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Ch. 11 Fundamentals of the Nervous System and Nervous Tissue
Marieb - Human Anatomy & Physiology 7th Edition
Marieb, Hoehn7th EditionHuman Anatomy & PhysiologyISBN: 9780805359091Not the one you use?Change textbook
All textbooksMarieb, Hoehn 7th EditionCh. 11 Fundamentals of the Nervous System and Nervous TissueProblem 14
Chapter 11, Problem 14

The velocity of nerve impulse conduction is greatest in
a. Heavily myelinated, large-diameter fibers
b. Myelinated, small-diameter fibers
c. Nonmyelinated, small-diameter fibers
d. Nonmyelinated, large-diameter fibers

Verified step by step guidance
1
Understand that the velocity of nerve impulse conduction depends primarily on two factors: the diameter of the nerve fiber and whether it is myelinated or not.
Recall that myelination increases conduction velocity by allowing saltatory conduction, where the impulse jumps between nodes of Ranvier, speeding up transmission.
Recognize that larger diameter fibers have less internal resistance to the flow of ions, which also increases conduction velocity.
Compare the options: heavily myelinated large-diameter fibers combine both factors that increase velocity, while nonmyelinated or small-diameter fibers conduct impulses more slowly.
Conclude that the greatest velocity of nerve impulse conduction occurs in heavily myelinated, large-diameter fibers.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Myelination and Its Effect on Nerve Conduction

Myelination involves the wrapping of axons with a fatty sheath called myelin, which acts as an insulator. This sheath enables saltatory conduction, where nerve impulses jump between nodes of Ranvier, significantly increasing conduction velocity compared to nonmyelinated fibers.
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Axon Diameter and Conduction Velocity

Larger diameter axons have lower internal resistance to the flow of ions, allowing faster propagation of electrical signals. Therefore, nerve fibers with greater diameter conduct impulses more rapidly than smaller ones.
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Types of Nerve Fibers and Their Conduction Speeds

Nerve fibers vary by diameter and myelination, affecting speed. Heavily myelinated, large-diameter fibers conduct impulses fastest, while nonmyelinated, small-diameter fibers conduct slowest. This classification explains differences in sensory and motor signal transmission.
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Related Practice
Textbook Question

During a neurobiology lecture, a professor repeatedly refers to group A and group B fibers, absolute refractory period, and myelin sheath gaps. Define these terms.

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Textbook Question

a. Describe the composition and function of the cell body.

b. How are axons and dendrites alike? In what ways (structurally and functionally) do they differ?

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Textbook Question

a. What is myelin?

b. How does the myelination process differ in the CNS and PNS?

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Textbook Question

a. Contrast unipolar, bipolar, and multipolar neurons structurally.

b. Indicate where each is most likely to be found.

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Textbook Question

What is the polarized membrane state? How is it maintained? (Note the relative roles of both passive and active mechanisms.)

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Textbook Question

Since all APs generated by a given nerve fiber have the same magnitude, how does the CNS 'know' whether a stimulus is strong or weak?

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