Notes on 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.