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.
n. The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and facilitates the transmission of nerve impulses. In the peripheral nervous system, the sheath is formed from the membrane of the Schwann cell, and in the central nervous system it is formed from oligodendrocytes. Also called medullary sheath.