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Understanding Neuron Membrane Dynamics: Ion Channels, Action Potentials, and Synaptic Transmission

This article delves into the intricacies of neuron cell membranes, focusing on various ion channels such as voltage-gated and chemical-gated channels. Highlighting the role of ion gradients, it explains the phases of action potentials including depolarization and hyperpolarization. We explore the differences between excitatory and inhibitory postsynaptic potentials (EPSP and IPSP), including their effects on neuron firing. Furthermore, the significance of Na+/K+ pumps in maintaining concentration gradients is emphasized, alongside unmyelinated and myelinated propagation methods.

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Understanding Neuron Membrane Dynamics: Ion Channels, Action Potentials, and Synaptic Transmission

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  1. Animal Cell Chromatin

  2. Axonal Membrane of a Neuron

  3. Ion Channels • Cell membrane proteins that pass ions in and out of the cell • Voltage-Gated Ion Channels • gates are regulated by membrane voltage • Chemical-Gated Ion Channels (also called Receptors) • gates are regulated by neurotransmitters • Iontotropic • fast • Metabotropic (G-protein coupled) • requires second messenger cascade • slow

  4. Chemical-Gated Ion Channels Iontotropic Metabotropic

  5. Electrochemical Gradient • Inside the Cell • More K+ • Less Na+ • Outside the Cell • More Na+ • Less K+ • Ion Flow Mantra: Na+ In, K+ out

  6. Depolarization/Hyperpolarization

  7. 2 Action Potential Phases Rapid 3 1 Threshold 4 Phase Ion responsible Ion Channel Responsible 1. Threshold Na+ Chemical-gated Na+ channel 2. Rapid Depolarization Na+ Voltage-gated Na+ channel 3. Repolarization K+ Voltage -gated K+ channel 4. After Hyperpolarization K+ Na+/K+ pumps

  8. Na+/K+ Pumps After the Action Potential, Na+/K+ pumps move Na+ ions back out of the cell and move K+ ions back into the cell The movement is against the concentration gradient of each ion so it requires energy (ATP) The pumps move 3 Na+ ions for every 2 K+ ions

  9. Unmyelinated Propagation

  10. Myelinated Propagation

  11. Synaptic Action Voltage-gated Ca2+ channels • Synaptic Potentials: • EPSP • IPSP

  12. Synaptic Potentials • Excitatory Postsynaptic Potential (EPSP) • triggered by excitatory neurotransmitters • open ligand-gated Na+ channels • allows Na+ to flow inside the cell • causing a slight depolarization of the postsynaptic cell • moves the postsynaptic cell closer to firing an action potential • Inhibitory Postsynaptic Potential (IPSP) • triggered by inhibitory neurotransmitters • open ligand-gated K+ channels or Cl- channels • allows K+ to flow out of the cell or Cl- to flow inside the cell • causing a slight hyperpolarization of the postsynaptic cell • moves the postsynaptic cell further from firing an action potential

  13. The Battle to -55mV IPSP EPSP

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