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(Science: physiology) A connection between excitable cells, by which an excitation is conveyed from one to the other.
1. Chemical synapse: one in which an action potential causes the exocytosis of neurotransmitter from the presynaptic cell, which diffuses across the synaptic cleft and binds to ligand gated ion channels on the post synaptic cell. These ion channels then affect the resting potential of the post synaptic cell.
2. Electrical synapse: one in which electrical connection is made directly through the cytoplasm, via gap junctions.
3. Rectifying synapse: one in which action potentials can only pass across the synapse in one direction (all chemical and some electrical synapses).
4. Excitatory synapse: one in which the firing of the presynaptic cell increases the probability of firing of the postsynaptic cell.
5. Inhibitory synapse: one in which the firing of the presynaptic cell reduces the probability of firing of the postsynaptic cell.