Potential Difference Across a Cell Plasma Membrane

• Plasma membrane of all cells, including plant cells, has an unequal ion distribution across it; there are large anions (negatively charged ions) in cytoplasm which are too large to pass out
• Phospholipid bilayer is also impermeable to Na^+ and K^+ ions as they are charged; however, there are pumps in membrane actively transporting 3 Na^+ out to 2 K^+ in, goes against concentration gradient
• Neurone plasma membrane contains Na^+ and K^+ voltage gated protein channels; may be open or shut, they affect potential difference across plasma membrane
• All plasma membranes have potential difference across them, -70mV, it is only in neurone where potential difference can change
• Threshold potential is potential difference across membrane, that must be reached during depolarisation, to achieve action potential (around -55mV)
• Sodium-Potassium Pump

  A) Na^+

  B) K^+

  C) P_i

  D) ATP

  E) ADP

  F) K^+

  G) P_i

  H) Na^+

  I) P_i

  
• Gated Channels

  
• Graph: All action potentials cause same membrane potential changes (70mV to 40mV) so action potential frequency increases if stimulus strength increases (not size)

  A) Action Potential

  B) Threshold

  C) Depolarisation

  D) Stimulus

  E) Repolarisation

  F) Refractory Period

  G) Resting State

  H) Failed generator potentials

  I) Na^+

  J) K^+