PMT actionpotential

• 1. What happens upon stimulation?

  Axon membrane becomes depolarised.
• 1. How does the axon membrane become depolarised?

  Firstly, the EXCITATION of the neurone cell, TRIGGERED BY A STIMULUS, causes the SODIUM ION CHANNELS to OPEN , as a result of making it more PERMEABLE to sodium ions

  • the sodium ions now diffuse into the the axon down the electrochemical gradient, thus makes the inside LESS NEGATIVE
• 2. What happens upon reaching the threshold of -55mV?

  Even more sodium ion channels open, eventually giving a potential difference of +40mV.

  • This is the END OF DEPOLARISATION. Now repolarisation starts
• 3. How is repolarisation achieved?

  As a result of sodium ion channels CLOSING and potassium ion channels OPENING.

  • The K+ions diffuse out of the neurone down the conc gradient and eventually RESTORE THE RESTING POTENTIAL.
  • However, as the closing of the k+ion channels is slightly delayed, this leads to HYPERPOLARISATION
• What is hyperpolarisation?


  When the potential difference becomes more negative than the resting potential
• Hyperpolarisation- how is the resting potential then achieved?

  With help of sodium-potassium pump which returns the potential difference to -70mV