Editing Dendrite (section)

== Structure and function ==
[[File:CA1 pyramidal cells with synapses.png|thumb|519x519px|The extensive dendritic tree of two hippocampal pyramidal neurons (magenta) with all incoming synapses genetically labeled (green spots).<ref>{{Cite journal |last1=Perez-Alvarez |first1=Alberto |last2=Fearey |first2=Brenna C. |last3=O’Toole |first3=Ryan J. |last4=Yang |first4=Wei |last5=Arganda-Carreras |first5=Ignacio |last6=Lamothe-Molina |first6=Paul J. |last7=Moeyaert |first7=Benjamien |last8=Mohr |first8=Manuel A. |last9=Panzera |first9=Lauren C. |last10=Schulze |first10=Christian |last11=Schreiter |first11=Eric R. |last12=Wiegert |first12=J. Simon |last13=Gee |first13=Christine E. |last14=Hoppa |first14=Michael B. |last15=Oertner |first15=Thomas G. |date=2020-05-18 |title=Freeze-frame imaging of synaptic activity using SynTagMA |journal=Nature Communications |language=en |volume=11 |issue=1 |page=2464 |doi=10.1038/s41467-020-16315-4 |issn=2041-1723 |pmc=7235013 |pmid=32424147|bibcode=2020NatCo..11.2464P }}</ref>]]
Dendrites are one of two types of [[cytoplasmic process]]es that extrude from the cell body of a [[neuron]], the other type being an [[axon]]. Axons can be distinguished from dendrites by several features including shape, length, and function. Dendrites often taper off in shape and are shorter, while axons tend to maintain a constant radius and can be very long. Typically, axons transmit electrochemical signals and dendrites receive the electrochemical signals, although some types of neurons in certain species lack specialized axons and transmit signals via their dendrites.<ref name=Yau /> Dendrites provide an enlarged surface area to receive signals from [[Axon terminal|axon terminals]] of other neurons.<ref name="Alberts 2009">{{cite book| vauthors = Alberts B |title=Essential Cell Biology|date=2009|publisher=Garland Science|location=New York|isbn=978-0-8153-4129-1|edition=3rd}}</ref>  The dendrite of a large [[pyramidal cell]] receives signals from about 30,000 presynaptic neurons.<ref>{{Cite journal |last1=Eyal |first1=Guy |last2=Verhoog |first2=Matthijs B. |last3=Testa-Silva |first3=Guilherme |last4=Deitcher |first4=Yair |last5=Benavides-Piccione |first5=Ruth |last6=DeFelipe |first6=Javier |last7=de Kock |first7=Christiaan P. J. |last8=Mansvelder |first8=Huibert D. |last9=Segev |first9=Idan |date=2018-06-29 |title=Human Cortical Pyramidal Neurons: From Spines to Spikes via Models |journal=Frontiers in Cellular Neuroscience |volume=12 |page=181 |doi=10.3389/fncel.2018.00181 |issn=1662-5102 |pmc=6034553 |pmid=30008663 |doi-access=free }}</ref> [[Excitatory synapse|Excitatory synapses]] terminate on [[Dendritic spine|dendritic spines]], tiny protrusions from the dendrite with a high density of [[Neurotransmitter receptor|neurotransmitter receptors]]. Most [[inhibitory synapses]] directly contact the dendritic shaft.

Synaptic activity causes local changes in the electrical potential across the plasma membrane of the dendrite. This change in membrane potential will passively spread along the dendrite, but becomes weaker with distance without an [[action potential]]. To generate an action potential, many excitatory synapses have to be active at the same time, leading to strong depolarization of the dendrite and the cell body ([[Soma (biology)|soma]]). The action potential, which typically starts at the [[axon hillock]], propagates down the length of the axon to the axon terminals where it triggers the release of neurotransmitters, but also backwards into the dendrite (retrograde propagation), providing an important signal for [[spike-timing-dependent plasticity]] (STDP).<ref name="Alberts 2009" /> 

Most [[synapse]]s are axodendritic, involving an axon signaling to a dendrite. There are also [[dendrodendritic synapse]]s, signaling from one dendrite to another.<ref name="Carlson 2013">{{cite book| vauthors = Carlson NR |title=Physiology of Behavior|date=2013|publisher=Pearson|location=Boston|isbn=978-0-205-23939-9|edition=11th}}</ref> An [[autapse]] is a synapse in which the axon of one neuron transmits signals to its own dendrite.

The general structure of the dendrite is used to classify neurons into [[Multipolar neuron|multipolar]], [[Bipolar neuron|bipolar]] and [[Unipolar neuron|unipolar]] types. Multipolar neurons are composed of one axon and many dendritic trees. [[Pyramidal cells]] are multipolar cortical neurons with pyramid-shaped cell bodies and large dendrites that extend towards the surface of the cortex ([[apical dendrite]]). Bipolar neurons have two main dendrites at opposing ends of the cell body. Many inhibitory neurons have this morphology.  Unipolar neurons, typical for insects, have a stalk that extends from the cell body that separates into two branches with one containing the dendrites and the other with the terminal buttons. In vertebrates, sensory neurons detecting touch or temperature are unipolar.<ref name="Carlson 2013" /><ref>{{cite book| vauthors = Pinel JP |title=Biopsychology|date=2011|publisher=Allyn & Bacon|location=Boston|isbn=978-0-205-83256-9|edition=8th}}</ref><ref>{{cite journal | vauthors = Jan YN, Jan LY | title = Branching out: mechanisms of dendritic arborization | journal = Nature Reviews. Neuroscience | volume = 11 | issue = 5 | pages = 316–328 | date = May 2010 | pmid = 20404840 | pmc = 3079328 | doi = 10.1038/nrn2836 }}</ref> Dendritic branching can be extensive and in some cases is sufficient to receive as many as 100,000 inputs to a single neuron.<ref name="Alberts 2009" />