Self-study
P1
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). ███
Neurobiologists' traditional hypothesis ·
Brain works exclusively by electric signals
Brain cells communicate because electrical impulses jump gaps between neurons.
Alternative hypothesis ·
Electrical impulses are transmitted chemically between neurons
Neurons secrete a chemical neurotransmitter that binds with a receptor molecule in another neuron. This makes the receptor neuron permeable to ions, and movement of ions creates an electrical impulse. (No need to try to remember the details of this causal mechanism.)
P2
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Unknown causal mechanism ·
Alternative theory is accepted, but took long time to discover how neurotransmitters work
Hypothesis for causal mechanism ·
Structure of receptors help convert chemical signals to electrical impulse
P3
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Neurotransmitter-gated ion channels ·
Neurotransmitters have a binding site and a channel for ions
(Going to come back for the details here. Just need to understand there's a combo of a binding site and channel for ions to pass through.)
P4
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Variety in neurotransmitters ·
Receptors in one part of brain are different from receptors in other parts
Implication of variety ·
Ability to make drugs targeted to specific receptors
This could help alleviate many different brain disorders.
Passage Style
Phenomenon-hypothesis (RC)
Single position
24.
The author most likely uses ███ ██████ █
a
possess channels for ████
“Defined categories of neurons” doesn’t make sense as a reference to neurons that have ion channels, because the drugs are supposed to work by affecting ion channels — this presumes that all the relevant neurons have ion channels. So the possession of ion channels wouldn’t be a way to define different categories of neurons.
b
respond to drug █████████
“Defined categories of neurons” doesn’t make sense as a reference to neurons that respond to drug treatment, because this reference doesn’t offer a way to distinguish different categories of neurons. The drugs are supposed to work by affecting neurons — so all of the neurons that are relevant to how these drugs work would respond to the drugs. We want to know why certain categories of neurons relate to selectively treating different disorders.
c
contain receptor molecules
“Defined categories of neurons” doesn’t make sense as a reference to neurons that contain receptor molecules, because all the relevant neurons have receptor molecules. So the possession of receptor molecules wouldn’t be a way to define different categories of neurons.
d
influence particular brain █████████
This best captures the meaning. Drugs might target receptors on “defined categories of neurons” so that the drugs can treat certain brain disorders. How would these drugs work? By targeting neurons associated with particular brain functions. Some neurons, for example, might be associated with mood disorders, others with stroke, others with Alzheimer’s. By targeting the neurons associated with a specific kind of disorder — in other words, a defined category of neuron — the drug might help ameliorate the effects of the disorder.
e
react to binding ██ █████████████████
“Defined categories of neurons” doesn’t make sense as a reference to neurons that react to binding by neurotransmitters, because all the relevant neurons react to neurotransmitters. So the quality of reacting to binding by neurotransmitters wouldn’t be a way to define different categories of neurons.