Describe and explain the role of positive feedback in an action potential

Describe:·     Random or small amount of sodium ions enter the axon (diffusion) which leads to a slight depolarisation of the membrane·     Down the concentration gradient (more sodium outside the cell than inside)·     Depolarisation – membrane potential gets more positive (away from resting)·     As membrane depolarises voltage gated sodium channels open (range of membrane potentials that different voltage gated sodium channels open at)·     This allows more sodium ions to enter as membrane becomes more permeable (low resting permeability to sodium)·     Greater depolarisation which ensures the membrane potential reaches threshold which leads to an action potential being triggeredo  Ensures that signals get communicated well
Explain: why is positive feedback used?·     However, positive feedback is an unstable system – can get out of control so there are measures to ensure that this doesn’t happen:o  Sodium-potassium pumpo  Response ends via a time dependent method of closing the channel·     Why the positive feedback system is used?o  So a signal definitely leads to a response and enables communicationo  Amplificationo  Ensures that the response is strong enough to elicit a response at the endo  If it was a negative feedback system, the response would cause the membrane potential to return to rest without an action potential being triggered (Which is what happens if not a strong enough stimulus is applied – decays passively)o  Positive feedback ensures an action potential is triggered