Excitatory Synapse

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    Excitatory synapse

    From Wikipedia, the free encyclopedia

    A diagram of a typical central nervous system synapse. The spheres located in the upper neuron

    contain neurotransmitters that fuse with the presynaptic membrane and release neurotransmitters

    into the synaptic cleft. These neurotransmitters bind to receptors located on the postsynaptic

    membrane of the lower neuron, and, in the case of an excitatory synapse, may lead to a

    depolarization of the postsynaptic cell.

    An excitatory synapse is a synapse in which an action potentialin a presynaptic neuron increases

    the probability of an action potential occurring in a postsynaptic cell. Neurons form networks

    through which nerve impulses travel, each neuron often making numerous connections withother cells. These electrical signals may be excitatory or inhibitory, and, if the total of excitatory

    influences exceeds that of the inhibitory influences, the neuron will fire, that is, it will generate

    a new action potential at itsaxon hillock, thus transmitting the information to yet another cell.[1]

    This phenomenon is known as an excitatory postsynaptic potential (EPSP). It may occur via

    direct contact between cells (i.e., via gap junctions), as in an electrical synapse, but most

    commonly occurs via the vesicularrelease ofneurotransmitters from the presynaptic axonterminal into the synaptic cleft, as in a chemical synapse.[2]

    The excitatory neurotransmitters, the most common of which is glutamate, then migrate via

    diffusion to thedendritic spine of the postsynaptic neuron and bind a specific transmembrane

    receptorprotein that triggers thedepolarizationof that cell.[1] Depolarization, a deviation from a

    neurons resting membrane potentialtowards its threshold potential, increases the likelihood ofan action potential and normally occurs with the influx of positively chargedsodium (Na+) ions

    into the postsynaptic cell through ion channelsactivated by neurotransmitter binding.

    Contents

    [hide]

    1 Chemical vs electrical synapses 2 Synaptic transmission

    3 Responses of the postsynaptic neuron

    4 Types of excitatory neurotransmitters

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    o 4.1 Acetylcholine

    o 4.2 Glutamate

    o 4.3 Catecholamines

    o 4.4 Serotonin

    o 4.5 Histamine

    5 Diseaseo 5.1 Excitotoxicity

    5.1.1 Pathophysiology 5.1.2 Treatment

    o 5.2 Related neurodegenerative diseases

    6 See also

    7 References

    [edit] Chemical vs electrical synapses

    Animation showing the function of a chemical synapse.There are two different kinds of synapses present within the human brain: chemical and

    electrical. Chemical synapses are by far the most prevalent and are the main playerinvolved in excitatory synapses. Electrical synapses, the minority, allow direct, passiveflow of electrical current through special intercellular connections called gap junctions. [3]

    These gap junctions allow for virtually instantaneous transmission of electrical signals

    through direct passive flow of ions between neurons (transmission can be bidirectional).The main goal of electrical synapses is to synchronize electrical activity among

    populations of neurons[3]. The first electrical synapse was discovered in acrayfish

    nervous system.[3]

    Chemical synaptic transmission is the transfer of neurotransmitters orneuropeptidesfrom

    a presynaptic axon to a postsynaptic axon. [3] Unlike an electrical synapse, the chemical

    synapses are separated by a space called the synaptic cleft, typically measured between

    15 and 25 nm. Transmission of an excitatory signal involves several steps outlined below.

    [edit] Synaptic transmission

    1. In neurons that are involved in chemical synaptic transmission, neurotransmitters are

    synthesized either in the neuronal cell body, or within the presynaptic terminal,

    depending on the type of neurotransmitter being synthesized and the location of enzymes

    http://en.wikipedia.org/wiki/Excitatory_synapse#Acetylcholinehttp://en.wikipedia.org/wiki/Excitatory_synapse#Glutamatehttp://en.wikipedia.org/wiki/Excitatory_synapse#Catecholamineshttp://en.wikipedia.org/wiki/Excitatory_synapse#Serotoninhttp://en.wikipedia.org/wiki/Excitatory_synapse#Histaminehttp://en.wikipedia.org/wiki/Excitatory_synapse#Diseasehttp://en.wikipedia.org/wiki/Excitatory_synapse#Excitotoxicityhttp://en.wikipedia.org/wiki/Excitatory_synapse#Pathophysiologyhttp://en.wikipedia.org/wiki/Excitatory_synapse#Treatmenthttp://en.wikipedia.org/wiki/Excitatory_synapse#Related_neurodegenerative_diseaseshttp://en.wikipedia.org/wiki/Excitatory_synapse#See_alsohttp://en.wikipedia.org/wiki/Excitatory_synapse#Referenceshttp://en.wikipedia.org/w/index.php?title=Excitatory_synapse&action=edit&section=1http://en.wikipedia.org/wiki/Excitatory_synapse#cite_note-Neuroscience.2C_4th_ed.-2http://en.wikipedia.org/wiki/Excitatory_synapse#cite_note-Neuroscience.2C_4th_ed.-2http://en.wikipedia.org/wiki/Caridoid_escape_reactionhttp://en.wikipedia.org/wiki/Caridoid_escape_reactionhttp://en.wikipedia.org/wiki/Excitatory_synapse#cite_note-Neuroscience.2C_4th_ed.-2http://en.wikipedia.org/wiki/Neuropeptideshttp://en.wikipedia.org/wiki/Neuropeptideshttp://en.wikipedia.org/wiki/Excitatory_synapse#cite_note-Neuroscience.2C_4th_ed.-2http://en.wikipedia.org/wiki/Synaptic_clefthttp://en.wikipedia.org/wiki/Synaptic_clefthttp://en.wikipedia.org/w/index.php?title=Excitatory_synapse&action=edit&section=2http://en.wikipedia.org/wiki/File:Synapse.theora.ogvhttp://en.wikipedia.org/wiki/File:Synapse.theora.ogvhttp://en.wikipedia.org/wiki/Excitatory_synapse#Acetylcholinehttp://en.wikipedia.org/wiki/Excitatory_synapse#Glutamatehttp://en.wikipedia.org/wiki/Excitatory_synapse#Catecholamineshttp://en.wikipedia.org/wiki/Excitatory_synapse#Serotoninhttp://en.wikipedia.org/wiki/Excitatory_synapse#Histaminehttp://en.wikipedia.org/wi