Wow, thats a great question! It shows that you have an inquiring mind. You want to know HOW we know things instead of just taking things for granted. You are clearly thinking about what we can tell directly and what we cant. As you have noticed, there are lots of things in science that we cant see directly. We have to infer what is going on from what we can observe. An inference is a conclusion we reach after analyzing our observations.
We cant see the neurotransmitter molecules themselves, but we can see more than you might think. Check out the picture at image. There is a photograph from an electron microscope, which can magnify things a lot more than a regular microscope. The little balls labeled presynaptic vesicles are bags of neurotransmitters. When this neuron fires, the neurotransmitters will be released into the synapse. Then they can cross over and fit into receptors on the next neuron. If there are enough of them, the second neuron will fire. Most of what we know about how neurotransmitters work is not from what they look like.
Scientists learn how they work by changing the levels of different chemicals. Researchers can measure what happens when they:
Add more neurotransmitter
Add a chemical that works the same as the neurotransmitter
Add a chemical that blocks the receptors for the neurotransmitter
Add an enzyme to break down neurotransmitters in the synapse
Add a chemical that destroys the enzyme that breaks down neurotransmitters in the synapse
They can use an instrument to measure whether the neuron on the other side of the synapse fires more or less when they do these things. Which of these chemicals will make the second neuron more likely to fire and which will make it less likely to fire? If these kinds of questions interest you, you may want to think about a career as a neurobiologist. Heres a site that will give you more information about doing that: information. Thanks for asking,
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