrane potential of a postsynaptic neuron.Ī postsynaptic potential is typically brief, with ion channels closing quickly after the stimulus occurs. This depolarization increases the likelihood a neuron will be able to fire an action potential, which makes this ion flow excitatory. At 0 mV, there is no potential or polarization across the membrane, so moving toward 0 would be a decrease in potential. This change is called a depolarization because the cell’s membrane potential is moving toward 0 mV, and the membrane is becoming less polarized. When sodium brings its positive charge into the cell, the cell’s membrane potential becomes more positive, or depolarizes. The electrochemical gradient drives sodium to rush into the cell. Excitatory Postsynaptic Potentials (EPSPs)Īn excitatory postsynaptic potential (EPSP) occurs when sodium channels open in response to a stimulus. ‘Postsynaptic Ion Flow’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. A stimulus can cause ion channels in the membrane of the cell body or dendrites to open, allowing ion flow across the membrane. The change in membrane potential in response to the stimulus will depend on which ion channels are opened by the stimulus.Īnimation 5.1. A stimulus can range from neurotransmitters released by a presynaptic neuron, changes in the extracellular environment like exposure to heat or cold, interactions with sensory stimuli like light or odors, or other chemical or mechanical events. Ion channels that are opened by a stimulus allow brief ion flow across the membrane. For our purposes, postsynaptic potentials are measured in the dendrites and cell bodies. Postsynaptic potentials are changes in membrane potential that move the cell away from its resting state. This chapter will examine ion flow through these channels after a stimulus and how the membrane potential changes in response. We will cover how these channels open in a later lesson. However, the ability of neurons to function properly and communicate with other neurons and cells relies on ion flow through channels other than the non-gated leak channels. When the neuron is at rest, there is a baseline level of ion flow through leak channels.
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