Neurotransmitters are the key to how our brain thinks, feels and acts. Zoomed in, they act as a kind of variable switch between two neurons, allowing a signal to pass through or not. The biological chemicals that we as neurotransmitters use are repurposed hormones. A deficit in availability, or oversupply of any one of these neurotransmitters is the root cause of the majority of mental ill health and can be a cause of many other conditions not considered to be Mental Health.

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Understanding Neurotransmitters

Neurotransmitters are biological chemicals, generally hormones, that also serve the purpose of temporarily connecting one neuron to another to send a signal. This connection is very fast and last only a brief amount of time, triggering up to hundreds of times a second. The Neurotransmitter is effectively a kind of switch that either by its presence allows the signal through, or by its absence, doesn’t.

Of course, it is far more complicated than that. What follows explains, still fairly simplistically, how that works.

A neuron is a cell in your brain that makes decisions. It receives signals from up to 20 thousand other neurons, then it makes a decision. That decision may be to do nothing, or send a signal to tens or thousands of other neurons.

In a similar way to modern electronics, each neuron has a particular set of calculations it can do, and in combination, that can do lots of interesting things. In modern electronics, we have certain kinds of logic circuits called “Logic Gates”, where two signals result in a single output. For example, a logic gate might be an AND gate, where both input wires need to have some electrical charge for the output to be charged. An OR gate, on the other hand, is where one wire or the other needs to be charged, but not both, to give a charged output.

Our neurons are incredibly complicated logic gates. Unlike our electrical analogues, each neuron can perform lots of different gate functions, depending on which signals it receives. Each different triggered function from the input will create a range of different outputs. This is why our brains are so much more powerful and flexible than a computer circuit.

Picture of parts of a neuron and how the axon reaches out to touch another neuron. Drawing by BruceBlaus, commons from wikimedia.
By BruceBlaus – Own work, CC BY 3.0,

Let us now look at how a signal travels from one neuron to another. From the central neuron mass, a projection called an Axon Hillock extends a long tendril called the Axon. It is much like a tree trunk, which branches out to one or more other neurons. The Axon makes it almost all the way to a neuron, almost touching a spike called a Dendrite. The gap between the Axon and the Dendrite is called the Synaptic Gap, and often just referred to as a Synapse.

By ScientificAnimations dot Com/, CC BY-SA 4.0,

Human brain signals are electrical in nature, much like our electronics. Rather than electrons flowing through metal, biology uses ionic flow. Ionic flow is where charged particles move through a fluid to carry the signal. Charged particle signals are much slower than electronic signals.

The Synaptic Gap is filled with a mostly inert fluid. That is, the fluid itself won’t pass a signal from the Axon to the Dendrite. This is basically the “off” state. The source Neuron receives various signals from other Neurons which results in a calculation in the central Neuron mass. In this example, the result of the calculation charges the Axon Hillock, which triggers an ionic signal to cascade down the dendrite. A way to think about this is somewhat similar to dominos falling and knocking the next domino over, each domino passes on a signal, a change in ion charge. Imagine that the bottom of the domino is on a flexible stand that after being stressed by the tipped domino, stiffens up, straightening the domino ready to receive a new signal.

The elements that make this signal are made of calcium and sodium, and they go back and forth along a membrane through holes called gates, that travels the length of the axon. Calcium Channel Blockers and Sodium Channel Blockers making it harder for this signal to go down the axon in different ways, slowing the signal speed. This is thought to help some kinds of disorder such as epilepsy, some heart conditions and some kinds of anxiety.

When the signal gets to the end of the axon, the end at the synapse becomes charged with electrical potential. When the charge gets high enough it triggers the release of neurotransmitters stored in the axon end in little chambers called vesicles or reservoirs. The neurotransmitter is excreted into the gap, which now passes the charge that has built up at the end to reach the other side, the receptor of that neurotransmitter.

This is effectively the “on” state.

After the Axon end has lost sufficient charge, the fluid in the gap is swept clear, some neurotransmitter is recycled, most is flushed, all reset to pass a signal again. Meanwhile the dendrite is passing the received signal to the Neuron it is part of in a similar way to how the Axon passed its signal.

{Further Reading : Synaptic Transmission [Link]}

Synapse Neurotransmitter Simulator

An experiment to simulate this is to connect one end of a battery to a suitable light globe. Connect the other end of the battery to a wire that goes into a cup. The wire end in the cup should be stripped of insulation. Another wire in the cup, not touching the first wire, goes from the cup to be connected to the other end of the light globe. If it is an LED you are using, check that you have the LED connected in the right direction. Much like an LED, the Axon, Synapses and Dendrite have only 1 direction that they work in. Poor into the cup some distilled water. The LED should be unlit – this is the “off” state.

The cup is the Synaptic Gap with inert fluid in it.

Now add a teaspoon of common table salt to the cup and gently stir it. If the LED has not started to glow, add another teaspoon. Keep adding salt until the LED lights up. You have now added enough of the Neurotransmitter analogue to the Synaptic Gap to pass the signal on. Once you see the light, tip the water in the cup out and put some new distilled water in it to reset the switch.


There are many neurotransmitters used by different types of neurons to send signals across the synaptic gap. We will examine a few of the most important neurotransmitters in mental health.


  • Dopamine
  • Noradrenaline (Norepinephrine)
  • Adrenaline (Epineprhine)
  • Serotonin
  • Melatonin
  • Histamine


  • Oxytocin
  • Endorphins

Amino Acids

  • Glutamate
  • GABA (Gamma-Amnibutryric Acid)

Dopaminergic Neurons / System

  • Protein (eaten in food)
  • Tyrosine is made from protein via digestion, which is then converted to L-Dopa (Levodopa)
  • L-Dopa passes the Blood Brain Barrier (the Dopamine made in your adrenal gland can’t, which is why you don’t treat ADHD by ingesting or injecting Dopamine)
  • Dopamine is made by recombining L-Dopa from your blood in the brain (first link in Dopaminergic chain)
    • Empower the Executive Function
      • Concentration
      • Holds short term ideas / data (like mental math rather than writing it down)
      • Problem solving, creative solutions, finding more complex viable answers than the Emergency Centre
      • Big picture task prioritisation
      • Comprehension and connecting ideas, integral to learning concepts
    • Being alert, present and higher levels of thinking
    • Manages Muscle Movement
    • Reinforces activities that improve ancient human survival, aka The Reward System
      • Enjoying food
      • Aquiring goods (browsing shops and or buying goods)
      • Learning
      • Positive Social
      • Creating

There are five types of dopamine receptors, which include D1, D2, D3, D4, and D5. Each receptor has a different function and is found in different locations.

The function of each dopamine receptor[4]:

  • D1: memory, attention, impulse control, regulation of renal function, locomotion
  • D2: locomotion, attention, sleep, memory, learning
  • D3: cognition, impulse control, attention, sleep
  • D4: cognition, memory, fear, impulse control, attention, sleep
  • D5: decision making, cognition, attention, renin secretion

The five different dopamine receptors can subdivide into two categories. D1 and D5 receptors group together (Dop Alpha for here), and D2, D3, and D4 are together in a separate subgrouping (Dop Beta). 

{D1 to D5 receptors, source: Biochemistry, Dopamine Receptors [Link]}

  • Norepinephrine is made from unused Norepinephrine
    • Situational Assessment via Sensory interpretation and Focus
      • Hyperfocus vs distractability vs impulsiveness
    • Feelings / Mood / Emotions
      • Freeze / Flight / Fight / Fawn reflex when an emergency is detected
    • Connects “want” and “plans” to “physical actions”
    • Manage pain perception, ties in with Endorphins (we think)
  • Epinephrine (aka Adrenaline) is made from unused Norepinephrine
    • At high levels, disengages the higher thinking centre and engages primal survival actions, supresses pain perception
    • At moderate levels, appears to be connected to long term memory storage

  • Serotonin is made from the amino acid component of protein called tryptophan
    • Powers the neurotransmitter homeostatic system (prompting direct creation/deletion of neurotransmitters to get to he Goldilocks Zone where able) – this is currently conjecture and we need more studies to confirm this
    • First link to decrease alertness/agitation (soporiphic/sleep, parasympathetic trigger)
  • Melatonin is made from unused Serotonin, and also from your bodies adrenal gland as this last link in the Dopaminergic chain can pass through the Blood Brain Barrier
    • High levels, prompts the brain to consider sleeping now if the adrenal level is low
      • Being in darkness / dim light prompts the body to produce Melatonin
    • Low levels, prompts the brain to be awake
      • Bright light / daylight (especially sky blue) prompts the body to delete Melatonin

{Biochemistry, Seotonin [Link]}

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