Electrical synapses: how they are and how they work in the nervous system

The main characteristic of our nervous system is its ability to transmit information from one cell to another. This intercellular communication occurs in several ways, and one of them is through electrical synapses, small slits that allow the passage of electrical current.

Although this type of synapse is more typical of invertebrate animals and lower vertebrates, it has also been observed in some areas of the mammalian nervous system, including humans.

In recent years, electrical synapses have lost prominence in favor of more numerous and complex chemical synapses. In this article we will see what these electrical synapses are like and what characterizes them.

• Related article: "What is the synaptic gap and how does it work?"

What are electrical synapses?

The transfer of information between neurons occurs at the level of a specialized junction known as a synapse. In this synaptic space, neurons communicate and use, mainly, two pathways: the synapse chemistry, when the transmission of information occurs by releasing substances or neurotransmitters, and the electrical.

In electrical synapses, the membranes of pre- and postsynaptic neurons are joined by a gap junction, or gap junction. through which electrical current flows from one cell to another and directly.

These gap junction channels have a low resistance (or a high conductance), that is, the passage of electric current, either ions positively or negatively charged, it flows from the presynaptic to the postsynaptic neuron, generating either depolarization or a hyperpolarization.

hyperpolarization and depolarization

At rest, a neuron has a resting potential (potential across the membrane) of -60 to -70 millivolts. This implies that the inside of the cell is negatively charged relative to the outside.

In an electrical synapse, a hyperpolarization occurs when the membrane potential becomes more negative at a particular point of the neuronal membrane, while depolarization occurs when the membrane potential becomes less negative (or more positive).

Both the hyperpolarization such as depolarization occur when ion channels (proteins that allow the passage of specific ions through the cell membrane) of the membrane open or close, which alters the ability of certain types of ions to enter or leave the cell. cell.

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Differences with chemical synapses

From a functional point of view, communication between neurons across electrical synapses differs substantially from that that occurs at chemical synapses. The main difference is speed: in the latter, there is a synaptic delay from when the action potential reaches the presynaptic terminal until the neurotransmitter is released, whereas at electrical synapses the delay is virtually non-existent.

This intercellular communication at such a high speed allows the simultaneous functional coupling (a synchronization) of networks of neurons that are linked by electrical synapses.

Another difference between electrical and chemical synapses lies in their regulation.. The latter must follow a complex multi-step process, subject to numerous checkpoints, which ultimately lead to the release and binding of the neurotransmitter to the receptor. All this contrasts with the simplicity of electrical synapses, where intercellular channels allow the bidirectional flow of ions and small molecules in almost any situation.

Advantages of electrical synapses vs chemical synapses

electrical synapses are the most common in less complex vertebrate animals and in some areas of the brain of mammals. They are faster than chemical synapses but less plastic. However, this type of synapse has several very notable advantages:

Bidirectionality

electrical synapse has a bidirectional transmission of action potentials. Chemistry, however, can only communicate one way.

coordination capacity

Synchronization of neuronal activity is generated in electrical synapses, what makes nerve cells can coordinate with each other.

Speed

Regarding the speed of communication, it is faster in electrical synapses, due to the fact that action potentials travel through the ion channel without having to release any chemicals.

Disadvantages

Electrical synapses also have disadvantages over chemical synapses. Mainly, that they cannot convert an excitatory signal from one neuron into an inhibitory signal in another. That is, they lack the flexibility, versatility, and ability to modulate signals that their chemical counterparts do possess.

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Properties of this type of synapse

Most of the intercellular channels that form electrical synapses are voltage dependent; that is, its conductance (or, conversely, its resistance to the passage of electric current) varies as a function of the potential difference on both sides of the membranes that form the junction.

In some unions, in fact, this channel voltage sensitivity allows depolarizing currents to be conducted in only one direction (what is known as rectifying electrical synapses).

It also happens that most of the communication channels are closed in response to the decrease in intracellular pH or due to an elevation of cytoplasmic calcium (in the cytoplasm many of the metabolic processes of the cell).

It has been suggested that these properties have a protective role by procuring the uncoupling of injured cells by other cells, since in the First, there are significant increases in calcium and cytoplasmic protons that could affect adjacent cells if they crossed the channels. communicators.

neural connectivity

Numerous investigations have been able to verify that neurons are not anarchically connected with each other, but that the relationships between different nerve centers follow guidelines that transcend a specific animal species, being characteristic of the animal group.

This connectivity between different nerve centers originates during embryonic development and is perfected as it grows and develops. The basic wiring in the various vertebrate animals shows a general resemblance, a reflection of gene expression patterns inherited from common ancestors.

During the differentiation of a neuron, its axon grows guided by the chemical characteristics of the structures that form. it finds in its path and these serve as a reference to know how to position itself and situate itself within the neural network.

Studies of neuronal connectivity have also shown that there is usually a predictable correspondence between the position of neurons in the center of origin and that of its axons in the center of destination, being able to establish precise topographic maps of the connection between both zones.

Bibliographic references:

• Waxman, S. (2012). Clinical neuroanatomy. Padua: Piccin.