Neural communication depends on chemical signals that shape thought, emotion, movement, and memory. Understanding neurotransmission helps explain how biology influences behavior in mental health, stress responses, and social interaction.

How neurons communicate

When one neuron communicates with another, it does so through neurotransmission.

This process begins when an electrical impulse travels down the neuron to the axon terminal. At the terminal, the neuron releases neurotransmitters into the synapse.

Diagram of a chemical synapse showing how neurotransmitters are released from synaptic vesicles in the presynaptic terminal, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic membrane. This provides a concrete visual map for the sequence of events described in synaptic transmission, including where reuptake and receptor binding occur. Source

Neurotransmission usually follows a sequence:

• an action potential reaches the axon terminal

• vesicles release neurotransmitters into the synaptic cleft

• neurotransmitters bind to specific receptors on the postsynaptic cell

• the receiving neuron becomes more or less likely to fire

• the signal ends through reuptake, enzymatic breakdown, or diffusion

The effect of a neurotransmitter depends on the receptor it binds to. Some signals are excitatory, meaning they increase the chance that the next neuron will fire. Others are inhibitory, meaning they reduce that chance.

Graph of an excitatory postsynaptic potential (EPSP), an inhibitory postsynaptic potential (IPSP), and their summation over time. It illustrates how excitation depolarizes the membrane toward threshold while inhibition hyperpolarizes it away from threshold, and how combined inputs integrate to determine whether an action potential is triggered. Source

Human behavior is influenced by the balance of excitation and inhibition across large neural networks, not by a single chemical acting alone.

Disruptions to neurotransmission can affect mood, attention, memory, movement, and decision-making. For this reason, psychologists and neuroscientists often study neurotransmitters when explaining behavior in clinical, cognitive, and health-related contexts.

Chemical messengers beyond the synapse

Not all chemical communication happens directly between neurons. Some chemical messengers are hormones, which are produced by endocrine glands and carried in the bloodstream.

Compared with neurotransmitters, hormones usually act more slowly but can have longer-lasting effects. Neurotransmitters are often linked to rapid communication in the nervous system, while hormones help regulate broader bodily states such as stress, energy use, and reproduction. Both types of chemical messenger influence behavior, so IB Psychology expects students to apply them in real contexts rather than treat them as isolated facts.

Key neurotransmitters in human behavior

Serotonin

Serotonin is commonly associated with mood, but it also affects sleep, appetite, and some aspects of cognition. Low or dysregulated serotonin activity has been linked to depression and anxiety-related symptoms. However, IB students should avoid overly simple claims such as “low serotonin causes depression.” Human behavior is complex, and serotonin interacts with other neurotransmitters, life experiences, and situational stressors.

Many antidepressant drugs aim to increase the availability of serotonin in the synapse. This shows how knowledge of neurotransmission can be applied in a health context.

Dopamine

Dopamine is involved in reward, motivation, attention, and movement. It is often discussed in relation to pleasure, but its role is broader: dopamine helps the brain identify what is important and worth pursuing. Dysregulated dopamine activity has been linked to addiction, schizophrenia, and movement disorders.

In behavioral contexts, dopamine helps explain why rewarding experiences can strengthen repeated actions. This makes it relevant to habits, substance use, and reinforcement.

Acetylcholine, GABA, and glutamate

Acetylcholine is important for learning, memory, and muscle activation. Reduced acetylcholine functioning has been linked to memory impairment, especially in disorders such as Alzheimer’s disease.

GABA is the brain’s main inhibitory neurotransmitter. It helps calm neural activity and is important in anxiety regulation. If inhibitory control is reduced, a person may become more vulnerable to overarousal.

Glutamate is the brain’s main excitatory neurotransmitter. It is involved in learning and memory, but too much excitation can be harmful. These examples show that healthy behavior depends on balance rather than simply having “more” or “less” of a neurotransmitter.

Applying chemical messengers within contexts

Mental health and treatment

Chemical messengers are especially important in clinical psychology. For example:

• serotonin is often discussed in depression

• dopamine is often discussed in addiction and psychotic symptoms

• GABA is often discussed in anxiety

• acetylcholine is often discussed in memory disorders

Drugs can change neurotransmission by increasing or decreasing a chemical signal. Some act as agonists, increasing the effect of a neurotransmitter, while others act as antagonists, reducing its effect. This helps explain why medication can alter behavior, emotion, and cognition.

Stress and social behavior

Hormones are highly relevant in the context of stress. Adrenaline prepares the body for immediate action by increasing heart rate and alertness. Cortisol supports longer-term stress responses by mobilizing energy.

Labeled schematic of the hypothalamic–pituitary–adrenal (HPA) axis, showing CRH release from the hypothalamus, ACTH release from the anterior pituitary, and cortisol release from the adrenal cortex. The negative feedback arrows help explain why cortisol is both a stress hormone and a regulator of its own production over time. Source

In the short term, these responses can be adaptive. If cortisol remains elevated for long periods, however, attention, sleep, and memory may be negatively affected.

Chemical messengers also influence social behavior. For example, oxytocin has been linked to bonding, trust, and attachment. Still, its effects depend on context. Oxytocin does not simply “cause trust” in every situation; social setting, relationship history, and interpretation of cues all matter.

Why context matters

A strong IB answer should show that neurotransmission does not work in a simple one-cause-one-effect way. The influence of chemical messengers depends on:

• receptor type and receptor location

• interaction with other neurotransmitters or hormones

• dose and duration of the signal

• individual differences

• the social or environmental context in which behavior occurs

This is why psychologists apply neurotransmission within specific contexts such as mental health, stress, learning, or social relationships, rather than making broad claims that one chemical fully explains behavior.