Difference Between Chemical and Electrical Synapse

Key Difference – Chemical vs Electrical Synapse
 

Chemical and electrical synapses are specialized biological structures found in the nervous system; they connect neurons together and transmit signals across the neurons. The key difference between chemical and electrical synapse is their method of transmitting signals; chemical synapse pass signals in the form of chemical molecules called neurotransmitters while electrical synapse transmits signals in the form of electrical signals without the use of molecules. The structure of chemical synapse and electrical synapse is also slightly different from each other due to their mode of action.

CONTENTS
1. Overview and Key Difference
2. What is Synapse
3. What is Chemical Synapse
4. What is Electrical Synapse
5. Side by Side Comparison – Chemical vs Electrical Synapse
6. Summary

What is a Synapse?

A synapse can be defined as a structure mediating the transmission of signals from one neuron to the adjacent neuron. Synapses are found in the nervous system. They can transmit either electrical signals or chemical signals. Synapses can be classified two main types according to this type of the signal: electrical synapse and chemical synapse. At the synapse, the communicating two neurons come closer by their plasma membranes to pass the signal accurately and efficiently. The neuron which sends the signal consists of the presynaptic end while the neuron receiving the signal consists of the postsynaptic end. These ends can be seen in axon and dendrite/soma respectively.

What is Chemical Synapse?

Chemical synapse is a biological structure that can be found among two neurons or among a neuron and a nonneuronal cell and its main function is to communicate with each other via chemical messengers as shown in figure 01. These chemical messengers are known as neurotransmitters. Neurotransmitters are produced and packaged inside the small vesicles known as synaptic vesicles. Synaptic vesicles are filled with neurotransmitters and accumulate near the presynaptic end of the presynaptic neuron. When the action potential changes in the presynaptic neuron membrane, these neurotransmitters are released by exocytosis to a space called synaptic cleft. Once these neurotransmitters enter into the synaptic cleft, they bind with the specific receptors located on the surface of the postsynaptic neuron and give the information. This is the type of chemical signal transmission that occurs at the chemical synapse; thus, these structures are of utmost importance to connect the nervous system without collapse. Signal transmission through chemical synapse occurs in only one direction.

One organism contains a huge number of chemical synapse in its nervous system. An adult may have 1000 to 5000 trillion chemical synapses in the central nervous system. This number can vary with the age.

Figure_1: Chemical Synapse

What is an Electrical Synapse?

An electrical synapse is a structure which facilitates two neurons to communicate with each other through electrical signals without any chemical involvement. In an electrical synapse, presynaptic neuron membrane and postsynaptic neuron membrane come extremely closer to each other and connect by making a channel called gap junction as shown in figure 2. Then the signal which is in the form of ionic current, flows through the gap junction passively, allowing the signal transmission. A gap junction is formed using protein channels called connexons. Connexons are tube-like proteins which make a passage through two neurons.

Figure_2: Connexon and connexin structure

What is the difference between Chemical and Electrical Synapse?

Summary –  Chemical vs Electrical Synapse

There are two main types of synapses called chemical and electrical synapses. Chemical synapse uses chemicals called neurotransmitters to transmit signals along the neurons and facilitates a unidirectional transmission. Electrical synapse uses an ionic current to transmit signals along the neurons and facilitates transmission in both directions. The space between two neurons in the chemical synapse is larger and is known as synaptic cleft. Neurotransmitters are diffused in the synaptic cleft till they find their specific receptors. Two neurons in the electric synapse physically connect with each other through gap junctions; hence, the space is very small.

Reference:
1. Purves, Dale. “Chemical Synapses.” Neuroscience. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 06 Feb. 2017
2. Purves, Dale. “Electrical Synapses.” Neuroscience. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 06 Feb. 2017
3. Nicholls, J. G., and D. Purves. “A comparison of chemical and electrical synaptic transmission between single sensory cells and a motoneurone in the central nervous system of the leech.” The Journal of Physiology. U.S. National Library of Medicine, Sept. 1972. Web. 06 Feb. 2017

Image Courtesy:
1.”1225 Chemical Synapse” By OpenStax –  (CC BY 4.0) via Commons Wikimedia
2. “Connexon and connexin structure” By Mariana Ruiz LadyofHats –  (Public Domain) via Commons Wikimedia

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