junctions

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  • nerve and muscle junctions
    • nerve junctions
      • action potential arrives presynaptic knob.
        • voltage gated Ca2 channels open, ions diffuse into knob
          • Ca2 ions cause synaptic vesicles fuse with presyn membrane
            • acetylcholine secreted exocytosis, diffuse across cleft
              • acetylcholine bind receptors on Na channels on postsyn membrane
                • Na channels open, Na ions through mebrane into neurone postsyn
                  • if suffi cient generator potential combine, threshold potential across membrane reached
    • acetycholinesterase
      • hydrolises acetylcholine
        • choline + ethanoic acid
          • re enter presyn knob diffusion, atp re combines
    • Muscular junctions
      • impulse arriives neuro muscular junction. vesicles fuse presyn knob
        • acetylcholine diffuse into gap
          • acetylcholine binds receptors on sarcolemma, depolarisation
            • depolarisation waves travel down t-system
              • t-system depolarisation Ca2 release from sarcoplasmic reticulum
                • Ca2 binds proteins in muscles causes contraction

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