3. Sea vegetables. Sea vegetables are rich in iodine. Iodine attaches to tyrosine (an amino acid) to form thyroxine. If you have insufficient levels of iodine, it becomes a rate-limiting step in the production of thyroid hormones and you'll inhibit your thyroid function.
Confidence votes 48. Special glia called Schwann cells form the myelin sheath which cover axons in the peripheral nervous system. The myelin sheath is actually two layers. The first layer surrounding the axon is called the myelin sheath and it is made up of the plasma membrane of the Schwann cells. The Schwann cells cytoplasm creates the second layer and is called the neurolemma. A neuron in the peripheral nervous system with a myelin sheath is called a myelinated neuron.
Schwann cells are the cellular counterparts to oligodendrocytes in the peripheral nervous system. Similarly to oligodendrocytes they form the myelin sheath. In contrast to the oligodendrocyte each Schwann cell is associated with only one axonal segment. While the myelin structure formed by oligodendrocytes and Schwann cells has a similar ultrastructure, it is not composed of an identical set of proteins.