Which of the following statements is correct?

A) Myelin sheaths form an insulating layer around the axons of neurons in the central and peripheral nervous systems. These structures function to slow the transmission of impulses along the axon.
B) Myelin sheaths form an insulating layer around the axons of neurons in the central and peripheral nervous systems. These structures function to speed up the transmission of impulses along the axon.
C) Myelin sheaths form an insulating layer around the axons of neurons only in the peripheral nervous system. These structures function to speed up the transmission of impulses along the axon.
D) Myelin sheaths form an insulating layer around the cell bodies of neurons in the central and peripheral nervous systems. These structures function to speed up the transmission of impulses along the axon.