Wiktor Wise
Electrical synapses are a type of neurophysiological connection that allows for the rapid transmission of electrical signals between neurons. They are formed by gap junctions, which are composed of proteins called connexins that create a direct channel for ionic current to flow between cells. These electrical synapses are found in various tissues, including the nervous system, with examples such as the crayfish nervous system, the mammalian hypothalamus, and the human brain. They are also present in the visceral smooth muscles and cardiac muscle, enabling direct signal transmission between neighbouring muscle cells. Electrical synapses facilitate synchrony and enhance sensitivity to stimuli, showcasing their diverse functions in different tissues.
| Characteristics | Values |
|---|---|
| Tissue types | Nervous systems, including the human brain, cardiac muscle, visceral smooth muscles, and other tissues such as internal organs, blood vessels, intestines, and glands (eyes, sweat, saliva, tears, endocrine) |
| Function | Synchronization of electrical activity among populations of neurons, enhanced sensitivity to stimuli or neural input, coordination of intracellular signaling and metabolism of coupled neurons |
| Structure | Two membranes located very close together (a few nanometers apart) with channels formed by proteins called connexins, allowing the passage of ions and small molecules |
| Transmission | Bidirectional, virtually instantaneous transmission of electrical signals without the use of neurotransmitters |
| Types of Synapses | Electrical and chemical (majority in mammals) |
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What You'll Learn
- Electrical synapses are found in the human brain and all nervous systems
- They are formed by proteins called connexins
- They allow the bidirectional flow of current between neurons
- They are associated with synchrony and can promote it at many anatomical and frequency ranges across the brain
- They are found in other types of tissue, including visceral smooth muscles and cardiac muscle
Electrical synapses are found in the human brain and all nervous systems
Electrical synapses are a type of junction between neurons that allow the bidirectional flow of electrical current between neurons. They are formed by proteins called connexins, which provide a low-resistance conduit between cells where ions and other small molecules can pass directly from one neuron to another. Electrical synapses are a minority, but they are found in all nervous systems, including the human brain.
In the human brain, electrical synapses are found in the cortex, hippocampus, thalamus, retina, cerebellum, and inferior olive. They are also found in other types of tissue, such as visceral smooth muscles and cardiac muscle. In the brain, electrical synapses are involved in synchronizing the electrical activity of populations of neurons. They are particularly important for certain functions that require a quick response, such as the crayfish nervous system, which allows the crayfish to escape from its predators.
The structure of an electrical synapse consists of two membranes located very close together, with a distance of just a few nanometers. These membranes are joined by an intercellular specialization called a gap junction, which contains precisely aligned, paired channels in the membrane of the pre- and postsynaptic neurons. The gap junction channel is much larger than the pores of voltage-gated ion channels, allowing a variety of substances to diffuse between the cytoplasm of the pre- and postsynaptic neurons.
The transmission of electrical signals through gap junctions is very rapid and can occur in both directions. This is in contrast to chemical synapses, which are the most common type of synapse in the mammalian central nervous system. Chemical synapses use neurotransmitters to relay signals and exhibit synaptic delays due to the time it takes for the neurotransmitter to diffuse across the cleft between the pre- and postsynaptic membranes.
Overall, electrical synapses play an important role in the nervous system by allowing for rapid communication and synchronization between neurons. They are found in a variety of tissues, including the human brain, and contribute to essential functions such as the crayfish escape response.
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They are formed by proteins called connexins
Electrical synapses are formed by proteins called connexins. Connexins are transmembrane proteins coded for by about 20 different genes (mouse, human). Connexin proteins conform to a similar structural organization, composed of four transmembrane, two extracellular, and three cytosolic subdomains. The carboxy-terminal cytosolic tail is the most variable portion of the connexin molecule in terms of both length and composition. The remaining N-domain is capable of self-assembly and hexamer formation and is conserved between members of the connexin family.
Connexins form intercellular communicating channels (aqueous pores) termed gap junctions (GJ). Gap junctions are composed of two hemichannels, or connexons, which consist of homo- or heterohexameric arrays of connexins. Each connexon is made up of six connexin subunits, each of which consists of four transmembrane segments. The connexon in one plasma membrane docks end-to-end with a connexon in the membrane of a closely opposed cell to form the complete intercellular gap junction channel.
The gap junction channel allows for the bidirectional flow of ions and small molecules of less than 1000 Da. This facilitates electrical and chemical coupling between cells, allowing passage of small molecules and electrical impulses directly between cells.
Connexins have been found to be expressed in a wide range of tissues and organs, including the esophagus, liver, bladder, and breast. They play important roles in maintaining homeostasis in the liver and proper function of the kidneys. Connexins also have non-channel-dependent functions relating to the cytoskeleton and cell migration.
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They allow the bidirectional flow of current between neurons
Electrical synapses are formed by gap junctions, which are composed of connexin proteins. These gap junctions are bidirectional, allowing the flow of current and small molecules in both directions between neurons. This is in contrast to chemical synapses, which are predominantly unidirectional and rely on neurotransmitters to transmit signals.
The gap junctional pores in electrical synapses are large enough for the passage of ions and molecules with molecular weights of several hundred daltons. This includes molecules such as ATP and second messengers, which are important for intracellular signalling and metabolism. The transmission of current through these gap junctions is extremely rapid, allowing for almost instantaneous communication between neurons.
The bidirectional nature of electrical synapses has important implications for the synchronization of neural activity. By allowing the flow of current in both directions, electrical synapses enable the reduction of voltage differences between coupled neurons, promoting synchrony. This is particularly crucial in certain physiological processes, such as the synchronized beating of the heart and the coordinated activity of neurons in specialized regions of the adult brain.
Furthermore, the bidirectional flow of current in electrical synapses contributes to the rapid transmission of signals. In the crayfish nervous system, for example, electrical synapses facilitate quick escape responses to predators. The bidirectional transmission allows for a minimal delay in the transmission of electrical signals, ensuring a swift motor response to threatening stimuli.
While electrical synapses are less common than chemical synapses in the brain, they play a significant role in synchronizing and enhancing neural activity. The bidirectional flow of current through gap junctions enables the efficient transmission of signals and the coordination of neuronal functions.
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They are associated with synchrony and can promote it at many anatomical and frequency ranges across the brain
Electrical synapses are formed by gap junctions between neurons, allowing the bidirectional flow of ionic current between neurons. They are found in all nervous systems, including the human brain, and are associated with synchrony.
The continuous conductance provided by gap junctions facilitates the reduction of voltage differences between coupled neurons, promoting synchrony at many anatomical and frequency ranges across the brain. For example, electrical synapses ensure that certain hormone-secreting neurons within the mammalian hypothalamus fire action potentials at about the same time, facilitating a burst of hormone secretion. They also synchronize electrical activity among populations of neurons in crayfish, allowing them to escape from predators with minimal delay between the presence of a threatening stimulus and a motor response.
Additionally, electrical synapses between inhibitory interneurons in the murine cortex have been observed to spike together when depolarized. In the feline inferior olive, electrical synapses have been associated with synchrony, and in the retina, they enhance responses to low-contrast and moving stimuli.
The computational functions of electrical synapses are more complex than just speed and synchrony. They can also play a role in coordinating and synchronizing the activity of neural networks, as well as in excitation and inhibition, rhythm augmentation, phase-shifting, coincidence detection, signal enhancement, adaptation, and interaction with nonlinear membrane and transmitter-release mechanisms.
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They are found in other types of tissue, including visceral smooth muscles and cardiac muscle
Smooth muscle is sometimes referred to as visceral muscle. It is found in the walls of hollow organs like the heart, stomach, bladder, and blood vessels. Smooth muscle is involuntary and lacks striations. It is structurally distinct from striated muscle, which is used for skeletal movement. Smooth muscle is also significantly smaller than striated muscle.
Cardiac muscle, also known as heart muscle or myocardium, is another type of involuntary, striated muscle. It constitutes the main tissue of the heart wall, forming a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). Cardiac muscle cells, or cardiomyocytes, are contractile cells surrounded by an extracellular matrix produced by supporting fibroblast cells.
Electrical synapses are found in all nervous systems, including the human brain. They are formed by gap junctional pores between neurons, which allow the bidirectional flow of ionic currents. Electrical synapses facilitate the synchronisation of electrical activity among populations of neurons, ensuring that all cells fire action potentials simultaneously.
Visceral smooth muscles and cardiac muscles exhibit electrical synapses. In visceral smooth muscles, the cells of single-unit visceral muscle are chemically coupled to one another by gap junctions. These gap junctions exhibit spontaneous action potentials and consist of structurally independent muscle fibres. In cardiac muscle, specialised cardiomyocytes known as pacemaker cells are responsible for setting the rhythm of heart contractions. These pacemaker cells are weakly contractile and are connected to neighbouring contractile cells via gap junctions.
Therefore, both visceral smooth muscles and cardiac muscles possess gap junctions, which are integral to the formation of electrical synapses.
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Frequently asked questions
Electrical synapses are found in all nervous systems, including the human brain. They are also found in the visceral smooth muscles and cardiac muscle.
Electrical synapses are junctions that allow direct current flow between coupled neurons. They are formed by proteins called connexins, which provide a low-resistance conduit between cells.
Electrical synapses allow ionic current to flow passively through gap junction pores from one neuron to another. This results in the transmission of electrical signals.
Electrical synapses are found in the cortex, hippocampus, thalamus, retina, cerebellum, and inferior olive. They are also present in the crayfish nervous system and the feline inferior olive.
Chemical synapses are the most common type in the mammalian central nervous system. They rely on neurotransmitters to relay signals, whereas electrical synapses transmit signals directly and without the use of neurotransmitters.
