These questions are based from an online simulation of action potentials. 1) Why

Question

These questions are based from an online simulation of action potentials.

1)Why is so much more stimulus current needed to depolarize the squid axon than the membrane patch (.0001cm^2).

2)The spatial extent of the action potential is quite large. Explain why in terms of conduction velocity, and how it would change as a function of axon diameter.

3)The leakage potential of a cell is set to -20mV, and the stimulus current to 0 nA. Hypothetically, If a neuron or other excitable cell had this property, how would it behave? What biological function might it perform – can you think of an example of such a cell?

Explanation / Answer

1) The resting membrane potential of squid axon is -60 mV. The axonal membrane is also less permeable to sodium and potassium ions when compared to the membrane patch. Also, the Vm (resting membrane potential) is different from the Nernst potential of both sodium (+66 mV) and potassium (-84 mV). So, it requires more stimulus current to get depolarised.

2) The conduction velocity is inversely proportional to the square of the radius of the axon. So, when diameter is increased by two times, the velocity will increase by four times.

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