Neuronal synapse: what it is and how it works

Recent studies have estimated thathumans have approximately 100,000 million neurons in their brain, that is, 10^11 cell bodies specialized in the transmission of electrical signals only in the brain, equivalent to 14 times the world population.

It is not surprising, therefore, that it is estimated that the brain consumes about 300 kilocalories every 24 hours simply functioning, which is 17% of our daily energy intake, despite representing only 2% of our body weight. Without a doubt, thinking costs energy, effort and continuous dedication over time.

All these data help us to circumscribe the brain from a functional point of view, but how does the information get to this organ and what is the method of transmission of it? Today we come to answer this question thoroughly, because we tell you everything you need to know about neuronal synapses. Don’t miss it.

• We recommend you read: “The 16 types of neurons (functions and characteristics)”

What is neuronal synapse?

The synapse is defined as the point of communication between two neurons or betweena neuron and a target cell, such as a muscle tissue that must perform a movement “commanded” by the brain, or a gland, which must secrete a specific hormone into the bloodstream. For two entities to communicate, there must be a sender and a receiver, right?

Therefore, we know as “presynaptic neuron” the one that sends the impulse, while the cell (whether neuron or part of another tissue) “postsynaptic” is the one that receives the signal. At this point, it is necessary to emphasize that there are two types of synaptic signals. We tell you in broad strokes.

1. Survival synaptic activity

This is developed in the following contexts:

• Communication between two neurons: the stimulus is transported by amino acid-type neurotransmitters, which are the functional units that form proteins.
• Communication between a neuron and a muscle cell: to promote the contraction of a muscle, ester-type neurotransmitters participate.
• Communication between a neuron and a secretory cell: for a gland to secrete a hormonal substance, neuropeptide-type transmitters are required, that is, bonds of 3 or more amino acids acting on the nervous system.

2. Survival synaptic activity

Survival synaptic activity takes place in the following contexts:

• In neuroprocreative activity.
• In the activity of consumption and intake of food.
• In the activity of extreme homeostatic preservation, that is, the regulation of internal balance at metabolic levels.

Thus, we can see that they are two sides of the same coin. The synaptic activity of survival refers to the “microscopic” mechanisms that occur in cellular communication, while survival encompasses those activities that keep us survivors, worth the redundancy, such as the regulation of temperature / body fluids (homeostasis) or food intake.

Types of synapses

While we have laid the foundations for synaptic connections in a cursory way, we have not explored their basic chemical typology. We tell you the two main types of synapses below.

1. Electrical synapse

Perhaps the best known at an informative level. At the electrical synapse, the membranes of the “pre-” and “post-” cells are joined by a gap-like or communicating junction, inserts where two cells are contiguous and, precisely aligned, the light of one is continuous with that of the other. Thanks to these “microbridges”, between both neurons there is a communication channelthrough which ionic currents can flow from one cell to another directly.

Electrical synapses are the most common in less complex vertebrates and can also be seen in some parts of the mammalian brain. This type of cellular communication has 2 important advantages:

• It has a two-way transmission, that is, the channels communicate “back and forth”. This makes it possible to synchronize neurons so that they maintain a coupled rhythm.
• Communication is faster at the electrical synapse than in chemistry. Action potentials pass through channels without the need for neurotransmitters.

2. Chemical synapse

We advance a little in complexity, because in this casethere is a literal physical space that the cells must solve to communicate. In this type of synapse, neurons are separated by a gap of about 20-30 nanometers: the synaptic cleft. To bridge this space, the presynaptic neuron releases an information-carrying agent: the neurotransmitter. For this transmission to be produced successfully, the machinery must have the following elements:

• Presynaptic element: The terminal part of the neuron, the axon, contains synaptic vesicles that store neurotransmitters (10,000 to 50,000 per vesicle).
• The synaptic cleft, this space that usually oscillates between 20 and 50 nm.
• Postsynaptic element: the recipient cell must present receptors for neurotransmitters, which will modify their action potential.

So if this event is more complex and expensive than the electrical synapse, why is it more widespread in evolutionarily complex animals? The answer is simple: plasticity. The direct drive electric potential is an all-or-nothing, on-off switch: it either happens or it doesn’t.

On the other hand, the chemical synapse can be modulated, because the amount of the neurotransmitter released can “rise” or “fall” based on the arrival of a specific potential. Similarly, a post-synaptic cell can alter the number of receptors in its membrane and the ease with which they interact with neurotransmitters. These changes can weaken or strengthen a particular synapse, a range of variation that goes far beyond a simple “on/off.”

How is neuronal synapse produced?

If we look at the human species, it is much more biological interest to describe the chemical synapse, since it is the one that occurs in most of our body when talking about signal transmission. We explain this process quickly and easily.

Although sometimes the release of neurotransmitters can occur spontaneously, in most cases a stimulus is required in the form of an action potential. When a nerve impulse travels through the neuron (the axon, the “tail”), there is a massive influx of calcium ions inside, which cause the synaptic vesicles to attach to the membrane of the axon terminal, thus releasing neurotransmitters to the synaptic cleft.

The neurotransmitter diffuses through the cleft very quicklyand some of it binds with the postsynaptic receptors of the new cell. Within these receivers, there are 2 basic systems:

• The receptors directly activate the ion channels.
• The receptors activate ion channels indirectly through a series of transduction mechanisms and second messengers.

Be that as it may, the arrival of the neurotransmitter to the post-synaptic cell modifies the properties of its membrane, allowing ions to flow in or out of it, which generates the synaptic response itself.