Final answer:
The myelin sheath is not a function of neurons. Its main function is to insulate and protect the axons of neurons, allowing for faster transmission of electrical signals.
Step-by-step explanation:
Out of the given options, forming the myelin sheath is NOT a function of neurons. The myelin sheath is formed by specialized cells called oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). Its main function is to insulate and protect the axons of neurons, allowing for faster transmission of electrical signals.