1) Nerve impulses propagate along axons via the movement of sodium and potassium ions across the axon membrane. 2) At rest, the axon maintains a negative charge due to higher concentrations of potassium and organic ions inside the axon and higher concentrations of sodium and chloride ions outside. 3) When an impulse is generated, the permeability of the axon membrane to sodium briefly increases, allowing sodium to flow inside and depolarize the membrane. This creates an electrical signal called an action potential.

4. Nerve impulse (resting state) Exclusive to inside Organic ions Greater Cl- Greater K+ Greater Na+ Outside the axon Inside the axon Ions region of axon

8. Action potential