Synapses are narrow junctions where neurotransmitters carry signals from presynaptic neurons to receptor-bearing postsynaptic membranes, linking cellular mechanisms to rapid communication in nervous systems.
Coverage 2013–2024 · Updated 15 Jul 2026
A synapse is a junction where a presynaptic cell communicates with a postsynaptic cell, usually through neurotransmitter release.
The synaptic cleft separates membranes, creating a one-way delay in chemical synapses. Receptors on the postsynaptic membrane convert transmitter binding into ion-flow or intracellular effects. The synapse is a junction, so the signal must be converted before it can cross to the next cell.
Describe a chemical synapse:
An action potential at a motor neuron terminal releases transmitter that binds receptors on a muscle fibre.
A synapse is not simply a physical gap; receptor type and transmitter removal determine the response.
This objective is assessed through structured response, commonly using Explain / Describe / State.
Explain / Describe / State / Identify / Distinguish / Suggest
Build the answer around this relationship: Synapses transmit signals chemically between neurons.
Representative question
Distinguish between the presynaptic and postsynaptic membranes by giving two differences.
Neurons carry electrical impulses in the nervous system; motor, sensory, and relay neurons differ in axon, dendrite, and cell body arrangement. Sodium-potassium pumps use ATP to move 3 Na+ out and 2 K+ in; ion gradients make the resting axon polarized at about -70 mV. A nerve impulse is a propagated action potential along a nerve fibre; stimulus-triggered sodium influx reverses membrane polarity. Larger axon diameter lowers resistance and increases impulse speed; myelin sheaths and nodes of Ranvier enable faster saltatory conduction. Synapses connect neurons to neurons, muscles, or glands; chemical synapses transmit one way across a narrow synaptic cleft. Action potentials open voltage-gated Ca2+ channels in presynaptic terminals; Ca2+ causes vesicle fusion and neurotransmitter exocytosis into the cleft. Neurotransmitters diffuse and bind receptors on the postsynaptic membrane; EPSPs depolarize the membrane and make threshold more likely.
