Our brain is one of the most powerful and intricate centers of our body. It, along with the rest of the nervous system, controls everything that we do. One thing that a lot of people often forget about the nervous system is the crucial role neurotransmitters play in the process. Neurotransmitters are like chemical messengers, carrying signals from one neuron to the next. But, before we get into neurotransmitters, let us first understand the function of the neuron.
We have a few key types of neurons. Afferent neurons communicate sensory experiences towards the brain; efferent neurons transfer messages to trigger responses from organs and muscles; and interneurons serve as the “middle man” between afferent and efferent neurons. Neurons have three simple tasks they must fulfill: receive information, carry information down its length, and pass on information. More specifically, though, the dendrites (which are these fine, selectively permeable, branch-like fibers) receive the information from a neuron and pass it onto the cell body, which essentially “filters” through these messages, selecting the appropriate ones to then pass onto the axon. The axon is this long fiber that the information travels down to be delivered to another neuron through the terminal branches (junctions that join cells).
Interestingly enough, our neurons never actually touch each other when transmitting information. Between neurons exists the synapse, a gap that prevents electrical charges from being passed across. This is because, in the terminal buttons, synaptic transmission occurs where the electrical charges are turned into chemical messages. Now, this is where neurotransmitters come in. The terminal buttons carry these small sacs called synaptic vesicles, which contain, you guessed it, neurotransmitters – the vital chemicals needed for neural communication. When the action potential, the electrical charge that travels down the axon, reaches the synaptic vesicles, the sacs burst to release the neurotransmitters. The neurotransmitters then have to try to fit themselves into their respective receptor sites on the receiving neuron. Think of it like a puzzle piece where the neurotransmitters are the pieces trying to find their spot on the puzzle.
Like puzzle pieces, neurotransmitters come in all different shapes and sizes. There are so many types of neurotransmitters and they all have unique purposes. Some of the neurotransmitters that you might have heard of include dopamine and serotonin. Dopamine is generally involved in movement, learning, attention, and emotion. More specifically, it plays a big role in our brain’s “reward system,” which is why people commonly associate dopamine as a “feel-good” hormone. Hence, when we do an activity that gives us pleasure, such as eating a cookie, dopamine is released from our neurons (“Dopamine,” 2022). This dopamine is created in neurons around the base of the brain through two processes: tyrosine, an amino acid, is first turned into L-Dopa (also an amino acid), which is then transformed into dopamine with the help of enzymes (Watson, 2024). When we have the right amount of dopamine, we are able to feel happy, motivated, and focused. However, when we get an excess or undersupply of dopamine, we feel experiences on two ends of the spectrum, from euphoric to unhappy. There are also specific diseases associated with different levels of dopamine, and the same goes for other neurotransmitters. For example, an excess amount of dopamine often correlates to schizophrenia, while an insufficient amount results in Parkinson’s disease. Serotonin, on the other hand, influences mood, hunger, sleep, and arousal. It is like a regulator for our emotions. At normal levels, it keeps us emotionally stable and content. However, when we don’t get enough serotonin, depression usually arises, which is why many depression or anxiety medications aim to increase your serotonin. While dopamine and serotonin are similar in many ways as they are both “feel-good hormones,” serotonin moreso controls the general state of our emotions while dopamine is associated with that rush of happiness from our body’s reward system.
The next neurotransmitter I want to highlight is acetylcholine (ACh). ACh mainly enables our muscle movement, as well as our memory and learning in our brain nerve cells. ACh is created at the end of nerve cells when acetyl and choline groups react from the enzyme choline acetyltransferase. It is particularly important in our autonomic nervous system, which controls all of our involuntary bodily processes involving our internal organs. Alzheimer’s disease is often correlated with a low supply of ACh in the brain, which is why one of Alzheimer’s main characteristics is poor memory and inability to learn (“Acetylcholine,” 2022). Norepinephrine, another type of neurotransmitter, is involved with our “fight or flight” response. It controls our alertness and arousal in stressful situations. Once our brain detects danger, the norepinephrine sends signals to different parts of our body where specific reactions are triggered, such as our eyes dilating or our heart pumping faster.
Gamma-aminobutyric acid (GABA) and glutamate are the other two major neurotransmitters. GABA is a major inhibitory neurotransmitter, while glutamate is an excitatory neurotransmitter. This means that GABA helps prevent things like tremors, seizures, and general excitement and regulates anxiety or fear. It calms our body by blocking the amount of chemical messages or stimulation between nerve cells. This is because when GABA binds to its corresponding receptors – either GABA-A or GABA-B – the responsiveness of the cell is reduced (“Gamma-Aminobutyric,” 2022). Glutamate is the opposite as it stimulates our brain cells, encouraging chemical messages to be transferred. Glutamate is a major and important excitatory neurotransmitter, which is supported by the fact that it is able to bind to four different receptor sites. One of glutamate’s main functions includes learning and memory as its ability to send messages quickly allows our brain to effectively retain information (“Glutamate,” 2022). Overall, it is important we have a balanced and cohesive relationship between GABA and glutamate.
Drugs and medications work with our neurotransmitters in order to function. There are three types of drugs: agonists, antagonists, and reuptake inhibitors. Agonists excite by making neurons fire and amplifying or imitating certain sensations. Remember the puzzle piece reference I made earlier? Agonists replicate the neurotransmitter’s shape close enough to be able to fit in the receptor sites and create the same effect on the receiving neuron. Antagonists, in contrast, stop neural firing by blocking the absorption of neurotransmitters. The shape of the antagonist is similar enough to the neurotransmitter to be able to occupy the receptor site and prevent any action from happening. However, unlike the agonist, it is not alike enough to fully simulate the sensation. Reuptake inhibitors, as the name suggests, block the reuptake of neurotransmitters. This means that the neurotransmitters are forced to stay in the little gap of the synapse, amplifying the effects of the neurotransmitter.
What are some examples of drugs influencing our neurotransmitters? Caffeine is something I’m sure we’ve all tried before. Caffeine wakes us up by increasing the amount of excitatory neurotransmitters released and blocking adenosine, which is an inhibitory neurotransmitter that encourages sleep and decreases alertness. Another example is curare, which is a substance often used to hunt and kill animals by paralyzing them. It does this by blocking the ACh receptors, which usually control our muscle movement.
In conclusion, neurotransmitters are a pillar to not only the nervous system but nearly all processes going on in our body, from our emotions to our movement to our memory. On the surface, we say the brain controls our body, but if we look closer, our neurotransmitters are the secret superheroes that save the day. As scientists and doctors do more research, I look forward to seeing how we can make use of the function of neurons to discover more effective treatments for diseases or conditions linked to neurotransmitters.
Works Cited
*References the Barron’s AP Psychology 2024 textbook
Acetylcholine (ACH). Cleveland Clinic. (2022, December 30). https://my.clevelandclinic.org/health/articles/24568-acetylcholine-ach
Dopamine. Cleveland Clinic. (2022, March 23). https://my.clevelandclinic.org/health/articles/22581-dopamine
Gamma-Aminobutyric Acid (GABA). Cleveland Clinic. (2022, April 25). https://my.clevelandclinic.org/health/articles/22857-gamma-aminobutyric-acid-gaba
Glutamate. Cleveland Clinic. (2022, April 25). https://my.clevelandclinic.org/health/articles/22839-glutamate
Watson, S. (2024, April 18). Dopamine: The pathway to pleasure. Harvard Health Publishing. https://www.health.harvard.edu/mind-and-mood/dopamine-the-pathway-to-pleasure