Instead, a space called the synaptic cleft exists between the presynaptic terminal and the postsynaptic membrane. ChemicalĬhemical synapses outnumber electrical synapses in the fully developed nervous systemĬhemical synapses are the primary synapse type in the developed nervous system and do not form physical connections between the pre- and postsynaptic neurons. ‘Electrical Synapse – Small Molecules’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.

Gap junctions are large enough to allow the flow of small cellular molecules like ATP or second messengers. Electrical synapses play an important role in the development of the nervous system but are also present throughout the developed nervous system, although in much smaller numbers that chemical synapses.Īnimation 8.3. The response in the postsynaptic cell is almost immediate, with little to no delay between signaling in the pre- and postsynaptic neurons. The gap junctions form pores that allow ions to flow between neurons, so as an action potential propagates in the presynaptic neuron, the influx of sodium can move directly into the postsynaptic neuron and depolarize the cell. Cell membrane proteins called connexons form gap junctions between the neurons. ElectricalĮlectrical synapses outnumber chemical synapses in the developing nervous systemĮlectrical synapses are a physical connection between two neurons. There are two types of synapses: electrical and chemical. ‘Synapse’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. The terminal of a presynaptic neuron comes into close contact with a postsynaptic cell at the synapse. At the synapse, the terminal of a presynaptic cell comes into close contact with the cell membrane of a postsynaptic neuron. The post-synaptic cell will only send the message along if it gets enough excitatory input to depolarize across the threshold, and open the voltage-gated ion channels in its axon.For the nervous system to function, neurons must be able to communicate with each other, and they do this through structures called synapses. There might even be competition among the neurons, with a single post-synaptic neuron receiving glutamate from one pre-synaptic neuron and GABA from its neighbor. This is why the brain uses neuron networks to send many signals to a single cell, or why a neuron may have to fire a couple times before it can pass the message along. Most of the time, all the vesicles released from an action potential aren’t enough to trigger an action potential in the following cell. However, a single vesicle of neurotransmitter isn’t enough to depolarize the cell body. If the neurotransmitter is inhibitory, it will hyperpolarize the cell body. If the neurotransmitter is excitatory, the influx of positive ions will depolarize (bring closer to zero) the cell body. Each vesicle packet released from the pre-synaptic neuron will contain a set amount of neurotransmitters, which will then bind to some of the receptors on the post-synaptic cell.

Space between dendrite and axon