Introduction of Synaptic Transmission
As we know, synaptic transmission refers to the communication between neurons. Generally, information will be transmitted along the axon in the form of action potentials. And when the action potential is transmitted to the end of the axon, through the synaptic cleft, the information will be transferred to another neuron to continue transmission. There are synaptic vesicles containing neurotransmitters at the ends of axons. Neurotransmitters would be released when the action potential reaches their synaptic vesicles, and then bind to receptor sites on postsynaptic cells to complete the process of synaptic transmission. Chemical synaptic transmission, as well as electrical synaptic transmission, are the two main types of synaptic transmission.
- Chemical Synapse Transmission
Using a sophisticated chemical signaling scheme, chemical synapses convert pre-synaptic action potentials into chemical signals, which are then converted into electrical signals in postsynaptic cells. Once the action potential propagates along the axon and reaches a presynaptic terminal, the voltage-gated calcium channels would be activated, and the resulting influx of calcium ions triggers intercellular signaling. Through diffusion, the neurotransmitter molecules are released into the synaptic cleft and then bind to their specific synaptic receptors to complete the whole chemical synapse transmission.
Fig.1 Basic elements of a chemical synapse with ionotropic receptors.
- Electrical Synapse Transmission
Compared with long-range communication using chemical synapse transmission, neurons can also communicate with other neurons via electrical synapses. That is, when the action potential of the presynaptic neuron reaches the nerve terminal, the action potential of the postsynaptic component is caused by the action of the local currency. Finally, the electrical synapse transmission promotes the function of the synchronized firing of different neurons.
Fig.2 Dynamics of the electric synapse.
According to the different contact sites, synapses can be divided into three types: axo-dendritic synapse, axo-somatic synapse, and axo-axonic synapse. According to the functions, synapses can also be divided into the excitatory synapse and inhibitory synapse.
Classification of Synaptic Receptors
Two types of synaptic receptors exist, the ionotropic receptors bind neurotransmitter molecules and are also ion channels that enable ion flux across the cell membrane to change the electrical state of the postsynaptic neuron directly. The metabotropic receptors also bind neurotransmitter molecules and then modulate ion channels using intracellular biochemical signaling cascades in response to neurotransmitter binding. Among them, ionotropic receptors are ideal for fast synaptic communication, while metabotropic receptors always provide slower and more complex modulation of the electrical state of the postsynaptic neuron.
In the nervous system, the transmitter-gated channels play important roles in synaptic transmission. Some studies have shown that in the enteric nervous system (ENS), G protein-coupled receptors (GPCRs) are essential for the neurogenic control of gastrointestinal (GI) function and have been served as the emerging therapeutic targets. As a global company with extensive scientific expertise, we can provide a series of services and products for neurosciences research. If you are interested in our services and products, please do not hesitate to contact us for more detailed information.