lecture 8

• Neuron


  Electrochemical activity

  
• Contents


  • Resting potential
  • Action potential
  • Signal & channel disruption
  • Synapse
  • Synaptic transmission
  • Postsynaptic potential
• Neurons


  • Axons about 100x larger than human axons
  • Fluids inside and outside contain ions (electrically charged particles)
  • More negative ions inside than outside when at rest (inactive/resting potential)

  
• Resting potential


  Electrical charge across the cell membrane in the absence of stimulation
• At resting potential, concentration of charged ions are: Sodium (Na⁺) and Chloride (Cl⁻) ions more outside, Potassium (K⁺) and large proteins (A⁻) more inside, Overall, inside of membrane at rest has a charge of -70 millivolts relative to extracellular side

  
• Resting potential


  There is a store of energy on the intracellular side relative to the extracellular side, Negative charge maintained by "leaking" Potassium out cell (diffusion)

  
• Action potential


  When the membrane reaches threshold, Na (sodium) channels open (depolarization), Allows Na into cell and raises voltage (+), Eventually, Na channels close and K ions can also flow in (repolarization)

  
• Action potential formation


  Sodium channels open sequentially along the axon (propagation), Triggers release of neurotransmitter
• Agents that block Na (sodium) channels


  • Local anaesthetics e.g. ketamine, propofol
  • Anticonvulsants, including oxcarbazepine
  • Antiarrhythmia drugs
  • Some neurotoxins e.g. tetrodotoxin from pufferfish
  • Research into cannabidiol's effects
• Synapse


  Where neurons meet to pass along signal, Presynaptic neuron = where signal is coming from, Postsynaptic neuron = receiving signal at receptor sites, Microscopic gap between them called synaptic cleft

  
• Synaptic transmission


  Electrical signals travel down neuron via action potential but can't jump the gap, Presynaptic neuron releases neurotransmitters into the synaptic cleft, Signal travels with the neurotransmitter, which fuses with receptor site of postsynaptic neuron

  
• Postsynaptic potential (PSP)


  Voltage change at receptor site, Probability that the postsynaptic neuron will fire, Positive voltage shift = excitatory PSP, Negative voltage shift = inhibitory PSP