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'''''German''': Synapse''  	 
 
==Definition==
A '''synapse''' is a contact point between two [[neurons]], or between a neuron and a [[muscle cell]], which serves the [[transmission of stimuli]]. The term synapse was coined by Sir Charles Sherrington (British physiologist; 1857-1952). 

==Structure==
A synapse consists of 3 elements: 	
*'''Presynapse''' or presynaptic part: The part that elicits the stimulus. 	
*'''Postsynapse''' or postsynaptic part: The part that receives the stimulus. 
*'''Synaptic cleft''': The space between the two structures. 

==Classification==
Synapses are classified according to neurotransmission and kinds of stimulus: 
==According to neurotransmission==

===Electrical synapse===
The electrical synapse or [[gap junction]] transmits the impulse through very close cell contact via [[ion channel]]s directly from nerve cell to nerve cell. The synaptic cleft measures only about 3.5 nm. Electrical synapses work without delay. The neurotransmission is possible [[bidirectionally]]. They mainly occur where a rapid stimulus transmission is necessary (e.g. [[lid reflex]]). 
===Chemical synapse===
In the chemical synapse, the presynapse releases [[neurotransmitters]] from [[vesicles]] to transmit the impulse. This process, which makes necessary a complex interaction of various [[protein]]s, is also called [[exocytosis]]. The neurotransmitters [[diffuse]] through the synaptic cleft and bind to suitable [[receptors]] of the postsynapse. These receptors are either [[ionotropic]] or [[metabotropic]]. The synaptic cleft is wider than in the gap junctions and measures approx. 20-40 nm. Chemical synapses act with a slight time delay (about 1 millisecond). The neurotransmission is possible only [[unidirectionally]]. 

===According to the kind of impulse===


===Stimulating synapse===
Stimulating synapses create an [[excitatory postsynaptic potential|EPSP]] ([[excitatory postsynaptic potential]]) in the postsynaptic cell, which can trigger a [[depolarization]]. 
===Inhibiting synapse===
Inhibiting synapses lead to a [[inhibitory postsynaptic potential)|IPSP]] ([[inhibitory postsynaptic potential]]) in the postsynaptic cell, which suppresses a depolarisation. 
===According to site===
Three types of synapses can be distinguished according to their exact contact point:	

*''Axo-somatic synapses'': connection between [[axon]] and [[cytosome]] ([[soma]]) 	
*''Axo-dendritic synapses'': connection between axon and [[dendrite tree]] 	
*''Axo-axonic synapses'': connection between two axons
[[Specialty:Anatomy]]
[[Tag:Neuroanatomy]]
[[Tag:Neuron]]

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