non-myelinated

• Once the threshold is reached an action potential moves along the axon. 

  The movement id the reversal of electrical charge at different points along the axon membrane. The size of the charge is constant
• At resting potential the axon is polarised. 
• A stimulus causes some sodium ions voltage gated channels to open, and lots of sodium ions move into the axon by facilitated diffusion - the axon becomes depolarised. 
• The sodium ions cause the opening of more sodium ion voltage gated channels further along the axon - depolarisation in the next region. 
• When the membrane potential reaches + 40 mV, the sodium ions voltage gated channels and the potassium voltage gated channels are open. 
• Potassium ions diffuse out of the axon 
• The diffusion of potassium ions is fast and the potassium voltage gated channels close. - 80 mV 
• There is a temporary overshoot as too many potassium ions move out - hyperpolarisation 
• Potassium ion gates close and the potassium/sodium ion pump re-establishes the resting potential of - 70 mV - repolarisation 
• The refractory period is a period of recovery allowing a time delay between action potentials. Ion channels are recovering and cant be forced open. It ensures that action potentials don’t overlap and that they are unidirectional. 
• A bigger stimulus wont cause a bigger action potential, just more frequent action potentials - all or nothing principle. 
• When not enough sodium ions don’t reach the threshold, no response occurs.