Neurones - action potential and resting potential

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  • Neurones
    • Resting potential
      • -70 mV
        • Inside of the axon is more negative than the outside
          • Membrane is polarised
          • 1
            • Na+/K+ pump creates a conc. gradient across the membrane by pumping out Na+ ions and pumping in K+ ions
              • Leads to a high conc. of Na+ outside of the axon and a high conc. of K+ inside the axon
                • Helps balance charge across the cell surface membrane
              • Pump is driven by energy supplied by the hydrolysis of ATP
          • 2
            • K+ diffuses out of the cell (down the K+ conc. gradient through a K+ channel protein) making the outside of the membrane positive and the inside negative
              • Membrane is permeable to K+ ions but impermeable to Na+ ions
          • 3
            • Electrical gradient pulls K+ back into the cell (through the K+ protein channel)
          • 4
            • at -70 mV the two gradients counteract each other and there's no net movement of K+
              • There's an electrochemical equilibrium for K+ and the membrane is polarised
    • Action potential
      • Caused by changes in the permeability of the cell surface membrane to Na+ and K+ due to the opening and closing of voltage dependent gated channels.
        • 3 Stages
          • 1
            • Depolarisation
              • Neurone is stimulated
                • Some depolarisation occurs
              • Na+ gate opens, some of the voltage dependent Na+ ion channels open
              • Sodium flows in
                • Depolarisation increases
              • More gates open
                • Causes further depolarisation
              • Example of positive feedback
                • change encourages further change
              • Can't control the degree of depolarisation
                • Action potential is either there or it's not
                  • All or nothing
              • Higher conc. of Na+ outside of the axon
                • Sodium ions flow rapidly into the axon
                  • Positive charge builds up
                    • Potential difference = +40 mV
              • Only occurs in the gaps between the myelin sheath (nodes of Ranvier)
          • 2
            • Repolarisation
              • Voltage-dependent Na+ channels close
                • Na+ permeability reverts to low
              • Voltage-dependent K+ channels open due to depolarisation
                • K+ moves out of axon
              • Inside of cell more negative than the outside
          • 3
            • Restoring the resting potential
              • Membrane highly permeable to K+ ions
                • Hyperpolarisation
                  • potential difference more negative than resting potential
              • Resting potential re-established by closing the K+ channels
                • K+ ions diffuse into the axon
              • Refractory period
                • 5 miliseconds
                • Time taken to restore the resting potential
    • Untitled

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