The period of time during which a second action potential cannot be initiated, no matter how large the applied stimulus is the absolute refractory period. Which statement is true for this period?

1. Potassium channels are open and the membrane is hyperpolarized
2. It immediately follows the relative refractory period
3. It allows an action potential to proceed in two directions along the length of an axon
4. It occurs when the sodium channels are open

A local anesthetic is a medication that causes reversible absence of pain sensation. They:
1. block the closure of voltage regulated potassium ion channels
2. stimulate the opening of voltage regulated potassium ion channels
3. block the opening of the voltage regulated sodium ion channels
4. stimulate the opening of voltage regulated sodium ion channels

Assertion: Nerve gas Sarin and agricultural insecticide Parathion can cause severe spastic paralysis in humans.
Reason: Sarin and Parathion act as inhibitors of the enzyme choline acetyl transferase.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.