🎓 Prepared by students from Boğaziçi University

What is Neurotransmission?

Neurotransmission is how neurons communicate with each other and with muscles or glands, using electrical signals (action potentials) inside the neuron and chemical signals (neurotransmitters) to cross the gap between cells at a synapse.

Short answer

Neurotransmission is the process by which an electrical impulse (action potential) travels along a neuron, triggers the release of chemical neurotransmitters at the synapse, and these bind to receptors on the next cell to pass the signal on.

Steps of Synaptic Transmission

1
Action potential arrives
An electrical impulse reaches the axon terminal of the presynaptic neuron.
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2
Calcium influx
Voltage-gated calcium channels open and Ca²⁺ enters the terminal.
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3
Vesicle fusion
Calcium triggers synaptic vesicles to fuse with the presynaptic membrane.
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4
Neurotransmitter release
Neurotransmitter molecules are released into the synaptic cleft by exocytosis.
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5
Receptor binding
Neurotransmitters bind to receptors on the postsynaptic membrane, opening ion channels.
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6
Reuptake or breakdown
Leftover neurotransmitter is reabsorbed or broken down by enzymes, ending the signal.

Step-by-step worked examples

A motor neuron needs to make a muscle contract. Trace the neurotransmission steps at the neuromuscular junction.

An action potential travels down the motor neuron's axon
Calcium enters the axon terminal, triggering vesicle fusion
Acetylcholine (the neurotransmitter) is released into the synaptic cleft
Acetylcholine binds to receptors on the muscle fiber membrane
This opens ion channels, triggering a new electrical signal that causes the muscle to contract

A drug blocks the reuptake of serotonin at the synapse (like an SSRI). Explain the effect on neurotransmission.

Normally, released serotonin is reabsorbed into the presynaptic neuron after signaling
Blocking reuptake means serotonin stays in the synaptic cleft longer
This increases and prolongs serotonin's binding to postsynaptic receptors
Result: serotonin signaling between neurons is enhanced, which is why SSRIs are used to treat depression

A toxin destroys voltage-gated calcium channels at the presynaptic terminal. Predict the effect.

Without functional calcium channels, calcium cannot enter the axon terminal when an action potential arrives
Without calcium influx, synaptic vesicles cannot fuse with the membrane
Result: neurotransmitter cannot be released, and the signal fails to cross the synapse — communication between the two neurons stops

Flashcards

Quick quiz

Q1.What directly triggers the release of neurotransmitters at the synapse?

Correct answer: B. Calcium entering the axon terminal causes synaptic vesicles to fuse and release neurotransmitter.

Q2.Where do neurotransmitters bind after being released?

Correct answer: A. Neurotransmitters cross the synaptic cleft and bind to receptors on the next neuron.

Q3.What is acetylcholine an example of?

Correct answer: B. Acetylcholine is a neurotransmitter used at neuromuscular junctions and elsewhere.

Q4.How is a neurotransmitter signal typically ended?

Correct answer: B. Reuptake or breakdown clears the neurotransmitter, ending the signal.

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Common mistakes

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Thinking electrical signals cross the synaptic gap directly. — Correct: Electrical signals travel within a neuron; a chemical neurotransmitter crosses the gap between neurons.

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Confusing neurons touching directly. — Correct: Neurons don't touch — there is a small gap (synaptic cleft) between them.

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Believing all neurotransmitters are excitatory. — Correct: Some neurotransmitters (like GABA) are inhibitory and reduce the chance of firing.

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Thinking neurotransmitter release doesn't need calcium. — Correct: Calcium influx is essential — it triggers vesicle fusion and release.

FAQ

What is neurotransmission?

Neurotransmission is how a neuron sends a signal — electrically within itself and chemically across the synapse to the next cell.

What is the process (formula) of neurotransmission?

There's no numeric formula, but the sequence is: action potential → calcium influx → vesicle fusion → neurotransmitter release → receptor binding → reuptake/breakdown.

What are examples of neurotransmitters?

Acetylcholine, dopamine, serotonin, and GABA are common neurotransmitters, each with different effects.

How does a nerve signal cross a synapse?

It doesn't cross directly — the electrical signal triggers release of a chemical neurotransmitter, which diffuses across the synaptic cleft and binds receptors on the next neuron.