EPHAPTIC TRANSMISSION PDF

Some characteristics of ephaptic transmission of action potentials were investigated with squid giant axons. For these studies two isolated axons were placed. Thus, the secondary peaks must represent the orthodromic impulses generated by ephaptic transmission. An average inter-peak interval of ms between the. Ephaptic transmission was implied. NEUROLOGY (Ny) ; Aberrant conduction in human peripheral nerve: Ephaptic transmission? Richard A.

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Ephaptic coupling is a form of communication within the nervous system and is distinct from direct communication systems like electrical synapses and chemical ephaptuc. It may refer to the coupling of adjacent touching nerve fibers caused by the exchange of ions between the cells, or it may refer to coupling of nerve fibers as a result of local electric fields.

Myelination is thought to inhibit ephaptic interactions. The idea that the electrical activity generated by nervous tissue may influence the activity of surrounding nervous tissue is one that dates back to the late 19th century. Early experiments, like those by du Bois-Reymond, [3] demonstrated that the firing of a primary nerve may induce the transmiswion of an adjacent secondary nerve termed “secondary excitation”.

This effect was not quantitatively explored, however, until experiments by Katz and Schmitt [4] inwhen the two explored the electric interaction of two adjacent limb nerves of the crab Carcinus maenas.

Their work demonstrated that the progression of the action potential in the active axon caused excitability changes in the inactive axon. These changes were attributed to the local currents that form the action potential.

Ephaptic transmission in squid giant axons.

For example, the currents that caused the depolarization excitation of the active nerve caused a corresponding hyperpolarization depression of the adjacent resting fiber. Similarly, the currents that caused repolarization of the active nerve caused slight depolarization in the resting fiber.

Katz and Schmitt also observed that stimulation of both nerves could cause interference effects. Simultaneous action potential firing caused interference and resulted in decreased conduction velocitywhile slightly offset stimulation resulted in synchronization of the two impulses. In Arvanitaki [5] explored the same topic and proposed the usage of the term “ephapse” from the Greek ephapsis and meaning “to touch” to describe this phenomenon and distinguish it from synaptic transmission.

Over time the term ephaptic coupling has come to be used not only in cases of electric interaction between adjacent elements, but also more generally to describe the effects induced by any field changes along the cell membrane. The early work performed by Katz and Schmitt demonstrated that ephaptic coupling between the two adjacent nerves was insufficient to stimulate an action potential in the resting nerve. This was accomplished in one study in two experimental conditions: While transmissiln manipulations do not reflect normal conditions, they do highlight the mechanisms behind ephaptic excitation.

Ephaptic coupling has also been found to play an transmissoon role in inhibition of neighboring neurons. Depending on the location and identity of the neurons, various mechanisms have been found to underlie ephaptic inhibition. In one study, newly excited neighboring neurons interfered with already sustained currents, thus lowering the extracellular potential and depolarizing the neuron in relation to its surrounding environment, effectively inhibiting the action potential’s propagation.

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Studies of ephaptic coupling have also focused on its role in the synchronization and timing of action potentials in neurons. In the simpler case of adjacent fibers that experience simultaneous stimulation the impulse is slowed because both fibers are limited to exchange ions solely with the interstitial fluid increasing the resistance of the nerve.

More recent research, however, tdansmission focused on the more general case of electric fields that affect a variety of neurons. It has been observed that local field potentials in cortical neurons can serve to synchronize neuronal activity.

Ephaptic transmission in squid giant axons.

This coupling may effectively synchronize neurons into periods of enhanced excitability or depression and allow for specific patterns of action potential timing often referred to as spike timing.

This ephapticc has been demonstrated and modeled in a variety of cases. A hypothesis or explanation behind the mechanism is “one-way”, “master-slave”, or “unidirectional synchronization” effect as mathematical and fundamental property of non-linear dynamic systems oscillators like neurons to synchronize under certain criteria.

Such phenomenon was proposed and predicted to be possible between two HR neurons, since in simulations and modeling work by Hrg. Hence the phenomenon is of not only fundamental interest but also applied one from treating epilepsy to novel learning systems.

Ephaptic Medical Definition | Merriam-Webster Medical Dictionary

Synchronization of neurons is in principle unwanted behavior, as brain would have zero information or be simply a bulb if all neurons would synchronize.

Hence it is a hypothesis that neurobiology and evolution of brain coped with ways of preventing such synchronous behavior on large scale, tgansmission it rather in other special rtansmission. The electrical conduction system of the heart has been robustly established. However, newer research has been challenging some of the previously accepted models.

The role of ephaptic coupling in cardiac cells is becoming more apparent. There are also a number of mathematical models that more recently incorporate ephaptic coupling into predictions about electrical conductance in the heart. Epileptic seizures occur when there is synchrony of electrical waves in the brain. Knowing the role that ephaptic coupling plays in ephaptc synchrony in electrical signals, it makes sense to look for ephaptic mechanisms in this type of pathology.

One study suggested that cortical cells represent an ideal place to observe ephaptic coupling due to the tight packing of axons, which allows for interactions between their electrical fields. They tested the effects of changing extracellular space which affects local electrical fields and found that one can block epileptic synchronization independent of chemical synapse manipulation simply by increasing the space between cells.

Neurons in the olfactory system are unmyelinated and densely packed and thus the often small effects of ephaptic coupling are more easily seen. A number of studies have shown how inhibition among neurons in the olfactory system work to fine tune integration of signals in response to odor. This inhibition has been shown to occur from changes in electrical potentials alone.

The inhibition due to ephaptic coupling would help account for the integration of signals that gives rise to more nuanced perception of smells. Due to the very small electrical fields produced by neurons, mathematical models are often used in order to test a number of manipulations. Cable theory is one of transmssion most important mathematical equations in neuroscience.

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ephaptic transmission

However, many authors have worked to create more refined models in order to more accurately represent the environments of the nervous system. For example, many authors have proposed models for cardiac tissue that includes additional variables that account for the unique structure and geometry of cardiac cells [14] varying scales of size, [19] or three-dimensional electrodiffusion.

Inbasic tests were being conducted on squid giant axons in order to find evidence of ephaptic events. It was shown that an action potential of one axon could be propagated to a neighboring axon.

The level of transmission varied, from subthreshold changes to initiation of an action potential in a neighboring cell, ephqptic in all cases, it was apparent that there are implications of ephaptic coupling that are of physiological importance. One study tested the effects of ephaptic coupling by using both neurotransmitter anatagonists to block chemical synapses and gap junction blockers to block electrical synapses.

It was found that rhythmic electrical discharge associated with fetal neurons in the rat spinal cord and medulla was still sustained. This suggests that connections between the neurons still exist and work to spread signals even without traditional synapses.

These findings support a model in which ephaptic coupling works alongside canonical synapses to propagate signals across transmissiin networks. One of the few known cases of a functional system in which ephaptic coupling is responsible for an observable physiological event is in the Purkinje cells of the transmssion cerebellum. The firing of these basket cells, which occurs more rapidly than in the Purkinje cells, draws current across the Purkinje cell and generates a passive hyperpolarizing potential which inhibits the activity of the Purkinje cell.

Although the exact functional role of this inhibition is still unclear, it may well have a synchronizing effect in the Purkinje cells as the ephaptic effect will limit the firing time. A similar ephaptic effect has been studied in the Mauthner cells of teleosts. While the idea of non-synaptic interactions between neurons has existed since the 19th century, there has historically been a lot of skepticism in the field of neuroscience. Many people believed that the micro electrical fields produced by the neurons themselves were so small that they were negligible.

Ephaptif it is a true lack of evidence or simply obstinance in the face of change, many in transmisssion field are still not entirely convinced there is unambiguous evidence of ephaptic coupling. From Tranmission, the free encyclopedia. Understanding the brain languageIOS Press, doi: Retrieved from ” https: Neurophysiology Cellular neuroscience Signal transduction.

Views Read Edit View history. This page was last edited ephxptic 11 Novemberat By using this site, you agree to the Terms of Use and Privacy Policy.

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