Study topic · about 3 minutes

Neurotransmitters

Neurotransmitters are chemical messengers that carry signals across the tiny gap between neurons, the synapse. Some, like glutamate, excite the next cell; others, like GABA, calm it down. A few, like dopamine and serotonin, come from small groups of neurons deep in the brain and tune whole networks for reward, mood and sleep.

Key points

Excitatory neurotransmitters make the next neuron more likely to fire; inhibitory ones make it less likely.
Glutamate is the brain's main excitatory messenger, and GABA is its main inhibitory one.
Dopamine comes from the substantia nigra and the ventral tegmental area, serotonin from the raphe nuclei, and norepinephrine from the locus coeruleus.
Many drugs copy a neurotransmitter (agonists), block it (antagonists) or keep it in the synapse longer (reuptake inhibitors).

How do neurotransmitters work?

When an action potential reaches the end of an axon, tiny bubbles called vesicles release neurotransmitter into the synapse. The molecules drift across and fit into receptors on the next cell, like keys in locks. Then the signal is switched off: the neurotransmitter is broken down, or pumped back into the neuron that released it, which is called reuptake.

The main neurotransmitters and what they do

Neurotransmitter	Main jobs	Linked to
Glutamate	The main "go" signal: excites neurons, and is key to learning and memory.	In excess it can kill neurons, for example after a stroke.
GABA	The main "stop" signal: calms neurons down.	Anti-anxiety medicines and alcohol boost its effect.
Dopamine	Reward, motivation and movement.	Parkinson's disease (too little in movement circuits), addiction, schizophrenia.
Serotonin	Mood, sleep, appetite and calm.	Depression; many antidepressants raise it.
Norepinephrine	Alertness, attention and the stress response.	Some treatments for depression and ADHD.
Acetylcholine	Moves muscles, and helps attention and memory in the brain.	Alzheimer's disease (it declines), myasthenia gravis.
Endorphins	Natural painkillers, released during pain and stress.	Opioid drugs act on the same receptors.
Substance P	Carries pain signals.	Pain; endorphins can block its release.

Where are they made?

Glutamate and GABA are used by neurons all over the brain. Several others come from small clusters of cells whose axons spread far and wide:

Dopamine: the substantia nigra, for movement through the basal ganglia, and the ventral tegmental area, for reward through the nucleus accumbens and prefrontal cortex.
Serotonin: the raphe nuclei, along the middle of the brainstem.
Norepinephrine: the locus coeruleus, in the pons.
Acetylcholine: motor neurons, for muscles, and groups of cells at the base of the forebrain, for attention and memory.
Endorphins: the pituitary gland and the hypothalamus, among others.

Watch a dopamine synapse fire in 3D

How drugs change neurotransmitters

Agonists copy a neurotransmitter or boost its effect. Opioids like morphine act on endorphin receptors.
Antagonists block receptors. Some antipsychotic medicines block dopamine receptors.
Reuptake inhibitors stop a neurotransmitter from being pumped back, so it stays in the synapse longer. SSRI antidepressants do this for serotonin; cocaine does it for dopamine.

Over time the brain adjusts to a drug, so more is needed for the same effect (tolerance), and stopping causes withdrawal. Nearly all addictive drugs raise dopamine in the nucleus accumbens, the center of the brain's reward circuit.

Neurotransmitters and hormones

Hormones are chemical messengers too, but they travel in the blood and act more slowly and widely. Some chemicals do both jobs: norepinephrine is a neurotransmitter in the brain, and its close relative adrenaline (epinephrine) is a hormone from the adrenal glands. Other hormones that shape behavior include melatonin, for sleep, from the pineal gland; oxytocin, for bonding, released by the pituitary gland; and leptin and ghrelin, which signal fullness and hunger.

Quick quiz

6 questions. Your answers are saved and come back in your daily review.

Which neurotransmitter is the brain's main "stop" (inhibitory) signal?
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GABA. GABA makes neurons less likely to fire; glutamate is the main "go" signal.
Parkinson's disease comes from losing dopamine neurons in which structure?
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Substantia nigra. The dopamine cells of the substantia nigra drive the basal ganglia; losing them makes movement slow and stiff.
Most of the serotonin in the brain comes from which cell groups?
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Raphe nuclei. The raphe nuclei run along the middle of the brainstem.
SSRIs, a common kind of antidepressant, work by...
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Blocking the reuptake of serotonin. Selective serotonin reuptake inhibitors keep serotonin in the synapse longer.
Which neurotransmitter do motor neurons release to move your muscles?
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Acetylcholine. Acetylcholine crosses from motor neurons to muscle fibers.
The center of the reward circuit, where nearly all addictive drugs raise dopamine, is the...
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Nucleus accumbens. The nucleus accumbens receives dopamine from the ventral tegmental area.

In these study guides

MCATNeurons, the nervous system and hormones
AP Psychology1.3 The neuron and neural firing
Intro psychologyNeurons and the nervous system (sections 3.2 and 3.3)
Anatomy and physiologyNervous tissue (chapter 12)
NursingNeuro basics
A-level PsychologyNeurons and synaptic transmission

Take it further in 3D

Emotion and rewardFear, drive and the value of things. A short guided lesson in the 3D app.
The basal gangliaChoosing which movement goes. A short guided lesson in the 3D app.

Sources

What are neurotransmitters?, Queensland Brain Institute, University of Queensland
Anatomy and Physiology 2e, 12.5 Communication Between Neurons, OpenStax

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