sandra
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During a visit to the dentist’s office, a 17-year-old girl is given an injection of lidocaine in her mouth for a local procedure. Which of the following correctly demonstrates the order in which the nerve fibers are affected by lidocaine (from first to last)?
A. Large myelinated nerve fibers > large unmyelinated nerve fibers >
small myelinated nerve fibers > small unmyelinated nerve fibers
B. Large unmyelinated nerve fibers > small myelinated nerve fibers > large
unmyelinated nerve fibers > small unmyelinated nerve fibers
C. Large unmyelinated nerve fibers > small unmyelinated nerve fibers > large
myelinated nerve fibers > small myelinated nerve fibers
D. Small myelinated nerve fibers > large myelinated nerve fibers > small
unmyelinated nerve fibers > large myelinated nerve fibers
E. Small unmyelinated nerve fibers > small myelinated nerve fibers > large
unmyelinated nerve fibers > large myelinated nerve fibers
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| mediocre
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http://www.prep4usmle.com/forum/thread/42816
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| vallia
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E
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| klimt
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E
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| NE
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The early laboratory study supported "size principle" which meant that the sensitivity of nerves to local anesthetics was inversely proportional to axon diameter .These experiments suggested that large myelinated axons were substantially more susceptible to lidocaine than small unmyelinated axons. Fink and Cairns demonstrated that the concentration of lidocaine needed to block myelinated axons was smaller than that in unmyelinated axons. Jaffe and Rowe (4) reported that myelinated axons were significantly more susceptive to the conduction velocity slowing the effects of lidocaine than unmyelinated axons. In contrast, spinal and epidural administration of lidocaine produces differential nerve block in accordance with the size principle that the sensitivity of nerves to local anesthetics is inversely proportional to axon diameter.
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| NE
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so I guess it is A
http://www.anesthesia-analgesia.org/cgi/content/f...
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