OSMT (Ontario Society of Medical Technologists) Practice Exam

Neurons are electrically insulated by the presence of the:

1. a. White matter

2. b. Myelin sheath

3. c. Astrocytes

4. d. Interneuron

The correct answer is: b. Myelin sheath

The presence of the myelin sheath is crucial for the electrical insulation of neurons. Myelin, a fatty substance produced by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system, wraps around the axons of many neurons. This insulation enhances the speed of electrical impulses (action potentials) by allowing them to jump between the nodes of Ranvier—a process known as saltatory conduction. The myelin sheath thus not only improves the efficiency of neural communication but also protects the axon from potential damage and interference from surrounding electrical signals. The other options refer to different components or types of cells in the nervous system. White matter consists of myelinated axons, but it does not perform the insulating function itself. Astrocytes are a type of glial cell that support and maintain the environment for neurons, but they do not insulate axons. Interneurons serve a specific role in processing information within the central nervous system and are not directly involved in insulation. Hence, the myelin sheath is the correct and primary structure responsible for electrically insulating neurons.