Question

layer of insulation on axons of certain neurons that helps speed nerve impulse transmission
muscle cell
muscle fiber
schwann - cell
myelin sheath
hair cell

Explanation:

The myelin sheath is a layer of insulation on axons of certain neurons. It forms a fatty covering that allows nerve impulses to travel more quickly along the axon through saltatory conduction. Muscle - cell and muscle - fiber are related to muscle tissue, not nerve insulation. Schwann cells are the cells that produce myelin in the peripheral nervous system, but the actual insulation layer is the myelin sheath. Hair cells are related to sensory reception in the ear and other sensory organs, not nerve impulse transmission insulation.

Answer:

myelin sheath