Nervous System

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  • Nervous System
    • Resting Potential POLARISED
      • More -ive inside - 70mV lower
        • Maintained by Na/K Pumps = POLARISED
          • Na+/K+ Pump
          • 3Na+ out for every 2K+ In
            • Against conc grad
      • Active= +ive +40mV
      • Inactve= -ive -70mV
    • Action Potential DEPOLARISED
      • Na+ channels open
        • Inside becomes less positive
          • = Depolarised. +40mV potential diff
            • Na+ channels close
              • K+ channels open
                • K+ moves out
                  • positive charge inside removed
                  • Potential diff starts 2 return to norm = Repolarisated
      • If stimulus is strong and reaches threshold voltage gated channels open
        • Na+ channels open
          • Inside becomes less positive
            • = Depolarised. +40mV potential diff
              • Na+ channels close
                • K+ channels open
                  • K+ moves out
                    • positive charge inside removed
                    • Potential diff starts 2 return to norm = Repolarisated
        • If stimulus doesn't reach threshold = no depolarisation
    • Restoring Resting Potential
      • More K+ leaves than needed = Hyperpolarised
        • Refractory Period occurs
          • K+channels eventually close
          • Another Impulse cannot occur during this
          • Ensure impulse travels in 1D
    • All or Nth Law
      • Unless threshold reached by stimulus no action potential
      • Size of impulse independent of stimulus intensity
      • More Intense Stimulus = Greater Frequency of Action potentials
    • Factors affecting Transmission Speed
      • Axon Diameter
        • Wider axon = faster impulse
      • Myelin Sheath
        • Increases Speed of impulse
          • Impulse jumps node to node
        • Impulse jumps node to node
      • Temperature
    • Saltatory Conduction
      • Latin 'Saltare' - to leap

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