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passage 4
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
Single position
23.
Each of the following statements ██ ████████ ██ ███ ███████ ███████
a
The secretion of ███████ █████████ █████ █ ████ ██ ██████ ██████████████
b
The flow of ████ ███████ ███████ █████ █ ████ ██ ██████ ██████████████
c
The binding of █████████████████ ██ █████████ █████ █ ████ ██ ██████ ██████████████
d
The structure of █████████ ██ ██████ ████████ █████ █ ████ ██ ██████ ██████████████
e
The size of ████████████████ ███████ █████ ██ █████████ █████ █ ████ ██ ██████ ██████████████