The nervous system is composed of a large number of neurons. These neurons are not connected by protoplasm in structure, only in contact with each other, and the site of contact is called a synapse. Due to the different contact sites, synapses can be mainly divided into three categories: axon cytoplasmic synapses; Axonal dendritic synapse; Axon axon synapse. The axon terminals of a neuron repeatedly branch and swell into cup-shaped or spherical shapes, known as synaptic bodies, which come into contact with the cell bodies or processes of postsynaptic neurons. A presynaptic neuron can form synapses with many postsynaptic neurons, and a postsynaptic neuron can also form synapses with the axon terminals of many presynaptic neurons.