Sodium and Potassium Action Potential

1. Overview of Resting Potential

   • The resting potential of a neuron is maintained by the sodium-potassium pump.

   • Sodium-Potassium Pump Function:

     • Pumps out three sodium ions (Na⁺) and brings in two potassium ions (K⁺) simultaneously.

     • This creates a concentration gradient necessary for action potentials.

2. Action Potential Generation

   • Stimulus Effect

     • An external stimulus leads to a slight depolarization of the membrane.

     • The initial bump on the graph indicates this stimulus effect.

   • Opening of Ion Channels

     • Upon receiving a stimulus:

     • Sodium Channels (voltage-gated AND mechanical): Open rapidly in response to depolarization. AT 55mV

     • Potassium Channels (voltage-gated AND mechanical): Open more slowly than sodium channels. AT 55mV

     • The influx of Na⁺ leads to a rapid increase in membrane potential.

   • Membrane Potential Change:

     • Membrane potential reaches +55 mV (threshold potential) due to sodium influx.

   • Voltage Threshold and Changes

     • At +55 mV (threshold potential):

     • Both sodium and potassium voltage-gated AND Mechanical channels fully open.

     • Sodium influx continues, causing the cell to become more positive.

     • Membrane potential reaches a peak of +30 mV:

     • At this point, sodium channels are closing, which halts the further influx of Na⁺.

     • Sodium channels close quickly after opening, contributing to rapid changes in membrane potential.

3. Repolarization Phase

   • Potassium Ion Movement

     • At +30 mV:

     • Potassium channels are fully open; K⁺ begins to exit the cell following its concentration gradient.

     • So n K⁺ flows from an area of high concentration inside the cell to lower concentration outside.

     • The efflux of K⁺ causes the membrane potential to decrease, resulting in repolarization and hyperpolarization.

   • Effects of Potassium Exit

     • Continued exit of K⁺ can result in a more negative potential than the resting state, temporarily hyperpolarizing the membrane.

     • Hyperpolarization occurs due to the fact that potassium channels close more slowly than sodium channels, leading to potential values of less than -70 mV.

4. Return to Resting Potential

   • Re-establishing Resting Potential

     • After repolarization, the membrane potential is below resting state (around -70 mV):

     • Once potassium channels close completely,

     • The sodium-potassium pump resumes its activity.

     • It pumps in three Na⁺ ions for every two K⁺ ions expelled, resetting the ion concentrations.

     • The neuron returns to its resting potential, ready to respond to subsequent stimuli.

   • Cycle Repeats

     • This entire process can repeat with further stimuli, leading

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