Nervous Coordination

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  • Nervous Coordination
    • Nerve Impulses
      • Neurones
        • Structure
          • Adapted to carry rapid nerve impulses
          • Shwann Cells
            • wraparound axons
          • Cell body
          • Dendrites - carry nerve impulses towards cell body
          • Axon - single fibre that carries impulses away from cell body
            • axons can be myelinated
              • Myelin sheath and nodes of ranvier between
      • Action Potential
        • Stimulus opens voltage - gated sodium channels
          • Influx of sodium ions cause depolarisation of axon which reaches a threshold
            • Action poential - wave of depolarisation
              • at +40mV, sodium channels close and potassium channels open
                • Repolarisation
                  • hyperpolarisation - tempory overshoot of outward potassium ions
                    • Sodium -potassium channel returns membrane potential to -65mV
                      • Refractory Period
                        • Discrete impulses
                        • Limits of number of impulses
                        • unidirectionality
            • All-or-nothing response
      • Resting Membrane potential
        • around  -65mV, in a polarised state
        • Sodium potassium pump in axon membrane
          • 3 sodium ions out, 2 potassium ions in
        • Protein chnalles allow ions to diffuse in and out
          • Membrane is more permeable to k+ ions, so some K+ ions diffuse back out
    • Synaptic Transmission
      • Synapse
        • unidirectionality
          • always from presynaptic neurone to postsynaptic neurone
        • inhibitory synapses
          • chloride ions enter postsynaptic neurone
            • hyperpolarisation
        • junction between 2 neurones
        • neuromuscular junction - between motor neurone and muscle end plate

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