instruction:
Given a scientific question, generate a correct answer to it.
question:
What is the outer layer of an axon that acts like a layer of insulation, similar to the plastic that encases an electrical cord?
answer:
myelin sheath

question:
Urea and carbon dioxide are molecules with how many carbon atoms?
answer:
one

question:
What was first discovered in songbirds that produce new neurons while learning songs?
answer:
neurogenesis