• Neurones?transmit?electrical impulses, which travel extremely quickly along the neurone?cell surface membrane?from one end of the neurone to the other
• In a?resting axon?(one that is?not transmitting impulses), the?inside?of the axon always has a?negative electrical potential?compared to outside the axon
  • This is called the?resting potential

   

• This?potential difference?when there are no impulses is usually about?-70mV?(ie. the inside of the axon has an electrical potential about 70mV?lower?than the outside)
• Two factors contribute to establishing and maintaining the resting potential:
  • The active transport of sodium ions and potassium ions
  • Differential membrane permeability

   

The active transport of sodium ions and potassium ions

• Carrier proteins called sodium-potassium pumps are present in the membranes of neurones
• These pumps use?ATP?to actively transport?3 sodium ions out?of the axon for every?2 potassium ions?that they actively transport in
• This means that there is a larger concentration of positive ions outside the axon than there are inside the axon
• The movement of ions via the sodium-potassium pumps establishes an?electrochemical gradient

A differential membrane permeability

• The cell-surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move across the membrane by facilitated diffusion
• The protein channels are?less permeable to sodium ions?than potassium ions
• This means that potassium ions can diffuse back down their concentration gradient, out of the axon, at a?faster rate?than sodium ions

The resting potential of an axon and how it is maintained