The white lipid covering of axons is called what?

• A. The grey matter of brain
• B. The protective membrane of neurons
• C. The white lipid covering of axons
• D. The synaptic vesicle

Answer: (C)

Myelin sheath provides insulation and speeds nerve signaling. This lipid-rich layer wraps around axons, created by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system. Its lipid content gives white matter its color and allows impulses to jump quickly from one node of Ranvier to the next through saltatory conduction, making transmission faster and more energy-efficient. The bare axon regions between myelin sheaths (the nodes) host many ion channels to re-energize the signal as it travels. In contrast, the protective membrane of a neuron refers to the plasma membrane of the cell, and a synaptic vesicle is a small vesicle at the synapse carrying neurotransmitters. The gray matter of the brain describes regions rich in neuron cell bodies, which are not myelinated to the same extent.