What structure is like a locked door that only certain neurotransmitter keys can unlock?
a. synapse
b. receptor site
c. neutral chiasm
d. response terminal
e. synaptic vesicle

The answer to this question would be: B. Receptor site 

The receptor site of a neurotransmitter often only receives a specific kind of transmitter. That was because the receptor has a unique 3D structure, so different transmitter wouldn't fit into the receptor. That was similar to lock and key principles.

It settles nerves, reduces the tension.

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