A minimum rate of change in membrane potential is required to initiate the spike. If the membrane potential is changed very slowly, the critical firing level (THRESHOLD) can be passed without an action potential being initiated. During any maintained hypopolarization (i.e. SLOWLY INCREASING SUBTHRESHOLD STIMULUS) that does not cause a spike to occur, the critical firing level becomes more positive. This phenomenon is called accommodation. When the hypopolarization is terminated, both the membrane potential and the critical firing level return to their original values. If, however, the minimum rate of change of membrane potential is exceeded, the spike will be initiated as the membrane potential becomes more positive than the critical firing level.
Posted on: Wed, 28 May 2014 04:45:59 +0000
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