What is the purpose of the respiratory system in the body?
A. provides energy for the body
B. filters air and brings oxygen into the body
C. circulates oxygen to tissues in the body
D. provides structure for the body and protects
important organs

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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some of your causes might be acidic rain or natural wildfires that cause the parks to be degraded

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