What is a chemical synapse?

A chemical synapse is a tiny junction (about 20-40 nanometres wide) between two neurons, where the signal is carried across by chemical messengers called neurotransmitters. The neuron before the gap is called pre-synaptic; the one after is called post-synaptic. Most synapses in the human brain are chemical synapses.

What triggers neurotransmitter release at a synapse?

When an action potential reaches the axon terminal, it opens voltage-gated calcium (Ca²⁺) channels in the pre-synaptic membrane. Ca²⁺ rushes into the terminal, which causes synaptic vesicles to fuse with the membrane and release their stored neurotransmitter into the cleft. Without Ca²⁺ influx, no neurotransmitter is released.

What are synaptic vesicles?

Synaptic vesicles are small membrane-bound sacs in the axon terminal, each containing roughly 10,000 neurotransmitter molecules. They cluster near the pre-synaptic membrane in regions called active zones. When triggered by Ca²⁺ influx, they fuse with the membrane and release their contents through exocytosis.

How do neurotransmitters affect the post-synaptic neuron?

After being released into the cleft, neurotransmitters diffuse across and bind to specific receptor proteins on the post-synaptic membrane. Excitatory neurotransmitters (like acetylcholine, glutamate) open channels that depolarise the post-synaptic neuron, encouraging a new action potential. Inhibitory neurotransmitters (like GABA) hyperpolarise it, making firing less likely.

Which common neurotransmitters does NEET test?

The most frequently tested are acetylcholine (excitatory, neuromuscular junction), GABA (main inhibitory neurotransmitter), dopamine (reward and motor control), serotonin (mood), noradrenaline (alertness), and glutamate (main excitatory neurotransmitter in the brain). NCERT explicitly mentions acetylcholine for the neuromuscular junction example.

How fast does synaptic transmission happen?

The entire sequence — action potential arrival, Ca²⁺ influx, vesicle fusion, neurotransmitter diffusion across the cleft, and receptor binding — takes only about 0.5 to 1 millisecond. The narrow width of the synaptic cleft (20-40 nm) makes diffusion almost instantaneous on a biological timescale.

Is synaptic transmission a NEET topic?

Yes. Synaptic transmission is part of the Class 11 chapter 'Neural Control and Coordination' and appears in NEET every year. Common question patterns include identifying the trigger for vesicle fusion (Ca²⁺), the role of acetylcholine at the neuromuscular junction, and distinguishing electrical from chemical synapses.

Human PhysiologyMediumNEET: 2-3 Q3D

Synaptic Transmission — Ca²⁺, Vesicles & Release

Neural Control and Coordination

Step inside a synaptic terminal. Drag the firing-stage slider through Rest, Ca²⁺ Influx, and Release. Watch vesicles dock, fuse, and pour neurotransmitters across the cleft to light up the post-synaptic receptors.

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Synaptic Transmission — Ca²⁺, Vesicles & Release

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How to use this lab