Synapse | Definition, Types & Functions

By | November 18, 2019


Synapse Definition

What is a Synapse: It is a small gap at the end of neurons in the central nervous system. The synapse permits a signal to pass from one neuron to the next neuron. The synapse is a region where two nerve cells connect with each other and exchange their signals. They are the complex organization of multiple inputs, which results in various distinct neurotransmitters released from both neurons and glia.

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How big is a synapse?

Synapses are tiny—you cannot see them with the eye. Once measured by utilizing sophisticated tools, scientists will see that the tiny gaps between cells are just about 20-40 nanometers wide. If you think that the thickness of one sheet of paper is about 100,000 nanometers wide, you’ll be able to start understanding just how tiny these useful contact points between neurons are. Over 3,000 synapses would slot in that space alone!

Types of Synapses:

The human nervous system has various different neurotransmitters and neuroreceptors. According to this, there are five types of synapses.

  • Excitatory Ion Channel Synapses:

These synapses consist of neuroreceptors which are sodium channels. Positive ions flow when these channels open.

  • Inhibitory Ion Channel Synapses:

These synapses consist of neuroreceptors which are chloride channels. Negative ions flow when these channels open.

  • Non-Channel Synapses:

These synapses consist of neuroreceptors which are not channels at all, but instead of these are membrane-bound enzymes.

  • Neuromuscular Junction:

These synapses lie between motor neurons and muscle cells. They use neurotransmitter acetylcholine, and always excitatory.

  • Electrical Synapses:

The two membrane cells actually touch and share proteins together in these synapses. This permits the action potential to pass from one membrane to the next one directly.

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How many Synapses are in the human brain?

The short answer is that neuroscientists aren’t specifically certain about this. It’s terribly arduous to measure in living individuals. However current post-mortem studies, in which scientists examine the brains of deceased people, recommend that the typical male human brain contains approximately 86 billion neurons. If every nerve cell is home to hundreds or maybe thousands of synapses, the estimated range of those communication points should be within the trillions. Current estimates are listed somewhere around zero.15 quadrillion synapses—or 150,000,000,000,000 synapses.

What is the Synaptic Transmission?

Generally speaking, it’s simply difficult to explain neurotransmission. However, it specifies that the communication occurring between brain cells is going on at the synapse as opposed to another communication point. One nerve cell usually observed as the presynaptic cell, it can release neurotransmitters or different neurochemicals from special pouches or clusters near the plasma membrane known as Synaptic vesicles into space between cells.

Those molecules will then be taken up by membrane receptors on the post-synaptic, or neighboring, cell. Once this message is passed between the two cells at the junction, it has the ability to alter the behavior of each cell. Chemicals from the pre-synaptic nerve cell might excite the post-synaptic cell, telling it to release its own neurochemicals. It should tell the post-synaptic cell to slow down signaling or stop it altogether.

Or it should simply tell it to alter the message in a small amount. However, synapses provide the chance of bi-directional communication. As such, post-synaptic cells will send back their own messages to pre-synaptic cells—telling them to alter how much or how typically a neurotransmitter is discharged.


Diffusion of Neurotransmitters cross the Synaptic Cleft:

The molecules of the neurotransmitter diffuse across the synaptic cleft where molecules can bind with the sites of receptors on the postsynaptic ending to influence the electrical response in the postsynaptic neuron.