The nerve impulse

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  • Inactive neuron
    • Positive ions int he fluid outside
    • negative ions inside (-70mv) - this inactive charge is called resting potential
      • When charge reaches -50mv, neuron reaches its threshold and nerve impulse is triggered
        • nerve impulse is an all or nothing event
      • During this nerve impulse or action potential, the axon membrane is pierced by tiny holes called ion channels
      • The molecules blocking these tiny openings pop open and allow Na+  to rush into the axon (the channels open near soma first and then down the length of the axon)
      • After the action potential passes, there is a negative after potential state as K+ flow out of the axon to quickly restore its negative charge
    • Ultra-small electrodes places inside and outside an axon measure its activity
    • Saltatory conduction can occur instead of normal nerve impulse
      • Axons of some neurons are coated with a fatty layer called myelin; small gaps in myeling help nerve impulses move faster by leaping from gap to gap
        • If the myelin is damanged: numbness, weakness or paralysis eg - multiple sclerosis


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