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Synapse

Synapse

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In the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

, a synapse is a structure that permits a neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

 to pass an electrical or chemical signal to another cell (neural or otherwise). The word "synapse" comes from "synaptein", which Sir Charles Scott Sherrington
Charles Scott Sherrington
Sir Charles Scott Sherrington, OM, GBE, PRS was an English neurophysiologist, histologist, bacteriologist, and a pathologist, Nobel laureate and president of the Royal Society in the early 1920s...

 and colleagues coined from the Greek "syn-" ("together") and "haptein" ("to clasp").

Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so. At a synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

, but some presynaptic sites are located on a dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...

 or soma
Soma (biology)
The soma , or perikaryon , or cyton, is the bulbous end of a neuron, containing the cell nucleus. The word "soma" comes from the Greek σῶμα, meaning "body"; the soma of a neuron is often called the "cell body"...

.

There are two fundamentally different types of synapses:
  • In a chemical synapse
    Chemical synapse
    Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...

    , the presynaptic neuron releases a chemical called a neurotransmitter
    Neurotransmitter
    Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

     that binds to receptors
    Neurotransmitter receptor
    A Neurotransmitter receptor is a membrane receptor protein that is activated by a Neurotransmitter. A membrane protein interacts with the lipid bilayer that encloses the cell and a membrane receptor protein interacts with a chemical in the cells external environment, which binds to the cell...

     located in the postsynaptic cell, usually embedded in the plasma membrane. Binding of the neurotransmitter to a receptor can affect the postsynaptic cell in a wide variety of ways.

  • In an electrical synapse
    Electrical synapse
    An electrical synapse is a mechanical and electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. At gap junctions, such cells approach within about 3.5 nm of each other, a much shorter...

    , the presynaptic and postsynaptic cell membranes are connected by channels that are capable of passing electrical current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell.


Synaptic communication is distinct from ephaptic coupling
Ephaptic coupling
Ephaptic coupling is indirect communication within the nervous system through extracellular electric fields, as opposed to direct communication via electrical synapses or chemical synapses. Ephaptic communication has been observed in myelinated nerve fibers....

, in which communication between neurons occurs via indirect electric fields.

See also

  • Chemical synapse
    Chemical synapse
    Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...

  • Electrical synapse
    Electrical synapse
    An electrical synapse is a mechanical and electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. At gap junctions, such cells approach within about 3.5 nm of each other, a much shorter...

  • Postsynaptic density
    Postsynaptic density
    The postsynaptic density is a protein dense specialization attached to the postsynaptic membrane. PSDs were originally identified by electron microscopy as an electron-dense region at the membrane of a postsynaptic neuron...

  • Active zone
    Active zone
    The active zone is a term first used by Couteaux and Pecot-Dechavassinein in 1970 and is defined in the neuron as the site of neurotransmitter release. Neurons contain structures called synapses that allow for the communication from one neuron to another...

  • Neuron
    Neuron
    A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

  • Neurotransmitter
    Neurotransmitter
    Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

  • Neurotransmitter vesicle
  • Immunological synapse
    Immunological synapse
    In immunology, an immunological synapse is the interface between an antigen-presenting cell and a lymphocyte. It was first discovered by Abraham Kupfer at the National Jewish Medical and Research Center in Denver and the term was coined by Michael Dustin at NYU who studied it in further detail...