Resting Membrane Potential and Depolarization

Resting Membrane Potential (RMP)

  • Definition of RMP:

    • The Resting Membrane Potential (RMP) of a neuron is approximately -70 mV.

  • Why is there a voltage difference?

    • The voltage difference exists due to the unequal distribution of ions across the cell membrane.

  • Role of Leak Channels:

    • There are leak channels in the neuron's membrane that allow the passage of ions.

    • Potassium ions ($K^+$) leak out of the cell more easily than sodium ions ($Na^+$) can leak in.

  • Sodium/Potassium Pump Functionality:

    • The sodium/potassium pump (Na-K pump) plays a crucial role in maintaining concentration gradients of ions.

    • This pump transports 3 sodium ions ($Na^+$) out of the cell for every 2 potassium ions ($K^+$) it brings into the cell.

    • As a result, there is a net movement of more positive ions ($K^+$ leaks out) than what is brought back in ($Na^+$ leaks in).

  • Net Effect on Charge Distribution:

    • More positive charges accumulate on the outside surface of the cell membrane compared to the inside.

    • This accumulation generates the voltage difference across the membrane.

  • Concentration Gradients Maintenance:

    • The Na-K pump continuously returns ions to the side of the membrane where they originated, thus maintaining concentration gradients essential for the resting membrane potential.

  • Condition of the Cell:

    • The inside of the cell is negatively charged relative to the outside, maintaining the polarized state of the cell.

    • The cytoplasm of the cell is neutral.

    • The extracellular space is neutral.

Depolarization of the Membrane

  • Definition of Depolarization:

    • Depolarization refers to a change in the Resting Membrane Potential where the inside of the cell becomes more positive than its resting state.

  • Example of Depolarization:

    • A change in voltage from -70 mV to -65 mV indicates depolarization.

  • Mechanism for Current Flow:

    • Electrical current is generated by depolarizing the membrane.

    Visual Representation (Hypothetical Data)

  • Graph of Membrane Potential over Time:

    • Membrane potential (mV)

    • Inside positive -> 0 mV

    • Inside negative is observed between -50 mV to -100 mV

  • Stimulus example:

    • The presence of dopamine can serve as a depolarizing stimulus.

  • Time Progression of Depolarization:

    • Temporal progression of electrical current over time (ms) can be noted in a graph format indicating changes in membrane potential.

  • Final Note:

    • Understanding the dynamics of resting membrane potential and depolarization is essential for grasping the fundamentals of neuron functioning and electrical signaling.