5.8 Neurotransmitters

What neurotransmitters do

Neurotransmitters are chemical messengers released from a neuron's axon terminal into the synapse, binding to receptors on the next neuron. This can either excite (increase likelihood of firing) or inhibit (decrease likelihood of firing) the receiving neuron. Imbalances in neurotransmitter levels are linked to various psychological disorders and behaviors.

Key neurotransmitters & functions

Acetylcholine (ACh): muscle movement, learning, memory (low levels linked to Alzheimer's). Dopamine: reward, movement, motivation (linked to Parkinson's [too little] and schizophrenia [too much]). Serotonin: mood, sleep, appetite (linked to depression). Norepinephrine: alertness, arousal, fight-or-flight (linked to depression). GABA: main inhibitory neurotransmitter, reduces anxiety. Glutamate: main excitatory neurotransmitter, involved in learning/memory.

Drugs and neurotransmitters

Agonists are drugs that increase a neurotransmitter's action by mimicking it or increasing its release. Antagonists block or reduce a neurotransmitter's action by blocking receptors. Reuptake inhibitors (e.g., SSRIs) block the reabsorption of a neurotransmitter, prolonging its effects in the synapse — commonly used to treat depression by boosting serotonin availability.

Key terms

Acetylcholine (ACh)

Involved in muscle movement, learning, and memory; low levels linked to Alzheimer's disease.

Dopamine

Involved in reward, movement, and motivation; too little linked to Parkinson's, too much linked to schizophrenia.

Serotonin

Regulates mood, sleep, and appetite; low levels linked to depression.

Agonist vs. Antagonist

Agonist: mimics/increases neurotransmitter effect. Antagonist: blocks/reduces neurotransmitter effect.

GABA

The brain's main inhibitory neurotransmitter; reduces neural activity and anxiety.

Try an AP-style question

Which neurotransmitter is likely low?

1. Serotonin
2. GABA
3. Dopamine
4. Acetylcholine