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 1

myelin sheath

The axon of many neurons has an outer layer called a myelin sheath  see Figure above  . Myelin is a lipid produced by a type of a glial cell known as a Schwann cell. The myelin sheath acts like a layer of insulation, similar to the plastic that encases an electrical cord. Regularly spaced nodes, or gaps, in the myelin sheath allow nerve impulses to skip along the axon very rapidly.