Answer
1.The ionic basis of nerve action potential
Depolarization
When depolarizing stimuli reach threshold level, voltage gated Na+ channels open and Na + influx into cell. This influx of Na + into cell result opening of more and more voltage gated Na+ channels (positive feedback mechanism). Therefore Na+ ion accumulate inside the nerve cell and membrane potential become positive.
Repolarization
In this stage voltage, voltage gated Na+ channels close and voltage gated K+ channels open and K efflux. This opening is slower and more prolonged than the opening of the Na
+ channels. The cell membrane repolarize due to efflux of K + ion .
After-hyperpolarization
The K+ channels close slowly it result after-hyperpolarization followed by a return to the resting membrane potential
2. All-or-non law
Minimal intensity of stimuli that need to produce action potential called threshold intensity . If given stimuli intensity enough to reach or above the level of threshold intensity ,action potential is produced .Further increment of intensity of stimuli produce no change of action potential .If the intensity of stimuli is below the level of threshold intensity ,action potential is not produced
3. How transmission along a myelinated nerve fiber is about 50 tims faster than along an unmyelinated nerve fiber
Transmission of action potential along nonmyelinated nerve fiber
At rest ( RMP ) inside the nerve membrane more negative ions are situated and more positive ions situated out side the membrane ( polarized membrane )
During action potential , Na + influx into cell and inside become positive and out side become negative ( depolarized membrane )
During propagation of action potential current flow from depolarized areas of the membrane to the adjacent resting membrane . This result depolarization of adjacent membrane and process travel along the entire length of the fiber .
Transmission of action potential along myelinated nerve fiber