resting membrane potential

• maintaining ion gradients

  sodium potassium pump (NA+/K+ ATPase)

  • needs atp
  • 3NA+ out and 2K+ in
• membrane potential

  ion concentration gradients result in separation of electrical charge across cell membrane

  • inside more negative than outside
  • Inside voltage (Vi) = -70mV
  • Outside voltage (Vo) = 0mV
  • Membrane potential (Em) = Vi – Vo
• maintaining resting membrane potential

  sodium potassium pump

  • maintains ion gradients
  • electrogenic - loses one positive on inside making inside more negative

  K+ leak channels

  • pores in membrane
  • K+ moves out cell down conc. gradient
  • net movement positive charge out cell
• function of membrane potential

  Homeostatic - maintains osmolarity

  rapid signalling and communication

  • action potentials
  • receptor potentials
  • post synaptic potentials

  energy source:

  • drives transmembrane transport processes
• Polarisation

  Depolarisation - membrane potential more positive

  Hyperpolarisation - potential more negative
• ion movement across semi - permeable membrane

  concentration gradient - high to low

  electrical gradient - attraction to opposite charge

  
• electrochemical equilibrium

  point at which number of ions moving along conc. gradient is equal to number moving along electrical gradient

  • overall no net movement X, where x is a specific ion
  • The membrane potential required to produce this electrochemical equilibrium for a specific ion is known as the equilibrium reversal potential, Ex - x is a specific ion

  REVERSAL POTENTIAL CALCULATED USING NERNST EQUATION

   
• NERNST EQUATION

  • usually biological systems so temp - 310K

  
• if membrane permeable to one type of ion

  membrane potential equals reversal potential

  = Nernstian
• Permeable to more than one type

  membrane potential does not equal reversal potential

  USE GOLDMAN-HODGKIN-KATZ (GHK) EQUATION

  P = permeability