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What Are Neuron Synapses?

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  • Written By: Kathy Dowling
  • Edited By: A. Joseph
  • Last Modified Date: 27 November 2016
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Neuron synapses can be either electrical or chemical and are the structures that allow neurons in the body to communicate with each other and, essentially, to other areas of the body. Signaling between presynaptic and postsynaptic neurons takes place via neuron synapses, and communication between both occurs as a result of an action potential. Communication is able to take place because of the connection between terminal buttons of one neuron to either another neuron or to a membrane of a nerve cell, such as a gland cell or muscle cell.

An action potential occurs when there is an irregular distribution of positively and negatively charged ions within the axon. Certain ions can enter and exit the axon via ion channels. It is when a number of ion channels nearest the cell body, or soma, of a neuron are opened that an action potential is caused.

The opening of such channels allows positively charged sodium ions to enter the axon, reversing the potential at that position. This causes neighboring channels to open, further creating a reversal in membrane potential at that point. This short-lived electrochemical occurrence is carried down the axon of a neuron to its terminal buttons and is transmitted via neuron synapses.

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The neuron sending a message is called a presynaptic neuron. When the action potential reaches the terminal buttons of the presynaptic neuron, a transmitter substance is released into the synaptic cleft, a gap that is filled with fluid. The postsynaptic neuron, or the neuron that receives the message, is able to do so because of special protein molecules that are located on its membrane. These proteins respond to the transmitter substance that is released into the synaptic cleft from the presynaptic neuron. The signaling between both the presynaptic and postsynaptic neuron can take place only via neuron synapses, and although there are both electrically and chemically charged synapses, there are significantly more chemical ones.

Neuron synapses are either excitatory or inhibitory. The term "excitatory synapses" refers to when the terminal buttons of a neuron discharge substances into the synaptic cleft that excite the postsynaptic neuron. As a result of this, the axon of the postsynaptic neuron is more likely to fire, sending electrochemical signals to different neurons or nerve cells. The more active the excitatory synapse, the quicker the axon will fire.

Inhibitory synapses have a reverse effect. They make the axons of postsynaptic synapses unlikely to fire. The more active the inhibitory synapse, the slower it will fire, if it fires at all.

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