Watch these recommended TED-Ed Lessons:
What happens when you have a concussion?
Each year in the United States, players of sports and recreational activities receive between 2.5 and 4 million concussions. How dangerous are all those concussions? The answer is complicated and lies in how the brain responds when something strikes it. Clifford Robbins explains the science behind concussions.

Could your brain repair itself?
Imagine the brain could reboot, updating its damaged cells with new, improved units. That may sound like science fiction — but it’s a potential reality scientists are investigating right now. Ralitsa Petrova details the science behind neurogenesis and explains how we might harness it to reverse diseases like Alzheimer’s and Parkinson’s.

How do animals experience pain?
Humans know the surprising prick of a needle, the searing pain of a stubbed toe, and the throbbing of a toothache. We can identify many types of pain and have multiple ways of treating it — but what about other species? How do the animals all around us experience pain? Robyn J. Crook examines pain in both vertebrate and invertebrate animals.

Why don’t poisonous animals poison themselves?
Thousands of animal species use toxic chemicals to defend themselves from predators. Snakes have blood clotting compounds in their fangs, the bombardier beetle has corrosive liquid in its abdomen and jellyfish have venomous, harpoon-like structures in their tentacles. But how do these animals survive their own poisons? Rebecca D. Tarvin details the strategies that protect animals from themselves.

Why do animals have such different lifespans?
For the microscopic lab worm C. elegans, life equates to just a few short weeks on Earth. The bowhead whale, on the other hand, can live over two hundred years. Why are these lifespans so different? And what does it really mean to ‘age' anyway? Joao Pedro de Magalhaes explains why the pace of aging varies greatly across animals.