Synaptic cleft

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Neurons are the basic building blocks of the nervous system.

The synaptic cleft is a junction or small gap at which neurons communicate with each other. The synapse is a specialized connection between cells that enables communication between neurons within the central nervous system (CNS) or between a neuron and an effector cell (such as another neuron, muscle cell, or gland cell) in the peripheral nervous system (PNS). Action potentials are fired from one neuron - the presynaptic neuron- to the receiving neuron - the postsynaptic neuron. There are two types of synapse: the electrical (gap junctions) and the chemical . 

The electrical synapse has a synaptic cleft width of 2-4nm and facilitates the transfer of ions or small molecules between adjacent cells by allowing them to pass through tiny channels present in the cell membranes of both cells. These synapses are fewer in number in mammals in comparison to chemical synapses. 

The chemical synapse has a synaptic cleft width of 20-30nm and is the site where cells release two types of messenger molecules. These are neurotransmitters and neuromodulators and they are carried in synaptic vesicles. They are released from the axon terminal and bind to receptors on the membrane of the neighbouring or effector cell, triggering the intended outcome.