Notes on Membrane Potential and Action Potentials

Membrane Potential and Action Potentials

• Resting Potential

  • The membrane potential of a neuron at rest, typically around -70 mV.
  • Maintained by the sodium-potassium pump, which exchanges 3 Na+ ions out of the neuron for 2 K+ ions into the neuron.

• Threshold Potential

  • The critical level to which a membrane potential must be depolarized to initiate an action potential (typically around -55 mV).

• Action Potential

  • A rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane.
  • Occurs when the membrane depolarizes past the threshold potential.

• Summation of Inputs

  • Neurons receive numerous inputs; the combined effects can lead to depolarization past threshold.

  • Summation can occur in different forms:

  • a. Subthreshold, No Summation

    • Individual excitatory postsynaptic potentials (EPSPs) do not reach threshold.

  • b. Temporal Summation

    • Inputs from the same source occur in rapid succession, adding together to exceed threshold.

  • c. Spatial Summation

    • Inputs from multiple sources occur simultaneously, enough to reach threshold.

  • d. Spatial Summation of EPSP and Inhibitory Postsynaptic Potential (IPSP)

    • Combination of EPSP and IPSPs potentially leads to a net effect, determining if action potential is generated.

• E₁ and E₂ Notation

  • Represent different excitatory or inhibitory postsynaptic potentials affecting the postsynaptic neuron.