Electrical Synapses: What 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 gaps that allow electrical current to pass
Although this type of synapses are more typical of invertebrate and lower vertebrate animals, they have also been observed in some areas of the nervous system of mammals, including humans.
In recent years, electrical synapses have lost prominence in favor of chemical synapses, which are more numerous and complex. In this article we will see what these electrical synapses are like and what characterizes them.
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 routes: the chemical synapse, when the transmission of information occurs by releasing substances or neurotransmitters, and the electrical synapse.
At the electrical synapse, the membranes of pre- and postsynaptic neurons are joined by a gap junction. through which electric current flows from one cell to another and directly
These gap junction channels have low resistance (or high conductance), that is, the passage of electrical current, whether of positively or negatively charged ions, flows from the presynaptic neuron to the postsynaptic neuron, generating either a depolarization, or hyperpolarization.
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
At an electrical synapse, a hyperpolarization occurs when the membrane potential becomes more negative at a particular point on the neuronal membrane, while depolarization occurs when the membrane potential becomes less negative (or more positive).
Both hyperpolarization and depolarization occur when membrane ion channels (proteins that allow specific ions to pass through the cell membrane) open or close, altering the ability of certain types of ions to enter or leave. of the cell.
Differences from chemical synapses
From a functional point of view, Communication between neurons through electrical synapses differs substantially from that which occurs in chemical synapses The main difference is the speed: in the latter, a synaptic delay occurs from the time the action potential reaches the presynaptic terminal until the neurotransmitter is released, while in electrical synapses the delay is practically 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 control points, which ultimately lead to the release and binding of the neurotransmitter with the receptor. All of 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 They are the most common in less complex vertebrate animals and in some areas of the mammalian brain They are faster than chemical synapses but less plastic. All in all, this type of synapse has several very notable advantages:
The electrical synapse has a bidirectional transmission of action potentials Chemistry, however, can only communicate in a one-way manner.
Coordination capacity
In electrical synapses, a synchronization of neuronal activity is generated, which allows nerve cells to coordinate with each other
Speed
Regarding the speed of communication, it is faster in electrical synapses, because the action potentials They travel through the ion channel without having to release any chemicals
Disadvantages
Electrical synapses also have disadvantages compared to chemical synapses. Mainly, 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.
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 depending on the potential difference on both sides of the membranes that form the junction.
In some unions, in fact, This sensitivity to the voltage of the channels allows the depolarizing currents to be conducted in a single direction (what is known as rectifying electrical synapses).
It also happens that most communication channels close in response to a decrease in intracellular pH or due to an increase in cytoplasmic calcium (many of the cell’s metabolic processes occur in the cytoplasm).
It has been suggested that these properties have a protective role by ensuring the uncoupling of injured cells from other cells, since in the former there are significant increases in calcium and cytoplasmic protons that could affect adjacent cells if they crossed the communicating channels.
Numerous investigations have been able to verify that neurons are not connected anarchically with each other, but that the relationships between different nervous centers They follow guidelines that transcend a specific animal species, being characteristic of the animal group
This connectivity between different nervous centers originates during embryonic development and is perfected as it grows and develops. The basic wiring in the different vertebrate animals shows a general similarity, 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 it encounters in its path and these serve as a reference to know how to position and situate itself within the neuronal network.
In neuronal connectivity studies it has also been shown that there is usually a predictable correspondence between the position of neurons in the center of origin and that of their axons in the destination center, making it possible to establish precise topographic maps of the connection between both areas.
