So what happens in your brain when you eat chocolate, take a pill to alleviate pain, ingest a party drug or go on an ayahuasca journey? Much happens, and there, in our most complicated organ, neurotransmitters are hard at work. Put simply neurotransmitters are chemicals that move from one nerve cell to another – they are the chemical messengers in the brain. The brain is extraordinarily complex with billions of individual, and thousands of different kinds of nerve cells called neurons, with each neuron being made up of branching axons at one end, a trunk and branching dendrites at the other end. Each dendrite connects to a neighbouring neurons axon, which in turn connects a neighbouring dendrite. The whole brain is connected in this way – an intricate mesh of connecting cells.
Signals are conducted along individual neurons as electrical current, but communication between the neurons themselves is mediated by the chemical messengers: the neurotransmitters. More than 50 different kinds have been discovered, most of them in the brain. Some neurons will produce only one kind of neurotransmitter, while others produce two or more. An example of a neurotransmitter is serotonin – an important mood stabiliser, contributing to feelings of wellbeing. Axons of serotonin neurons project all through the brain affecting overall communication. Another neurotransmitter is dopamine which has a whole host of functions including motivation, reward and pleasure.
Here’s how it works. In the nervous system information is transferred when the neurons fire – when the chemical neurotransmitter moves across from one neuron to another, from axon to dendrite, across a tiny gap known as the synapse. Here, at the synapse, receptors in the ends of neurons are specified to accept or reject particular neurotransmitters. A neurotransmitter can be thought of as a key, and a receptor as a lock. If the key – the chemical neurotransmitter, fits the lock – the receptor, then the neuron will fire.
Each neurotransmitter has its own specific family of receptors. Neurotransmitters are released at different rates to ensure the correct amount of message is being sent. As well as stimulating the firing of networks of neurons, importantly neurotransmitters may inhibit the firing of these networks – a sort of breaking mechanism for the brain. This helps keep the old grey matter all nicely balanced. Apparently in people who have schizophrenia, the serotonin breaking system is not functioning properly.
Finally, once the firing has completed, the neurotransmitters are moved out of the receptor back into the synapse and then cleared out of the way – they are re-absorbed back into the original neuron. This is called re-uptake, so that the synapse can be ready to function again.
So the activity of the brain is the firing of millions of neurons causing electrical waves to move across the brain from one region to another. It’s all a quite complicated process and it is this complexity that allows our nerve cells to store and transmit the vast amounts of information needed for us to carouse about in our lives.
Now drugs can enhance or inhibit nerve cell function, or may have no effect at all. Drugs do this by providing neurotransmitters to the nerve cells for use in the synapse. Drugs can also mimic the chemical neurotransmitters in the synapse. So a drug may be similar enough chemically to work in the same way – to fit into the receptor. Also drugs may block the action of neurotransmitters by fitting into a receptor and sort of closing it down. All this activity causes changes in the sensations and emotions that we experience and these experiences vary greatly from one person to another, even with the same drug or chemical.
For an example of how this works let’s look at chocolate. There are over 300 chemicals in chocolate that have varied effects on our nervous system, albeit some very small. So when you eat a piece of chocolate you ingest one of these chemicals – tryptophan – an amino acid. The gut absorbs the amino acid and it enters your bloodstream. Some of this amino acid will find its way to your brain. In your brain the raphe nucleus breaks down the tryptophan into the neurotransmitter serotonin. From here it makes its way through blood vessels to various serotonin neuron sites and the serotonin is deposited at the synapse. So one could say that there is more serotonin swimming around at the synapse and this helps the cell to fire more readily giving you a little lift in mood. This is simplified but it gives one a glimpse of the workings.