The Resting Potential - Diffusion
- Diffusion is the movement of particles from an area of high concentration to an area of low concentration, i.e., "down the concentration gradient." This is a passive process, which means it happens without consuming energy. The brain does need to do work, or "burn sugar", to accomplish this.
- A permeable membrane lets everything pass, and therefore everything diffuses across the membrane. A semipermeable membrane lets only certain things pass, so some particles diffuse across the membrane while others are trapped on one side of it. The axon membrane is a semipermeable membrane.
- If the diffusing particles are ions (charged), then diffusion through a semipermeable membrane can establish a separation of charges across the membrane. The membrane becomes electrically polarized, and a voltage can be measured across it. This adds electrostatic force to the "force" of diffusion.
- Neither force can be made "happy" since they usually act in opposite directions. An equilibrium must be reached between them in which the "force" of diffusion acting in one direction exactly balances the electrostatic force acting in the other direction. This is what happens across the nerve cell membrane.
