action potential

• What is an action potential

  change in membrane potential - propagates along axon of neurones

  • robust
  • rapid
  • orthodromic
  • all or nothing
• Recording AP

  extracellular electrophysiology

  • electrode outside cell
  • stimulating electrode the record electrode at other end of the nerve
  • AP picked up
• Compound action potential (CAP)

  sum of action potentials from all axons simultaneously contributing to signal
• Graded potentials (PSPs)

  small changes in membrane potential - sit below threshold for AP

  can be depolarised (EPSP) - make more positive - more likely to make AP

  OR hyperpolarising (IPSP) - make more negative - less likely for AP
• summation of graded potentials

  determines if AP is generated

  SPATIAL:

  • multiple inputs to one neurone at the same time - added together

  TEMPORAL:

  • one input sending multiple action potentials very quickly one after the other
• Voltage Clamp

  Records movement if ions during AP

  can control potential difference across cells and records current

  
• voltage gated ion channels

  open and close in response to voltage

  • Loss of function
  • Don’t fire action potentials
  • Reduced transfer of information
  • E.g. loss of sensations
  • Gain of function
  • Over fire action potentials
  • Excess transfer of information
  • E.g. increased sensitivity to sensations