OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is the purpose of the myelin sheath surrounding some axons?

1. To protect the neuron from damage

2. To slow down the electrical impulses

3. To act as an electrical insulator and speed up impulses

4. To allow for better connection between dendrites

The correct answer is: To act as an electrical insulator and speed up impulses

The myelin sheath serves as an essential insulating layer that wraps around the axons of many neurons. Its primary function is to act as an electrical insulator, which is crucial for the efficient transmission of electrical signals along the axon. By insulating the axon, the myelin sheath enables the electrical impulses, or action potentials, to travel more quickly and efficiently. This is because the myelin sheath facilitates a process known as saltatory conduction, where the electrical signals jump from one node of Ranvier, which are small gaps in the myelin sheath, to the next. This jumping mechanism significantly increases the speed of signal transmission compared to unmyelinated axons, where the impulse must propagate continuously along the membrane. This role in speeding up impulses is vital for the rapid coordination of responses in the nervous system. In contrast, options related to protection from damage or slowing down electrical impulses do not accurately reflect the primary function of the myelin sheath, while functioning as a means of improving connections between dendrites does not pertain to myelin's role at all.