nerve impulses

• describe resting potential

  when a receptor is not stimulated, there's a difference in electrical charge between the outside and inside of a neuron

  • -70mV more positive ions on the outside compared to the inside
• how is resting potential maintained

  • higher conc of Na+ ions in the neuron and high conc of K+ ions out of the neuron
  • membrane is more permeable to K+
  • using a sodium-potassium pump, it creates an electrochemical gradient causing 3 K+ ions to diffuse in and 2 Na+ to diffuse out via active transport
• stimulus: 

  excites the neurons cell membrane causing Na+ ion channels to open allowing it to diffuse into the axon, membrane becomes less negative

  • if the neuron is stimulated enough to reach threshold (-55mV) results to action potential
• describe action potential (depolarisation)

  once threshold is reached, more voltage-gated Na+ ions channels open allowing Na+ ions to diffuse in

  potential difference increases as its more positive inside than outside the cell
• repolarisation

  at around +30/40 mV, Na+ ion channels close and K+ ion channels open, the membrane is more permeable to K+ ions so they diffuse out of the cell
• hyperpolarisation

  potential difference become even more negative as there's an ‘overshoot’ as too many K+ ions diffuse out
• refractory period:

  time delay

  • to make sure action potentials do not overlap and pass as discrete impulses
  • to ensure action potentials travel in one direction
  • limits the no. of impulse transmission
• all or nothing principle:

  if depolarisation does not exceed -55mV, an action potential won't be established. 
• factors affecting conduction:

  myelination and saltatory conduction,axon diameter; temperature
• myelination:

  action potentials jumps from node to node (saltatory conduction) which means it travels faster as it doesn't have to travel the entire length of the axon
• temperature

  at a higher temperature, ions diffuse faster so speed of conductance increases until 40 degrees as protein channels begin to denature
• axon diameter

  larger diameters means that there's less resistance to the flow of ions in the cytoplasm. faster the speed of conductance