Synaptic cleft

The narrow extracellular gap between a presynaptic cell and a postsynaptic cell at a chemical synapse. Neurotransmitters cross it to carry signals between the cells.

Synaptic vesicle: A membrane-bound compartment that stores neurotransmitters and releases them when it fuses with a cell membrane. Vesicles release neurotransmitters into the cleft by fusing with the presynaptic membrane.
Chemical synapse: A junction where one cell communicates with another by releasing chemical messengers. The synaptic cleft is the extracellular space at the center of this junction.
Myasthenia gravis: An autoimmune disorder in which antibodies impair communication at the neuromuscular junction. Antibodies commonly reduce postsynaptic acetylcholine receptors across the cleft.
Electrical synapse: A cell junction that passes electrical current directly between cells through gap junction channels. It transmits signals without neurotransmitter diffusion across an extracellular cleft.
Neurotransmitter: A chemical messenger released by a neuron that alters the activity of a target cell. Neurotransmitters diffuse through the cleft to reach postsynaptic receptors.
Presynaptic terminal: The specialized ending of a neuron that releases neurotransmitters at a chemical synapse. Its membrane forms one boundary of the cleft and hosts release machinery.
Botulinum toxin: A bacterial neurotoxin that blocks acetylcholine release at cholinergic nerve endings. It prevents transmitter from entering the cleft at neuromuscular junctions.
Gap junction: A channel-forming intercellular junction that allows ions and small molecules to pass between neighboring cells. Unlike a chemical synapse, it provides a direct cytoplasmic route between cells.
Postsynaptic density: A protein-rich specialization on the postsynaptic membrane that organizes receptors and signaling proteins. It concentrates receptors opposite release sites across the cleft.
Postsynaptic membrane: The target-cell membrane at a synapse, containing receptors and associated signaling proteins. It forms the cleft’s opposite boundary and detects released messengers.

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