Influences on Behaviour

Agonist = increases signaling along a pathway (activates/mimics); antagonist = blocks the receptor, decreases signaling.
Catecholamines (all synthesized from tyrosine): epinephrine (fight-or-flight), norepinephrine (alertness/attention/arousal), dopamine (motivation/reinforcement + movement).
Serotonin: mood, sleep, appetite, digestion — linked to depression/anxiety; many antidepressants boost serotonin signaling.
GABA = primary inhibitory neurotransmitter (calms, anti-seizure); glutamate = primary excitatory neurotransmitter (drives synaptic plasticity/learning) — opposite jobs, similar-sounding names.
Acetylcholine: neuromuscular junction (muscle contraction) + attention/learning/memory in brain — its loss is linked to Alzheimer's disease (nucleus basalis of Meynert).
Adrenal medulla → epinephrine/norepinephrine (fast fight-or-flight); adrenal cortex → cortisol (long-term stress/metabolism) + aldosterone (BP/fluid balance).
Family, twin, and adoption studies each control for a different confound when separating genetic vs. environmental contributions to behavior.

Agonist: Increases signaling along a pathway by activating a receptor or mimicking its neurotransmitter.
Antagonist: Blocks a receptor, preventing the neurotransmitter's usual effect and reducing signaling.
Endorphins: Endogenous opioid-like molecules; reduce pain perception, improve mood; released during intense exercise.
Concordance rate: The probability that both twins in a pair show the same trait or disorder.
Monozygotic twins: Identical twins from one fertilized egg that splits — share nearly all genetic material.
Dizygotic twins: Fraternal twins from two separate fertilized eggs — share ~50% of genes, like ordinary siblings.

GABA	Glutamate
Primary inhibitory neurotransmitter in the CNS	Primary excitatory neurotransmitter in the CNS
Makes neurons less likely to fire; calming	Makes neurons more likely to fire
Too little → seizures	Drives synaptic plasticity (learning/memory); too much → excitotoxicity
Anti-anxiety meds/sedatives enhance it	—

Adrenal Medulla	Adrenal Cortex
Releases epinephrine/norepinephrine	Releases cortisol and aldosterone
Immediate fight-or-flight response	Longer-term stress response, metabolism, fluid/BP regulation

Study Type	What It Controls For / Shows
Family study	Trait runs in biological relatives more than general population — but can't separate shared genes from shared environment
Twin study	Higher concordance in monozygotic vs. dizygotic twins → evidence for genetic contribution (not a fixed %)
Adoption study	Compares adopted individuals to biological vs. adoptive relatives — separates genetics from environment more cleanly

GABA and glutamate sound similar but have opposite jobs — GABA inhibits, glutamate excites.
Dopamine is more than "the pleasure neurotransmitter" — it's about motivation, reinforcement, and assigning significance to experiences, plus a major role in movement.
Concordance rate ≠ heritability — a higher rate in monozygotic vs. dizygotic twins is evidence genetics contributes, not a precise measurement of how much.
Endorphins reduce pain, but they don't cross the blood-brain barrier easily — the endocannabinoid system is a leading candidate for "runner's high" euphoria, not endorphins alone.

What amino acid are epinephrine, norepinephrine, and dopamine synthesized from?

Which neurotransmitter is the primary inhibitory transmitter in the CNS?

Loss of which neurotransmitter-producing neurons is linked to Alzheimer's disease?