Asecond nerve impulse cannot be generated until a. the na ions have been pumped back into the cell b. the membrane potential has been reestablished c. proteins have been resynthesized d. all sodium gates are closed

(B). the membrane potential has been reestablished

Explanation:

Nerve impulse can be defined as a signal that transmits along the nerve fibers. The neurons are said to be in resting phase when there is no nerve impulse.

When a stimulus is applied to resting membrane, sodium ions freely pass inside the cell and membrane is now said to be in depolarized phase. Due to this, a difference in electrical potential is generated across the membrane, known as nerve impulse or action potential.

When the action potential is over (after transmitting the nerve impulse through neuron) the cell membrane potential returns back by repolarizing the membrane.

Once the membrane potential is completely returned to its  resting potential (when membrane potential is reestablished), the neurons become ready for second or next nerve stimulus.

Thus, the correct answer is option (B).

the fossil record provides evidence of a common ancestor to many species.

acceleration = 18/3 = 6 m/s per second.

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-lavira: )