Question

if the action potential is always the same in size and shape, why in the "giant squid's axon" experiment ,carried out by Hodgkin and Huxley, the peak of the action potential depends on the Na+ concentration in extracellular solution ?

Answer 1

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Answer 2

Normally extracellular Na is 142mEq/L and K is 4mEq/L
intracellular Na is mEq/L and K is 140mEq/L.
This intracellular Potassium is responsible for the intracellular negativity which is maintained around -90millivolts by the active Sodium-Potassium Pump. An Action Potential is associated with rapid changes in the membrane potential moving towards positivity and upon reaching a threshold shooting up to 40milliovolts.
This shooting up is facilitated by voltage gated sodium channel.
when the voltage is somewhere between -70 and -50 millivolts this gate opens permitting Na ions to pour into the cell. The time for which this gate is kept open is very limited . Immediately the gate closes and Repolarisation starts. Under such a situation the extracellular Na levels if low naturally cannot pour in to rise the action potential peak. Alternatively high levels of extracellular Na can make more Na move in within given gate time resulting in Higher action potential peak levels