Bio- Neurones

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  • Neurones
    • Types of Neurones
      • Sensory
        • Carry action potential from sensory receptor to CNS
        • -Long dendron-short axon
      • Motor
        • Carry action potential from CNS to effector
    • All neurones have...
      • Gated ion channels
      • Na+/K+ ion pumps
        • 3Na+ out to 2K+ in
      • A p.d. across membrane
      • a myelin sheath
    • Resting State
      • ATP used to pump 3Na+ out to every 2K+ in
      • Membrane-> more permeable to K+ than to Na+ so many diffuse in
      • Cell cytoplasm-> contains large anions
      • Membrane is polarised
      • -60mV
    • Action Potential
      • Resting state-> polarised -60mV
        • Na+ channel, some Na+ diffuse in
          • Membrane deploarises- reaches threshold potential
            • -50mV
            • Voltage-gated Na+ channels open- Na+ flood in
              • Membrane reaches action potential
                • +40mV
                • Na+ channels close/ K+ channels open
                  • K+ diffuse out- membrane repolarises
                    • P.d. overshoots-    hyperpolarised
                      • Cell returns to resting state
    • Refractory Period
      • Short period of time afterfiring where it is more difficult to stimulate a neurone
        • Absolute
          • 2nd stimulus won't cause another action potential
        • Relative
          • 2nd action potential can occur but only if stimulus is considerably higher than threshold potential
        • Reasons...
          • Restore original polarity
          • Ensures action potentials are only transmitted in one direction


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