Cell membrane potential

Question 1

Cell membrane potential: definition

Answer 1

• what enables nerves + muscles to function
• Possibility that sodium + potassium ions will be moved through the CM = only potential as have to go through channels and those channels are gated

Question 2

Ions + how they move through the CM

Answer 2

• Ions like sodium, potassium + chloride can move through the CM if the gated channels are open.
• Each ion has its own specific gated channel.
• Some K+ channels are always open, so K+ is always diffusing out of the cell.
  - The concentration gradient favours K+ leaving the cell
• The membrane of most cells is also slightly permeable to Na+ (but much less than for K+).
• Some Na+ can move into the cell, but is much less than the amount of K+ leaving the cell
• Because more K+ is leaving the cell than Na+ is entering, the inside of the cell becomes negatively charged compared to the outside = that negative charge is what we called the cell membrane potential = which forms the basis of nerve info transmission + muscle contraction
  
  • The electrical gradient favours K+ remaining in the cell.
• An equilibrium is reached when the concentration gradient is balanced by the electrical gradient.
• This sets up the membrane potential
  - the membrane potential is a voltage - the difference in charge b/w two points
  - because there is a voltage the membrane is ‘polarised’.
• The membrane potential is –50 to –90 mV in most cells.
  - The inside of the cell is negatively charged compared to the outside.