Neurotransmitters Tournament
Two onboarding diagrams orient you in the chemical synapse. Then eight MCAT-DoK quiz rounds: synaptotagmin as the Ca2+ sensor, botulinum vs. tetanus toxin cleaving SNAREs, the full vesicle cycle, neurotransmitter-to-disease pairings from Parkinson to myasthenia gravis, SNARE stoichiometry, ionotropic vs. metabotropic receptors, DAT/SERT/NET vs. MAO, and organophosphate poisoning.
Where the Neurotransmitter release cycle fits in Transmission across chemical synapses
A chemical synapse is a signal converter: the electrical action potential that races down the axon is translated into a chemical message, then back into an electrical response in the next cell. Ca2+ is the hinge of that conversion, and the highlighted release-cycle panel is exactly that loop - Ca2+ entry, synaptotagmin sensing, SNARE-driven vesicle fusion, transmitter clearance, and endocytic refill of the vesicle pool. Click the highlighted Neurotransmitter release cycle panel to enter the tournament.
Click the highlighted Neurotransmitter release cycle box to continue.
What this tournament tests
Each task maps to a distinct MCAT cognitive demand. The first two orient you in the broader topology; the next eight test the high-yield mechanism, regulation, sequence and quantitative reasoning that consistently appear on test day.
The Bigger Picture
Anchor the neurotransmitter release cycle inside transmission across chemical synapses on the live Reactome map.
Whole-Pathway Overview
Pan and zoom the curated WikiPathways synaptic vesicle cycle figure before you start answering.
Fill in the Blank
Recall synaptotagmin as the vesicular Ca2+ sensor that triggers SNARE-mediated fusion.
Disruptor
Explain why botulinum toxin causes flaccid paralysis while tetanus toxin causes spastic paralysis.
Sequence Ordering
Trace spike -> Ca2+ influx -> synaptotagmin -> SNARE fusion -> receptor binding -> clearance -> endocytic refill.
Match the Pairs
Pair dopamine, serotonin, acetylcholine, GABA, glutamate, norepinephrine, and glycine with their clinical hooks.
Numeric Input
Recall that three core SNARE proteins form the vesicle fusion complex.
Select All That Apply
Distinguish ligand-gated channels (nicotinic, GABA_A, NMDA) from GPCRs (muscarinic, GABA_B, adrenergic).
Odd One Out
Separate the reuptake transporters DAT, SERT, and NET from the degradative enzyme MAO-A.
Organophosphate Disruptor
Predict the muscarinic and nicotinic consequences of irreversible acetylcholinesterase inhibition.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
Neurotransmission in 60 seconds
An action potential reaching the terminal opens voltage-gated Ca2+ channels, and the Ca2+ that enters is the actual trigger for release: it binds synaptotagmin on docked vesicles, which drives full zippering of the SNARE complex - synaptobrevin (VAMP) on the vesicle plus syntaxin-1 and SNAP-25 on the plasma membrane. Transmitter is exocytosed into the 20 to 40 nm cleft, and clathrin-mediated endocytosis then retrieves and refills the vesicle. Electrical -> chemical -> electrical, with a synaptic delay of roughly 0.5 ms and strictly one-way transmission.
Postsynaptic receptors come in two flavors. Ionotropic receptors are ligand-gated ion channels and act in milliseconds: nicotinic acetylcholine and AMPA/NMDA glutamate receptors are excitatory, while GABA_A and glycine are Cl- channels that hyperpolarize the cell (an IPSP). Metabotropic receptors are GPCRs - muscarinic, adrenergic, dopaminergic, GABA_B - and trade speed for amplification and duration. The NMDA receptor needs glutamate, glycine, and depolarization to expel Mg2+, making it the coincidence detector behind long-term potentiation and behind excitotoxic Ca2+ death in stroke.
Clearance determines how long the signal lasts. Acetylcholine is destroyed in the cleft by acetylcholinesterase; monoamines are recaptured by DAT, SERT, and NET and then degraded by MAO and COMT. That single distinction generates most of the pharmacology: SSRIs block SERT, cocaine blocks all three monoamine transporters, amphetamines reverse them and dump vesicular stores, and MAO inhibitors raise transmitter levels but risk a tyramine hypertensive crisis.
High-yield disease hooks: Parkinson disease is nigrostriatal dopamine loss (levodopa/carbidopa, MAO-B and COMT inhibitors) while the dopamine hypothesis of schizophrenia motivates D2 blockade. Botulinum toxin cleaves peripheral cholinergic SNAREs (flaccid paralysis) and tetanus toxin cleaves them in spinal inhibitory interneurons (spastic paralysis). Myasthenia gravis is postsynaptic nicotinic receptor autoantibodies - weakness worsening with use, improved by pyridostigmine - whereas Lambert-Eaton targets presynaptic Ca2+ channels.
FAQ
Why is Ca2+ the trigger for neurotransmitter release?
Ca2+ is kept extremely low inside the terminal, so opening voltage-gated Ca2+ channels creates a steep, fast, highly localized influx right at the active zone. Synaptotagmin on the vesicle binds that Ca2+ and pushes the partially assembled SNARE complex to complete fusion. Remove extracellular Ca2+ and the action potential still arrives at the terminal, but no transmitter is released - which is why presynaptic Ca2+ channel autoantibodies in Lambert-Eaton syndrome cause weakness.
What is the fastest way to tell ionotropic from metabotropic receptors?
Ask whether the transmitter opens a channel itself. Ionotropic receptors ARE ion channels, so responses are fast (milliseconds) and brief: nicotinic acetylcholine, AMPA and NMDA, GABA_A, glycine, 5-HT3. Metabotropic receptors are GPCRs that work through G proteins and second messengers, so responses are slower but amplified and longer: all muscarinic and adrenergic receptors, dopamine D1 to D5, GABA_B, and most serotonin receptors.
How do botulinum and tetanus toxin differ if both cleave SNAREs?
The molecular lesion is the same - blocked vesicle fusion - but the target neuron differs. Botulinum toxin acts peripherally on cholinergic terminals, so acetylcholine release at the neuromuscular junction fails and the patient becomes flaccid, with descending weakness and anticholinergic features. Tetanus toxin travels retrogradely to spinal inhibitory interneurons and blocks glycine and GABA release, so motor neurons lose inhibition and the patient becomes spastic, with trismus and opisthotonus.
Why do acetylcholinesterase inhibitors have such dramatic effects?
Acetylcholine is the transmitter cleared by enzymatic destruction rather than reuptake, so acetylcholinesterase is the only brake on its action. Block it and acetylcholine accumulates at every cholinergic synapse: muscarinic overload gives the DUMBBELLS toxidrome, and nicotinic overload at the neuromuscular junction gives fasciculations then depolarizing blockade. Organophosphate poisoning is treated with atropine plus pralidoxime, while low-dose reversible inhibitors such as pyridostigmine treat myasthenia gravis.
Do I need an account to play?
No. The tournament is fully public. You get a randomized handle and your score posts to the public leaderboard at the bottom of this page.
Keep going
The electrical signal that arrives at the terminal - resting potential, Nav gating, refractory periods, and saltatory conduction.
How metabotropic receptors actually work - G-protein subunits, cAMP and IP3 second messengers, and signal amplification.
Overview diagram: Reactome Pathway R-HSA-112315, licensed CC BY 4.0.