Editing Chemical synapse (section)

== Synaptic plasticity ==
{{Main|Synaptic plasticity}}
Synaptic transmission can be changed by previous activity. These changes are called synaptic plasticity and may result in either a decrease in the efficacy of the synapse, called depression,  or an increase in efficacy, called potentiation. These changes can either be long-term or short-term. Forms of [[Synaptic plasticity#Short-term plasticity|short-term plasticity]] include [[synaptic fatigue]] or depression and [[Synaptic plasticity#Synaptic enhancement|synaptic augmentation]]. Forms of [[Synaptic plasticity#Long-term plasticity|long-term plasticity]] include [[long-term depression]] and [[long-term potentiation]]. Synaptic plasticity can be either homosynaptic (occurring at a single synapse) or heterosynaptic (occurring at multiple synapses).

===Homosynaptic plasticity=== <!--Homotropic modulation redirects here-->
{{Main|Homosynaptic plasticity}}
[[Homosynaptic plasticity]] (or also homotropic modulation) is a change in the synaptic strength that results from the history of activity at a particular synapse.  This can result from changes in presynaptic calcium as well as feedback onto presynaptic receptors, i.e. a form of [[autocrine signaling]]. Homosynaptic plasticity can affect the number and replenishment rate of vesicles or it can affect the relationship between calcium and vesicle release. Homosynaptic plasticity can also be postsynaptic in nature. It can result in either an increase or decrease in synaptic strength.

One example is neurons of the [[sympathetic nervous system]] (SNS), which release [[noradrenaline]], which, besides affecting postsynaptic receptors, also affects presynaptic [[α2-adrenergic receptors]], inhibiting further release of noradrenaline.<ref name=Rang>{{cite book |author1=Rang, H.P. |author2=Dale, M.M. |author3=Ritter, J.M. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |page=129 |isbn=978-0-443-07145-4 |edition=5th}}</ref> This effect is utilized with [[clonidine]] to perform inhibitory effects on the SNS.

===Heterosynaptic plasticity=== <!--Heterotropic modulation redirects here-->
{{Main|Heterosynaptic plasticity}}
[[Heterosynaptic plasticity]] (or also heterotropic modulation) is a change in synaptic strength that results from the activity of other neurons. Again, the plasticity can alter the number of vesicles or their replenishment rate or the relationship between calcium and vesicle release.  Additionally, it could directly affect calcium influx.  Heterosynaptic plasticity can also be postsynaptic in nature, affecting receptor sensitivity.

One example is again neurons of the [[sympathetic nervous system]], which release [[noradrenaline]], which, in addition, generates an inhibitory effect on presynaptic terminals of neurons of the [[parasympathetic nervous system]].<ref name=Rang/>