Clear Science!

There are other neurotransmitters besides serotonin in the brain that contribute to the feeling of being in love. Dopamine is a neurotransmitter that is essential to voluntary motion and cognition. (Insufficient dopamine results in Parkinson’s Disease, as seen in the movie Awakenings.) Dopamine also regulates motivation and the reward system, related to love through desire.

Norepinephrine is similar to adrenaline, resulting in an increased heart rate and preparing the body for stress. Oxytocin causes sexual arousal and increases trust, bonding, and maternal behavior.

Many neurotransmitters, such as these, also act as hormones. Hormones are molecules that accomplish signaling using the bloodstream, rather than across a synapse. Because of the blood-brain barrier, these actions are different, and these molecules also cause reactions in other parts of the body besides the brain.

Your brain and nervous system are networks of neurons signaling to each other. We talked about how neurons signal to each other across a synapse. Neurotransmitters are simple chemicals that cross a synapse to accomplish this signaling. They are released from one neuron’s axon, cross the synapse, and bind to receptors on the other neuron. Abundance or scarcity of certain neurotransmitters correlate to “feelings” you experience.

Serotonin is a neurotransmitter associated with feelings of calm and well-being. It is sometimes called 5-HT, which is a short form of its chemical name, and it is derived from the amino acid tryptophan. (This is the basis of the urban legend that turkey makes you happy via chemistry.)

Low levels of serotonin are thought to be associated with obsessive-compulsive disorder and depression. But what about the original question about love? Some studies have suggested that serotonin levels are low in people who are newly in love. This makes some sense, as this state is not calming, and does involve some compulsive behavior.

Incidentally, some anti-depressants called SSRIs work by blocking reuptake of serotonin back into the pre-synaptic neuron. This results in more serotonin in the synapse for a longer time, to achieve a calm feeling.

Neurons are the cells that make up your nervous system, including your brain and spinal cord. A schematic is shown above, as well as a photograph of some actual neurons. One of the most important things about neurons is that they form a network, via a large number of connections they make to other neurons.

There are several different kinds of neurons, which all look a bit different, but generally there will be: a cell body (where the nucleus is), dendrites coming off the cell body, and the axon, which is long and branched. Connections between neurons are made when an axon terminal comes close to the dendrites or cell body of another neuron.

A synapse is the small gap made at this connection point. Neurons can signal to each other electrically or chemically. A chemical synapse is 20 to 40 nanometers across. Chemicals called neurotransmitters are passed across the synapse for signalling.