nerve impulses

• What is the state of the neurone membrane at resting potential?

  It is polarised
• What happens when a stimulus is applied to a neurone?

  Sodium ion channels open
• What effect does sodium ion influx have on the axon?

  It makes the inside less negative
• What occurs if the threshold potential is reached?

  More sodium ion channels open
• What is the result of further sodium influx during depolarisation?

  It depolarises the membrane
• What happens during repolarisation of the membrane?

  Sodium ion channels close and potassium channels open
• What effect does potassium flow have on the axon during repolarisation?

  It makes the inside more negative
• What occurs after an excess of potassium flows out of the axon?

  It hyperpolarises the membrane
• What is the role of ion pumps during the refractory period?

  They restore the membrane potential
• What are the stages of the action potential?

  1. Resting potential: neurone membrane is polarised
  2. Stimulus and depolarisation:

  • Sodium ion channels open
  • Sodium influx makes inside less negative
  • If threshold is reached, more sodium channels open

  1. Repolarisation and hyperpolarisation:

  • Sodium channels close, potassium channels open
  • Potassium flows out, making inside more negative
  • Excess potassium causes hyperpolarisation

  1. Refractory period: ion pumps restore resting potential
• 3 factors effecting the speed of conductance of action potentials

  • myelination - the presence of Schwann cells causes the AP to jump to the next node of ranvier (saltatory conductance) which conserves energy for the axon
  • temperature - low temp = low speed due to low kinetic energy effecting facilitated diffusion involved in ion exchange
  • diameter of axon - large diameter = faster rate due to the lower SA:VOL ratio, meaning there is less ion leakage so axon recovers quicker after refractory period

   
• • The refractory period is a period of time to allow the axon to 'recover'