Dendrite structure and function8/22/2023 ![]() Beyond their role as conducting cables, dendrites of many neuron types contain a rich repertoire of ionic mechanisms that allow them to perform complex nonlinear computations. Since the majority of synaptic connections reside in dendrites, they provide the primary substrate for inter-neuronal communication. ‘Chemical Synapse Types’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.Dendrites are thin processes extending from the cell bodies of neurons. C) Axoaxonic synapses occur when the presynaptic terminal makes a synaptic connection with the axon of a postsynaptic neuron. B) Axosomatic synapses occur when the presynaptic terminal makes a synaptic connection with the cell body of a postsynaptic neuron. A) Axodendritic synapses occur when the presynaptic terminal makes a synaptic connection with the dendrite of a postsynaptic neuron. But synapses can also be located between the terminal and the cell body of the postsynaptic cell, called axosomatic, or even between the terminal and the axon of the postsynaptic cell, called axoaxonic. Synapse LocationĪs we discuss synaptic transmission, we will focus mainly on axodendritic synapses, in which the presynaptic terminal synapses on the dendrites of the postsynaptic cell. ‘Chemical Synapse – Neurotransmitter Release’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. The transmitters then act on neurotransmitter receptors in the postsynaptic membrane. An action potential causes release of neurotransmitters from the presynaptic terminal into the synaptic cleft. The structure and function of chemical synapses make them slower than electrical synapses and permit signaling in only one direction.Īnimation 8.4. ‘Chemical Synapse’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.Īt a chemical synapse, the depolarization of an action potential reaching the presynaptic terminal causes release of neurotransmitters, which act on specialized receptors located in the cell membrane of the postsynaptic neuron. Neurotransmitters are stored in the presynaptic cell, and the postsynaptic cell has neurotransmitter receptors in the membrane. The presynaptic terminal and the postsynaptic membrane are separated by the synaptic cleft. A chemical synapse does not make direct contact between the two neurons. 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. For the nervous system to function, neurons must be able to communicate with each other, and they do this through structures called synapses. ![]()
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