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Difference between revisions of "Synapse"

 
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'''''German''': Synapse''   
 
'''''German''': Synapse''   
 
   
 
   
===Definition===  
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==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).  
 
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===  
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==Structure==
 
A synapse consists of 3 elements:
 
A synapse consists of 3 elements:
 
*'''Presynapse''' or presynaptic part: The part that elicits the stimulus.
 
*'''Presynapse''' or presynaptic part: The part that elicits the stimulus.
 
*'''Postsynapse''' or postsynaptic part: The part that receives the stimulus.  
 
*'''Postsynapse''' or postsynaptic part: The part that receives the stimulus.  
*'''Synaptic cleft''': The space between the two structures. ClassificationSynapses are classified according to neurotransmission and kinds of stimulus: According to neurotransmissionElectrical synapseThe electrical synapse or gap junction transmits the impulse through very close cell contact via ion channels 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 synapseIn the chemical synapse, the presynapsis releases neurotransmitters from vesicles to transmit the impulse. This process, which makes necessary a complex interaction of various proteins, 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 impulseStimulating synapseStimulating synapses create an EPSP (excitatory postsynaptic potential) in the postsynaptic cell, which can trigger a depolarization. Inhibiting synapseInhibiting synapses lead to a IPSP (inhibitory postsynaptic potential) in the postsynaptic cell, which suppresses a depolarisation. According to siteThree 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
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*'''Synaptic cleft''': The space between the two structures.  
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==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 channels 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).  
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===Chemical synapse===
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In the chemical synapse, the presynapsis releases [[neurotransmitters]] from [[vesicles]] to transmit the impulse. This process, which makes necessary a complex interaction of various proteins, 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 [[EPSP]] (excitatory postsynaptic potential) in the postsynaptic cell, which can trigger a [[depolarization]].  
 +
===Inhibiting synapse===
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Inhibiting synapses lead to a [[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]])
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*''Axo-dendritic synapses'': connection between axon and [[dendrite tree]]
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*''Axo-axonic synapses'': connection between two axons

Revision as of 19:00, 6 October 2005

German: Synapse

1 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).

2 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.

3 Classification

Synapses are classified according to neurotransmission and kinds of stimulus:

4 According to neurotransmission

4.1 Electrical synapse

The electrical synapse or gap junction transmits the impulse through very close cell contact via ion channels 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).

4.2 Chemical synapse

In the chemical synapse, the presynapsis releases neurotransmitters from vesicles to transmit the impulse. This process, which makes necessary a complex interaction of various proteins, 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.

4.3 According to the kind of impulse

4.4 Stimulating synapse

Stimulating synapses create an EPSP (excitatory postsynaptic potential) in the postsynaptic cell, which can trigger a depolarization.

4.5 Inhibiting synapse

Inhibiting synapses lead to a IPSP (inhibitory postsynaptic potential) in the postsynaptic cell, which suppresses a depolarisation.

4.6 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

Specialties: Anatomy

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