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Diagram of a chemical synaptic connection. In the nervous system, a synapse [1] is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending on the mechanism of signal transmission between neurons.
The number of synapses in the human cerebral cortex has separately been estimated at 0.15 quadrillion (150 trillion) [3] The word "synapse" was introduced by Sir Charles Scott Sherrington in 1897. [4] Chemical synapses are not the only type of biological synapse: electrical and immunological synapses also exist. Without a qualifier, however ...
An excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell. Neurons form networks through which nerve impulses travels, each neuron often making numerous connections with other cells of neurons.
In a parallel after-discharge circuit, a neuron inputs to several chains of neurons. Each chain is made up of a different number of neurons but their signals converge onto one output neuron. Each synapse in the circuit acts to delay the signal by about 0.5 msec, so that the more synapses there are, the longer is the delay to the output neuron.
An electrical synapse, or gap junction, is a mechanical and electrically conductive synapse, a functional junction between two neighboring neurons. The synapse is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction .
Synapses may be electrical or chemical. Electrical synapses make direct electrical connections between neurons, [41] but chemical synapses are much more common, and much more diverse in function. [42] At a chemical synapse, the cell that sends signals is called presynaptic, and the cell that receives signals is called postsynaptic.
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Once at the synapse, synaptic vesicles are loaded with a neurotransmitter. Loading of transmitter is an active process requiring a neurotransmitter transporter and a proton pump ATPase that provides an electrochemical gradient. These transporters are selective for different classes of transmitters.