the nerve impulse

• How is resting potential maintained

  1. Na+ is actively transported out of the neurone

  2. K+ is transported into the neurone

  3. For every 3 Na+ ions pumped out, 2 K+ ions are pumped in (by a sodium-potassium pump) so cytoplasm is more negative

  4. K+ also diffuses out of the cell by facilitated diffusion through open K+ channels and Na+ diffuses into the cell through open Na+ channels

  5. but membrane is more permeable to potassium
• the charge inside an axon at rest

  -70 mV
• state of axon membrane in resting potential

  polarised
• state of axon membrane in action potential

  Depolarised
• charge inside axon in action potential

  +40mV
• Describe the process of an action potential

  1. energy from stimulus causes sodium voltage gated channels to open and sodium ions to diffuse into axon

  2) this causes the membrane to depolarise

  3) as sodium ions diffuse into axon, more sodium channels open

  4) once reaching +40 mV, sodium channels close and potassium channels open

  5) membrane becomes more polarised

  6) diffusion of potassium ions overshoots gradient leading to hyperpolarisation and the potassium channels close
• What causes more sodium channels to open in an action potential?

  formation of localised current established by influx of sodium ions
• Define saltatory conduction

  action potential jumps from node to node
• Passage of action potential along myelinated axon

  1. action potentials can only occur at nodes of Ranvier

  2) localised currents arise

  3) action potential can jump from node to node

  4) faster than an unmyelinated axon, where depolarisation has to occur across entire axon
• Factors impacting speed of action potential

  1. myelination

  2) axon diameter

  3) temperature