Reading Comprehension

PT125 · S3 · P4 · Q26 Neurotransmitter Theory

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Neurobiologists once believed that the workings of the brain were guided exclusively by electrical signals; according to this theory, communication between neurons (brain cells) is possible because electrical impulses travel from one neuron to the next by literally leaping across the synapses (gaps between neurons).

Topic

How neurons communicate: the shift from an electrical to a chemical understanding, and the medical implications of that shift.

Framework

Old / New

Main Point

Neuroscientists now understand that neurotransmitter-gated ion channels are key to how neurons communicate chemically—not just electrically—and this insight could lead to the development of targeted treatments for brain disorders. (Most valuable sentence: The last sentence of P2 and core ideas in P3 & P4 summarize both the breakthrough and its significance.)

P1: Shifting from Electrical to Chemical Communication

Early neuroscientists thought neurons talked only through electrical impulses “leaping” across synapses. Some, though, were skeptical and speculated that chemical signals (neurotransmitters) might be involved.

P2: Scientific Skepticism, Then New Evidence for Chemistry

Most scientists were slow to fully believe the chemical theory, partly because they didn't get how a chemical could let ions flow through a cell's surface. But recent evidence has shown that the structure of receptors is the key.

P3: How Neurotransmitter-Gated Ion Channels Work

We learn these receptors are like double-duty doors: one part binds the neurotransmitter, which causes the receptor to change shape and open its ion channel. There are several kinds, all part of the same family.

26.

The primary purpose of the passage is most likely to

propose a new theory about
Out of Scope: new theory
We're presenting new insights into the working of the brain, but there isn't a new theory. The beginning of the second paragraph is saying that "the theory has gradually won acceptance, but for a long time was known about the mechanism of how the theory worked". This passage is presenting new findings about that mechanism, not presenting a new theory.
10% picked this
introduce evidence that challenges a
Opposite
This passage introduces research insights into a puzzling aspect of a widely accepted theory about the working of the brain. The fact that the evidence the passage introduces is able to explain the mechanism of how chemical neurotransmitters could impact electrical transmission actually strengthens this theory.
12% picked this
describe the approach scientists use
Out of Scope: approach
The bulk of the passage isn't explaining any sort of scientific approach. The main thrust of the passage begins with two of the three classic Main Point pivot words "Recently, however" at the end of the 2nd paragraph. The 3rd paragraph begins "the new evidence shows ..." The 4th paragraph begins "it has also been discovered ..." The passage is mainly about research discoveries, not about a scientific approach.
1% picked this
Correct
discuss new support for a
Why this is right
The beginning of the 2nd paragraph tells us that this theory about the brain (neurons secrete chemicals which enable electrical transmission to take place) took a while, but was eventually accepted by the scientific community (i.e. widely accepted theory). The 2nd paragraph goes on to say "for a long time, little was known about the mechanism", and "in fact, some scientists remained skeptical because they couldn't imagine how it worked". Since this recent research "has gathered enough evidence for a convincing explanation", this is new support for that widely accepted theory.
Skill tested: Primary Purpose · how this choice captures the passage's function is the move to repeat next time.
69% picked this
illustrate the practical utility of
Too Narrow
Too Narrow: practical utility Too Broad: the working of the brain The author does end the passage (as most Old / New passages end), by discussing potential implications of the new research. The last paragraph says, "This discovery is medically significant" because we could get practical benefits such as highly selective brain drugs. But, the practical utility was just one quick bonus observation, not the main story. The way this answer choice is phrased, you would expect to read a passage that was broadly about how researching how the brain works leads to practical applications. You'd be surprised if the first 85% of the passage was specifically about a mystery in the field of brain science about how one neuron transmitted its electrical signal to another neuron.
8% picked this

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