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Q3.    Explain the following processes:

         (a) Polarisation of the membrane of a nerve fibre

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Polarisation of the membrane of a nerve fibre:

  • When the nerve fibre is at the resting phase, it is said to be in the polarised state.
  • In a polarised state, the membrane of the nerve fibre experiences resting potential.
  • The following steps take place during the process of polarisation of the membrane of a nerve fibre:
    • When a depolarised region of a nerve fibre starts becoming polarised initially, there are more K+ ions outside the nerve fibre and the axon membrane contains large amount of Na+ ions.
    • As the region of the membrane starts attaining the polarised state, the membrane becomes more permeable to K+ ions and impermeable to Na+ ions and negatively charged proteins.
    • 3 Na+ ions are sent outside the axon and 2 K+ ions are sent into the axon by a sodium-potassium pump by active transport.
    • The inner side of the membrane becomes electronegative (negatively charged) and the outer side becomes electropositive (positively charged) because of the movement of sodium and potassium ions. This makes the nerve fibre polarised.
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Priyanka Kumari

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