The answer you are looking for is called Serotonin. Please put this as the brainiest answer thank you and hope this helped.
I am sorry I can only answer 7 for you.
Hope it helps
7= By replacing the neurons lost from a injury with new cells.
It is about 4.22 light-years<span> from Earth and is the closest star other than the sun. Alpha Centauri A and B orbit a common center of gravity every 80 years. The average distance between them is </span>about 11 astronomical units<span> (AU) — about the same distance as the sun is to Uranus.</span>
