In which of the following would the rate of impulse conduction be the greatest ?
ID: 95504 • Letter: I
Question
In which of the following would the rate of impulse conduction be the greatest?
a. a myelinated fiber of 10-µm diameter
b. a nonmyelinated fiber of 10-µm diameter
c. a nonmyelinated fiber of 20-µm diameter
d. a myelinated fiber of 1-µm diameter
e. the same in all because of the all-or-none principle
a. a myelinated fiber of 10-µm diameter
b. a nonmyelinated fiber of 10-µm diameter
c. a nonmyelinated fiber of 20-µm diameter
d. a myelinated fiber of 1-µm diameter
e. the same in all because of the all-or-none principle
Explanation / Answer
Answer: a. a myelinated fiber of 10-µm diameter (As explained below)
Diameter of a fiber and myelination are two factors that determine the rate of impulse conduction in a nerve. Thicker and myelinated fibers conduct impulses faster than thinner and non-myelinated fibers.
Myelinated neurons have areas of non-myelination called nodes of Ranvier. Action potentials occur along these nodes only. Therefore, the impulses need to jump over the areas of myelin from node to node. This type of conduction is called saltatory conduction (saltatory meaning jumping). And because the impulse jumps, it requires less time than an impulse along a non-myelinated neuron. Also, the fact that myelinated axons are insulated to the cell and thus have less resistance helps in conducting the impulse easily and rapidly.