Past Papers · SAQ
Neurotransmitters: Receptors & Functions
2026A Q05
Exam questionFor each neurotransmitter listed below:
a) acetylcholine (ACh),
b) gamma-aminobutyric acid (GABA),
c) noradrenaline (NorAd),
d) serotonin (5-HT). Outline the following: i) target receptors, including type and location (15% of marks per neurotransmitter), Downstream receptor mechanisms NOT required. ii) functional role(s) (10% of marks per neurotransmitter).
CICMWrecks answer
Master answer
Acetylcholine
| Receptor | Type | Major locations |
|---|---|---|
| Nicotinic NM | Ionotropic ligand-gated cation channel | Skeletal muscle neuromuscular junction |
| Nicotinic NN | Ionotropic ligand-gated cation channel | All autonomic ganglia, adrenal medulla, CNS |
| M1 | Metabotropic | CNS; autonomic ganglia |
| M2 | Metabotropic | Heart, particularly SA and AV nodes; CNS |
| M3 | Metabotropic | Smooth muscle and glands: airways, GIT, bladder, secretory glands; vascular endothelium |
| M4 / M5 | Metabotropic | Predominantly CNS |
Functional roles
- Skeletal muscle contraction at the neuromuscular junction.
- Transmission through all autonomic ganglia.
- Principal postganglionic parasympathetic neurotransmitter.
- Sympathetic cholinergic transmission to sweat glands.
- CNS modulation of arousal, attention, learning and memory.
GABA
| Receptor | Type | Major locations |
|---|---|---|
| GABAA | Ionotropic ligand-gated Cl⁻ channel | Widespread throughout CNS; postsynaptic and extrasynaptic receptors including cortex, limbic system, cerebellum and retina |
| GABAB | Metabotropic GPCR | Widespread CNS and spinal cord; presynaptic and postsynaptic |
Functional roles
- Principal inhibitory neurotransmitter in the CNS.
- Limits neuronal excitability and raises seizure threshold.
- Contributes to sedation, sleep and control of consciousness.
- Modulates motor tone and spinal reflexes.
- Important in anxiety and spasticity pathways.
Noradrenaline
All major adrenergic receptors are metabotropic GPCRs.
| Receptor | Major locations |
|---|---|
| α1 | Vascular smooth muscle; GI/GU sphincters; iris dilator; CNS |
| α2 | Presynaptic sympathetic nerve terminals; CNS/brainstem; platelets |
| β1 | Heart; juxtaglomerular cells; CNS |
| β2 | Bronchial, vascular and uterine smooth muscle; liver and skeletal muscle |
| β3 | Adipose tissue; bladder detrusor |
Functional roles
- Major transmitter of most postganglionic sympathetic nerves.
- Regulates vascular tone and arterial pressure.
- Modulates cardiac rate and contractility.
- Contributes to metabolic and thermoregulatory sympathetic responses.
- CNS noradrenergic pathways, particularly from the locus coeruleus, regulate arousal, attention and the sleep–wake state.
- Contributes to descending modulation of pain.
Serotonin (5-HT)
5-HT3 is ionotropic; the other major 5-HT receptor families are metabotropic GPCRs.
| Receptor | Type | Major locations |
|---|---|---|
| 5-HT1 | Metabotropic | CNS: raphe, limbic system, hippocampus, cortex and basal ganglia; cerebral vessels |
| 5-HT2 | Metabotropic | CNS; platelets; vascular and GI smooth muscle |
| 5-HT3 | Ionotropic ligand-gated cation channel | Area postrema / CTZ, vagal afferents, enteric nervous system, spinal cord and CNS |
| 5-HT4 | Metabotropic | CNS and enteric nervous system / GIT |
| 5-HT5 | Metabotropic | Predominantly CNS |
| 5-HT6 | Metabotropic | Predominantly CNS |
| 5-HT7 | Metabotropic | CNS, particularly hypothalamic regions; GIT and blood vessels |
Functional roles
- Regulation of mood, anxiety and behaviour.
- Modulation of sleep and arousal.
- Appetite and satiety.
- Pain modulation.
- Nausea and vomiting, particularly via 5-HT3 receptors.
- Gastrointestinal motility and secretion.
- Thermoregulation.
Quick reference
Summary
| Neurotransmitter | Receptor headline | Key physiological role |
|---|---|---|
| ACh | Nicotinic = ionotropic; muscarinic = metabotropic | NMJ, autonomic transmission, cognition/arousal |
| GABA | GABAA ionotropic; GABAB metabotropic | Major CNS inhibition |
| Noradrenaline | α/β receptors all metabotropic | Sympathetic transmission, arousal/attention |
| 5-HT | 5-HT3 ionotropic; others metabotropic | Mood, nausea, GIT, sleep, thermoregulation |
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2026A Q05 | For each neurotransmitter listed below: a) acetylcholine (ACh), b) gamma-aminobutyric acid (GABA), c) noradrenaline (NorAd), d) serotonin (5-HT). Outline the following: i) target receptors, including type and location (15% of marks per neurotransmitter), Downstream receptor mechanisms NOT required. ii) functional role(s) (10% of marks per neurotransmitter). | 38.6% |