Q:

Which type of synapse dominates the nervous system?

A:

Quick Answer

Chemical synapses are the prevailing type of synapse in the nervous systems of complex organisms. These synapses are characterized by their substantially larger pre- and postsynaptic spacing, called clefts, as compared to electrical synapses.

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Full Answer

Chemical synapses possess a special type of membrane-bound organelle called a synaptic vesicle in the presynaptic terminal. These organelles are spherical and filled with neurotransmitters, which are chemical signaling agents that act as messengers between communicating neurons. These neurotransmitters are secreted by presynaptic neurons and are the reason for naming chemical synapses by that name. Examples of neurotransmitters include acetylcholine, glutamate, aspartate and nitric oxide.

Different neurotransmitters are used by the chemical synapses in specific parts of the nervous system. Acetylcholine serves as a transmitter in the peripheral neuromuscular synapses, whereas glutamate relays signals between the neurons of the human brain.

The relaying of signals through chemical synapses begins when an action potential floods the presynaptic neuron. This causes the neuron to open voltage-gated calcium channels. The steep concentration gradient resulting in the presynaptic membrane causes calcium ions to fill the presynaptic terminal. This causes the synaptic vesicles to fuse with plasma membranes, allowing the neurotransmitters to fill the synaptic cleft and relay the signal. The neurotransmitters are then cleared from the synapse through enzymatic degradation or reuptake.

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