2.1.4—Chemical messengers
- Syllabus
- First assessment 2027
- Objective
- 2.1.4
- Level
- SL
Chemical messengers are signals, not single-cause explanations
Neurotransmitters carry signals across synapses, while hormones travel through the bloodstream; both can influence behaviour by changing how neural systems respond.
A chemical explanation asks how release, receptor binding, reuptake or degradation changes a circuit. The same messenger can have different effects in different pathways, and measured levels may not equal activity at a specific synapse.
A drug that blocks reuptake may increase a messenger's availability, but symptom change depends on receptor adaptation, network effects and the person's context—not only the concentration in blood.
One neurotransmitter is not a single “happiness” or “aggression” chemical. Keep mechanism, measurement and behavioural claim separate.