A myelinated neurone conducts impulses faster than an unmyelinated one because
- A. the impulse jumps from one node of Ranvier to the next
- B. myelin conducts electricity better than cytoplasm
- C. myelinated axons are always much thinner
- D. myelin increases the number of sodium channels along the whole axon
Explanation
Myelin is an insulator, so ions can cross the membrane only at the gaps between Schwann cells, and depolarisation therefore leaps from node to node in what is called saltatory conduction. This can raise conduction speed above 100 metres per second, against a few metres per second in an unmyelinated fibre of the same diameter. Loss of myelin in multiple sclerosis slows or blocks conduction.
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