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Nervous system 2 (Change in membrane potential over time (At rest a nerve…

- - - - To return the nerve to resting potential repolarization occurs at point D due to K ions moving out of the cell down there conc gradient.
      - Point E shows Hyperpolarization which is caused by K ions leaving the cell. Over a short time the potential returns to resting and this whole process occurs over a matter of mS.
- - - - Achieved through frequency of impulses
      - Code for stimulus strength is 'frequency modulated'
      - As intensity of stimulation increases more axons will become activated - this process is called recruitment
- - - - interval during which a second AP cannot be initiated no matter how large a stimulus is applied
      - Caused by inactivation of Na+ channels that originally opened during membrane depolarisation
      - Channels remain inactivated until membrane repolarises
    - - Interval during which initiation of second signal is inhibited but not impossible
      - Immediately follows absolute
      - As voltage gated K channels open to terminate AP by repolarising membrane K ions flooding out of cell bring membrane further away from threshold
        
        this causes hyperpolarisation until K levels reach resting
- - - - Myelin increases speed of conduction
      - Without myelin wouldn't be able to run etc
    - - Some invertebrates such as giant squid have giant unmyelinated axon that transmit signals rapidly