5.1.3. Neuronal communication

• 1. changes in concentration of Ca2+ ions in the presynaptic neurone cause an action potential in the post synaptic neurone s the concentration is proportional to the strength of the stimulus
  2. Ca2+ changes from low to med/high cause i create in membrane potential
  3. action potential in the presynaptic neurone leads to opening of Ca2+ channels, allowing them to enter
  4. these cause the release of a neurotranmitter
  5. this causes Na+ ion channels to open in the post synaptic neurone
  6. if threshold is exceeded this causes an action potential in the post synaptic neurone, depolarising its membrane
• myelination effects the speed of conduction

  • depolarisation must occur across the whole membrane of the axon if not present
  • formed by schwann cells, cause depolarisation and action potentials to not occur as it stops the diffusion of Na+ and K+ ions
  • AP only occurs at nodes of Ranvier causing it to jump from one node to the next, known as saltatory condiction. allows impulse to travel much faster
  • local circuits of current that trigger depolarisation only exist between the nodes
• Diameter

  • neurones with thicker axons means that the impulse will be conducted at a higher speed as the membrane has a greater surface area so the ions can diffuse across
  • also possess a greater volume of cytoplasm containing ions. this reduces electrical resistance so that an action potential can push into the next section faster
• temperature

  • ectotherms means colder conditions can slow down the conduction of nerve impulses
  • less kinetic energy available for facilitated diffusion during an action potential