in Neural Control and Coordination (Nervous System) by

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Resting Potential:

  1. The nerve cells bathed in a fluid called interstitial fluid.  In this, fluid remains dissolved sodium (Na+) and potassium (K+) ions.
  2. During the resting phase, the neurilemma is comparatively 30 times more permeable to potassium ions than to sodium ions.
  3. As a result sodium ions are present in high concentration outside the membrane and in low concentration on the inner side.
  4. Thus outer surface shows positive electric charge and inner surface shows negative charge due to organic anions.
  5. The membrane at this stage is said to be in polarized state and the resting potential remains at a value of 80 mV.

Action Potential:

  1. When a stimulus of any kind is applied to the nerve, it disturbs the set up.  There is marked change in the potential, it is called action potential.
  2. The polarity of membrane gets reversed after excitation because the sodium ions move inward and potassium move outward.  Thus membrane is said to be depolarized.
  3. It is termed active phase during which the inner surface is positively charged and outer surface negatively charged.
  4. Typically it takes much simultaneous graded electric potential to initiate an action potential.
  5. An action potential is initiated each time the membrane potential is raised to threshold potential.  Because action potentials never occur below the potential upon the occurring always the same size, action potentials are called all or none events.
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