Final answer:
Myelin is a lipid-rich substance that surrounds axons of neurons and helps speed up electrical signal transmission by keeping ions inside the axon.
Step-by-step explanation:
Myelin is a lipid-rich insulating substance that surrounds the axons of many neurons. It helps keep ions inside the axon, which speeds up the transmission of electrical signals. The insulation provided by myelin prevents signals from jumping between adjacent nerves, allowing the electrical signal to travel faster along the axon.