Here's a breakdown:

* Myelin sheath: This is a fatty, insulating layer that wraps around the axon. It's formed by specialized cells called Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system.

* Function of the myelin sheath: It acts like insulation on an electrical wire, speeding up the transmission of nerve impulses (action potentials) along the axon.

In addition to the myelin sheath, the axon is also surrounded by other structures:

* Axon membrane: This is the cell membrane that encloses the axon and regulates the movement of ions, which are essential for nerve impulse transmission.

* Axoplasm: This is the cytoplasm within the axon, containing the organelles and other structures needed for the axon's function.

* Neurolemma: This is the outermost layer of the Schwann cell, which wraps around the myelin sheath.

Let me know if you'd like to know more about any of these structures!