The nervous system is controlled by electrical and chemical signals between nerve cells called neurons. These neurons (shown below) communicate with each other through chemicals called neurotransmitters. When a neuron receives an electrical impulse of a certain magnitude, it travels from the dendrites to the axon and down to the axon terminals. This is called an action potential. The neurotransmitters are stored in the axon terminals, and are released into the synapse, which is the space between two neurons. These neurotransmitters fit into the dendrites of the receiving neuron like a lock and key and set off an action potential in that neuron, creating a chain reaction.
(from https://medicalxpress.com/news/2018-07-neuron-axons-spindly-theyre-optimizing.html)
Different neurotransmitters produce different psychological and physiological responses. For example, serotonin affects mood, hunger, sleep, and arousal. Low levels of serotonin lead to adverse effects. Chronically low levels of serotonin lead to clinical depression. Agonist drugs can mimic the effects of certain neurotransmitters, which is why Prozac has proven to be effective in treating depression by imitating serotonin in the body.
Even people who do not have a clinical mental illness are affected by different levels of neurotransmitters on a daily basis, and there are different ways that we can naturally increase serotonin levels. My favorite way to improve my mood by increasing neurotransmitter levels is exercise. Most runners describe a “runner’s high” after intense physical activity. Of course, this is different from getting high from drug use, but some components are similar. Like Prozac, many recreational drugs are agnostic drugs that mimic the effects of serotonin and other mood-enhancing neurotransmitters. Exercise causes the body to naturally produce more serotonin and endorphins, which improves the mood.
A little bit of exercise can make a big difference. Sometimes I jog for ten minutes if I don’t have time for a full workout, and even that is enough to improve my mood for the rest of the day. Understanding the biology of why we feel the way we do can help us to make choices that improve our overall mental health.