Introduction:

Like many cells, the function of neurons to facilitate the many processes they carry out depends on communication to it’s likening cells. Although neurons contain many organelles, those that are most essential to the transmission of information between cells are the dendrites and the axons along the axonal membrane. Neurons are the building blocks of our brain and consciousness, and therefore require numerous  to regulate tasks such as storing information/memory, controlling movement, and communicating between one another. In the average human brain, there are 100 billion neurons with close to 60-100 trillion synapses. A single neuron averagely transmits information through 7,000 synapses before termination. Neural transmission is the act of transferring information from one nerve cell to another synaptically. 

The most basic definition of a synapse is an intercellular space between neurons that serves as a path for means of communication between neurons. There are many types of synapses, each carrying out different functions with different outcomes. Synapses can be either inhibitory, a transmission of information that can deactivate a neuron; or they can be excitatory, information transmission that excites or activates a neuron. Function of these cells also corresponds to location in the body and what the point of termination is. The most common of these junctions are axodendritic synapses-one that carries information from the end of a dendrite to the tip of an axon on the receiving cell. Synapses that are carried out on an axon and are received by the end of another axon are referred as axoaxonic; similarly, synapses carried out by dendrites and received by another dendrite are dendrodendritic. Through synapses, an electrical  impulse is emitted between the space or junction between two neurons which is followed by a chemical impulse carried out by neurotransmitters. Neurotransmitters act as chemical messengers, and aid in carrying the information from the neuron to the next and so on. Although there are many types of neurotransmitters in our nervous system, the four most common ones are acetylcholine, noradrenaline, dopamine, and serotonin. Each of these neurotransmitters serve different functions in our body that are vital for our health. 

Chemical Synapses: 

Over the years, studies have been carried out to clarify this phenomena preceding arguments on whether synaptic transmission is chemical or electrical; later on settling on both. During a chemical synapse, axons promote action potential to release sodium and potassium ions out of the cellular membrane. The cell membrane becomes polarized-a negatively charged interior and positively charged exterior-and allows for sodium channels to open. The membrane potential of a neuron is 70 millivolts at rest and decreases then increases before returning to normal during a chemical synapse. When sodium ions enter the cell, ion potential decreases from 70 millivolts to 55 millivolts, and sodium ions continue to move diffuse. Once membrane potential reaches 35 millivolts, sodium ion channels close and potassium ion channels open resulting in the potassium concentration in the cell to decrease as well as the membrane potential. This process is called repolarization. Action potential occurs within the synaptic knob (also referred to as presynapse) in regards to the recipient of information in this instance. Presynapse refers to the transmitting side  and postsynapse refers to the receiving side of a neuron during the transmission process. Postsynapse is carried out by the receiving cell’s axons or dendrites to acquire the information given by the cell. Once the information has been received during postsynapse a synaptic vesicle transports the information to a neurotransmitter within the vesicle. The release of neurotransmitters is made possible by the synaptic delay, or the time between the arrival of the action potential. When action potential is discharged, the opening allows for calcium channels to open, which triggers the release of neurotransmitters into the synaptic cleft. This process is constantly repeated, synaptic vesicles immediately starting to synthesize neurotransmitters to carry out this procedure. The process of chemical synapses is carried out by many species for general brain function and bodily movement but another means of this process is electrical synapses, transmission by utilizing voltage.

Electrical Synapses: 

Electrical synapses, or gap junctions, occur when there is a fusion between the presynapse and postsynapse membranes. While this process was previously believed to only occur within vertebrae and other prehistoric organisms, this was later proven to be false after close inspection of mammal cells with the invention of new technology. Unlike chemical synapses, the transmission between neurons occurs through voltage signals. This allows for action potential to pass through the membrane without interference from a neurotransmitter and can generate a defective signal. The gap junction causes the signal to potentially lose direction and can result in a signal that travels to an illintending cell. However, with further study on electrical synapses and how they differ from chemical synapses, scientists came across an unexpected discovery. Electrical synapses allow a greater plasticity among the exchange of information between neurons. This is important because along with this increasing plasticity comes more flexibility to improve the function of the nervous system. Despite this, there is still significance in resistance between gap junction and the postsynaptic cell due to voltage sensitivity between cells making electrical synapses less effective. Because these synapses are so sensitive, conditions that may affect conductivity in the cell change in a matter of seconds and sometimes over the course of days through voltage gating. Whilst these factors do affect the role of electrical synapses in neural transmission, it doesn’t deter from the impact and positive effects they have in our nervous system; from simple muscle movement to driving the operation of the spinal cord.

Denouement:

There are many unique attributes of both methods of synaptic transmission. Chemical synapses utilize ions to facilitate the opening of channels between cells to share information, while electrical synapses release a voltage to exchange information through the membrane of two neurons using the organelles on the outside of a cell. Either method is essential to reaching the same goal of discharging information between cells to provide direction for our central nervous system and the bodily systems they depend on, from the retinas to our eyes, the regions in our brain, and the intricate workings of our spinal cord.

Citations: 

Bennett, Michael V.L. "Seeing is relieving: electrical synapses between visualized neurons." Nature Neuroscience, vol. 3, no. 1, 2000, p. 7+. Gale In Context: Science, link.gale.com/apps/doc/A185568889/SCIC?u=j061901007&sid=SCIC&xid=1fc553e0. Accessed 5 Apr. 2021.

Burt, Alvin M., and Roxanne Jamroz Argie. "Synaptic Transmission." Biology, edited by Melissa Sue Hill, 2nd ed., vol. 4, Macmillan Reference USA, 2016, pp. 146-149. Gale In Context: Science, link.gale.com/apps/doc/CX3629800411/SCIC?u=j061901007&sid=SCIC&xid=87483cec. Accessed 5 Apr. 2021.

Curti, Sebastian, and John O'Brien. "Characteristics and plasticity of electrical synaptic transmission." BMC Cell Biology, vol. 17, no. 11, 2016. Gale In Context: Science, link.gale.com/apps/doc/A453317684/SCIC?u=j061901007&sid=SCIC&xid=0970277e. Accessed 5 Apr. 2021.