Q22 - Although severing a motor nerve kills

[Laura Damone]

Question Type:
Most Strongly Supported

Stimulus Breakdown:
No argument here, so we just need the facts. Nerves can regenerate at the rate of about 1 mm per day. Growing nerve cells need the original nerve sheath. The sheath starts to disintegrate after about three months if there isn't living nerve tissue within it.

Answer Anticipation:
Most Strongly Supported questions are notoriously hard to prephrase. Keep an eye on the conditional statement "that sheath begins to disintegrate after about three months unless there is living nerve tissue within it." MSS questions will often hinge on just one piece of the stimulus, and this is the piece that seems most likely to bear fruit.

Correct answer:
D

Answer choice analysis:
(A) A directly proportional relationship like A describes is pretty hard to prove, so that's one strike against A. Furthermore, in cases where the nerve is severed close to the muscle it controls, doubling the speed at which the new nerve cells grow might not drastically increase the likelihood of the regrowth reaching its target. Maybe it's so likely already that the likelihood can't be doubled.

(B) The last line talks about nerve sheath disintegration, but it only says that the process begins in the absence of living nerve tissue. It doesn't say anything about reversing or slowing the process once it's begun.

(C) The "cannot" in this answer has too strong a degree. Is it less likely that functionality can be restored after 3 months? Well, it's less likely to be restored by regeneration. But is it impossible to restore it? We don't know. Maybe there are other ways to restore functionality without natural nerve regrowth.

(D) Here it is! Now, some folks might have eliminated this one because the idea of implanting nerve tissue isn't discussed in this stimulus. While that's true, it's still a concept within the scope of this conversation, since we're told the nerve sheath starts to disintegrate in the absence of living nerve tissue within it. So, in theory, a successful implantation of live tissue to the sheath would increase the likelihood of nerve regeneration in some cases. Is this 100% guaranteed? Nope. It wouldn't be a right answer if this were a Must Be True question. But is it close enough for a Most Strongly Supported question? You bet.

(E) Surgical intervention? Where'd that come from? We don't have any info about surgical intervention. For all we know, this nerve regeneration happens totally on its own, in which case this answer is contradicted, not supported!

Takeaway/Pattern:
No prephrase? No problem! Don't force it on Most Strongly Supported questions. Know the stimulus, and knock out answers that are hard to prove because they deal with proportional relationships (A) or have an extreme degree (C).

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