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Depolarization of the Postsynaptic Neuron Membrane

  • While the postsynaptic neuron is at rest, Na+ / K+ pump proteins actively concentrated Na+ ions outside the cell and K+ ions inside the cell. Many of the K+ ions diffused back across the membrane through leak channels, making the cell’s interior relatively negative (polarized to -70mV).
  • Depolarization of the postsynaptic membrane begins when ACh is released by the presynaptic neuron and image descriptionbinds to receptors in the postsynaptic membrane.
  • Chemical gates image descriptionopen in response and the┬áreceptors form water-filled channels, which Na+ and K+ ions pass through.
  • Because of favorable diffusion and electrical gradients, more Na+ ions image descriptionenter the cell than K+ ions image descriptionexit.
  • A gain in positive ions inside the postsynaptic neuron causes it to image descriptiondepolarize (excitatory postsynaptic potential or EPSP).
  • The amount of depolarization is graded (variable) and depends on how many ACh molecules bind to the postsyaptic receptors and how many ions are exchanged.