Action potential

• There are channel proteins in the axon membranes that allow sodium ions or potassium ions to pass through
• Voltage gate channel proteins

  Channel proteins that open and close depending on the electrical potential (voltage) across the axon membrane
• Channel proteins are closed when at resting
• Action potential stimulation in a neuron

  1. Sodium channel proteins open

  2. Sodium ions pass into the axon

  3. Inside becomes less negative (depolarization)

  4. Triggers more sodium channels to open

  5. Action potential is generated
• Electrochemical gradient

  Greater sodium ion concentration outside than inside the axon
• Inside of the axon is negatively charged, attracting positively charged sodium ions
• Positive feedback

  Small initial depolarization leads to greater levels of depolarization
• If potential difference reaches around –50V (threshold value), many more channels open
• Many more sodium ions enter causing the inside of the axon to reach a potential of around +30V
• Action potential is generated
• Depolarization of the membrane at the site of the first action potential


  Causes current to flow to the next section of the axon membrane
• Flow of current is caused by the diffusion of sodium ions along the axon from an area of high concentration to an area of low concentration
• Action potential propagation

  1. Triggers production of another action potential

  2. Process continues along the axon
• In the body, this allows action potentials to begin at one end of an axon and then pass along the entire length of the axon membrane