PrepTest 125, Section 3, Question 21
Neurobiologists once believed that the workings of the(446 more words not shown)
Which one of the following(11 more words not shown)
- AEvidence shows that(33 more words not shown)
- BEvidence shows that(31 more words not shown)
- CEvidence shows that(27 more words not shown)
- DEvidence shows that(29 more words not shown)
- EEvidence shows that(35 more words not shown)
Reading the passage
We've already predicted an explanation of chemical signaling and the possibility of targeted treatments. That doesn't mean the brain has stopped using electricity. The first paragraph still has ions generating an electrical impulse inside the receiving neuron.
What we’re looking for
Several choices look very similar, so keep that distinction in view as we compare them.
Working the answers
- A
The treatment part fits, but the opening goes too far. The workings of the brain aren't guided by chemicals instead of electrical signals. Both have roles. What changes is the explanation of how a signal passes between neurons.
- B
It makes the same broad mistake about excluding electrical signals. It also says the chemicals form the family, when the third paragraph groups the receptors.
- C
Its opening correctly describes transmission between neurons. But again, the family consists of receptors, not the chemicals. It also leaves out the final paragraph's medical significance.
- DCorrect
“Between neurons” is the crucial limit. Chemical binding triggers the ion movement that generates an electrical impulse in the receiving cell; the theory isn't that all brain activity is chemical rather than electrical. The second half then captures how differences among receptors may permit selective treatment. This is a more precise version of our prediction.
- E
This concentrates on the final discovery about receptor differences. It leaves out most of the account: the chemical-transmission theory, the obstacle to understanding it, and the evidence explaining its mechanism. It also presents the treatment possibility more firmly than the writer does.
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