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Electrical transmission vs Chemical transmission

Electrical transmission vs Chemical transmission


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"The advantage of electrical transmission, apart from speed, is it can favour synchrony in firing. For example, in the brain stem a nucleus called the inferior olive can generate oscillations due to gap junctions."

Can somebody explain this idea? I do not understand the meaning of oscillations in this context. Do they mean that the neuron can send impulses and receive them at the same rate ? Is that what they're trying to put across ?

Source:Lecture Handouts


Electrical transmission vs Chemical transmission - Biology

Ritika Goyal answered this

Chemical transmission at synapse:

Transmission of impulse across synapse usually occurs through chemical transmission, this means that with the help of chemical molecules the impulse is transferred from one neuron to the other through the synapse. The following steps occurs during chemical transmission:

1) Synthesis of neurotransmitter by presynaptic neuron

2) Neurotransmitters are packed into small vesicles and reach the synaptic terminal.

3) Upon receiving a signal, the neurotransmitters are released into the synaptic cleft. From there they swim across the synapse and reach the receptors present on the post synaptic neuron.

4) Neurotransmitter binds to the receptors and these receptors convert the signals to electrical signals again. The electrical signal is further transported across the neuron.

5) After transmission the neurotransmitter is degraded and synapse is cleared to receive the next signal.

Electrical transmission at nerve fibres:

Electrical transmission of impulse at nerve fibres occurs with the help of action potential. Action potential transfers signal from one point of the nerve fibre to another.

Various voltage gated ion channels regulate the electrical transmission. The steps are as follows:

1) Resting stage: The membranes of nerve fibre are maintained at a resting potential of -70 mV under normal conditions.

2) As a stimulus is received by the dendrites of a nerve cell. The Na + channels in the membrane open. If the signal is enough to reach a threshold value of - 50 to -55 mV, then the process continues.

3) Depolarization: More sodium channels open.The Na + influx drives the interior of the cell membrane up to about +30 mV. The process to this point is called depolarization.

4) After reaching the maximum potential, the Na + channels close and the K + channels open. The membrane begins to repolarize back to resting potential.

5) Hyperpolarization: The membrane potential goes below the resting potential. This is hyperpolarization and its is important for the preparation of the neurons fibres for the next signal.


What is a Chemical Synapse

A chemical synapse refers to the cell junctions through which the nerve impulses are transmitted in one direction by means of neurotransmitters. The two plasma membranes are called pre-synaptic and post-synaptic membranes. The pre-synaptic membrane is in the pre-synaptic cell, and the post-synaptic membrane is in the post-synaptic cell. The synaptic cleft is between the pre-synaptic and post-synaptic membranes. A chemical synapse is shown in figure 1.

Figure 1: Chemical Synapse

The synaptic cleft is filled with interstitial fluid. When an action potential is received to the terminal of the pre-synaptic membrane, the voltage-gated calcium channels of the pre-synaptic membrane are opened. Generally, the concentration of the calcium ions in the synaptic cleft is 10-3 M, and that of the inside of nerve cells is 10-7 M. Therefore, calcium ions move from the synaptic cleft into the pre-synaptic nerve cell through calcium channels. This increases the calcium concentration inside the pre-synaptic nerve cell, allowing the synaptic vesicles to fuse with the pre-synaptic membrane to release neurotransmitters to the synaptic cleft by exocytosis. These neurotransmitters diffuse through the synaptic cleft to bind to the receptors in the post-synaptic membrane. They induce an action potential on the membrane of the post-synaptic neuron.


A comparison of chemical and electrical synaptic transmission between single sensory cells and a motoneurone in the central nervous system of the leech

In leech ganglia, three sensory cells of different modality converge on a motoneurone, where they form chemical and electrical synapses. Each of these synapses behaves in a characteristic manner and the nature of the transmission mechanism has significant functional consequences for the operation of the reflexes. An analysis has been made of the effects of trains of impulses on synaptic transmission through these pathways, using frequencies that correspond to natural firing.1. At the chemical synapse between the nociceptive sensory cell and the motoneurone, two opposing events occur: facilitation and depression. Thus, with trains of impulses, the synaptic potentials first increase in amplitude and then decrease. The two processes could be separated by altering the Mg and Ca content of the bathing fluid. In concentrations of Mg that reduced the amplitude of a single control chemical synaptic potential, pure facilitation occurred during a train. Depression predominated during brief trains in raised concentrations of Ca, although synaptic potentials were initially larger. These results suggest that changes in the amount of transmitter released by each presynaptic action potential can account for the changes observed in chemical synaptic transmission.2. In contrast, electrical transmission between the sensory cell responding to touch and the same motoneurone did not show facilitation or depression. The electrical coupling potential in the motoneurone was relatively constant when the touch cell fired at high or low frequencies in normal Ringer fluid, high Mg, or high Ca fluid.3. Further differences between chemical and electrical synapses were apparent when the preparation was cooled to 4 degrees C. In the cold the latency of chemically evoked synaptic potentials in the motoneurone increased and their amplitude declined drastically with repetitive stimulation, while electrical coupling potentials were unaffected.4. A brief hyperpolarization of the presynaptic cell by injected current produced a marked and prolonged increase in chemically evoked synaptic potentials, but did not influence electrical synaptic transmission.5. The synapses of the sensory cell responding to pressure, which are both chemical and electrical, behaved as expected: the chemical synaptic potentials showed facilitation and depression while electrical transmission remained relatively constant.6. These experiments emphasize the different functional consequences of electrical or chemical synapses in reflex pathways for the transmission of signals that arise as a result of natural sensory stimuli.


Synaptic transmission

Paul Johns BSc BM MSc FRCPath , in Clinical Neuroscience , 2014

Electrical synapses

Electrical synapses are also known as gap junctions and are direct points of contact between the cytoplasm of adjacent neurons (Greek: sunapsis, point of contact). This allows very rapid two-way communication and synchronization of electrical discharges.

A gap junction is composed of around 100 intercellular channels called connexons that are inserted into the plasma membranes of adjacent cells ( Fig. 7.1 ). Each connexon is composed of a hexagonal array of proteins called connexins, surrounding an aqueous channel that is 2 nm wide. The pores in adjacent cell membranes are aligned to form a ‘tunnel’ between the two cells. These can be opened or closed by a conformational change in the constituent proteins, regulated by phosphorylation state.

Gap junctions represent a low-resistance pathway that allows charged particles and small molecules to flow freely in either direction and couples the electrical activity of adjoining cells. Groups of cells linked by gap junctions form an electrical syncytium which can generate large, synchronized discharges. This happens in certain brain stem nuclei that control breathing and may contribute to the generation of abnormally synchronized discharges in some forms of epilepsy ( Ch. 11 ).


Electrical Synapses and Learning–Induced Plasticity in Motor Rhythmogenesis

R. Nargeot , A. Bédécarrats , in Network Functions and Plasticity , 2017

2.1 Electrical Synapses in Rhythmic Motor Pattern Genesis

Electrical synapses are present in many structures of the central nervous system (CNS) that underlie the genesis of behaviors in vertebrates and invertebrates. In vertebrates, for example, they are widespread in the premotor and motor cortices ( Gibson et al., 1999 ), the striatum ( Koos and Tepper, 1999 ), the olivary–cerebellar complex ( Sotelo and Llinas, 1972 De Zeeuw et al., 1998 ), and the spinal cord ( Fulton et al., 1980 Tresch and Kiehn, 2000 ).

The functional implication of electrical synapses in motor rhythmogenesis has been investigated in the spinal cord where rhythmic locomotor movements of the fore- and hind limbs are generated. In specific modulatory conditions, a periodic locomotor activity pattern, so-called fictive locomotion, can be recorded from the ventral roots of isolated spinal cords from the neonatal rat. A periodic activity can still be recorded from these spinal ventral roots in the absence of calcium ions which blocks chemical synapses, or in the presence of tetrodotoxin, a sodium channel blocker that abolishes action potential–dependent chemical synaptic transmission ( Tresch and Kiehn, 2000 ). This persistent rhythmic motor activity, as well as normal fictive locomotion, was found to be suppressed by carbenoxolone, a pharmacological blocker of gap junctions. Thus, electrical synapses appear to be essential, although not necessarily exclusively responsible, for the periodic motor pattern genesis in the spinal cord of newborn animals ( Tresch and Kiehn, 2000 Li and Rekling, 2017 ( Chapter 11 ). Although the neuronal origin of this oscillatory activity has yet to be identified, electrical synapses have been found between different spinal neurons including excitatory interneurons and motoneurons that contribute to the motor pattern genesis ( Fulton et al., 1980 Rash et al., 1996 Kiehn and Tresch, 2002 Hinckley and Ziskind-Conhaim, 2006 Song et al., 2016 ).

Theoretical studies have indicated that electrical synapses among a population of nonoscillating neurons are sufficient to produce a regular oscillatory activity ( Sherman and Rinzel, 1992 Smolen et al., 1993 Traub et al., 2017 ( Chapter 13 )). However, in biological networks, these synapses often operate in conjunction with oscillatory intrinsic membrane properties of the electrically coupled neurons ( Tresch and Kiehn, 2000 Rekling et al., 2000 Blatow et al., 2003 Leznik and Llinas, 2005 ). Thus, in addition to their participation in the actual genesis of oscillatory activity, electrical synapses can regulate the synchronization, frequency, and variability of an oscillatory activity produced by endogenous pacemaker or bursting neurons.

Such regulatory roles have been investigated in the pyloric network of the crustacean stomatogastric nervous system ( Nadim et al., 2017 ( Chapter 4 ) where this network generates the cyclic motor output pattern that drives alternate constriction/dilatation movements of the foregut pyloric chamber. This highly regular repetitive motor activity is driven by a kernel of electrically coupled oscillatory cells composed of the AB interneuron and two PD motoneurons ( Selverston and Miller, 1980 ). In experimental conditions of in situ synaptic isolation from their partners in the pyloric network, each of these neurons can individually generate spontaneous oscillatory bursting activity ( Miller and Selverston, 1982 Bal et al., 1988 ). This activity differs according to the cell type as a result of their differing intrinsic membrane properties. The AB neuron is the only pacemaker cell that spontaneously generates a regular oscillation at a frequency similar to that of the normal pyloric motor rhythm. In contrast, the two PD neurons separately generate repeated bursts of action potentials with irregular burst durations and interburst intervals and at a mean cycle frequency that is lower than the intact pyloric network rhythm. Thus, an important role of the strong electrical synapses between the AB and the PD neurons is to synchronize their inherent bursting activities with the more regular and rapid pacemaker activity of the AB neuron ( Bal et al., 1988 Abbott et al., 1991 ).

In addition to such a role in the synchronization of neuronal intrinsic oscillatory activities, experimental and modeling studies have shown that electrical synapses can regulate the frequency, burst duration, and variability of oscillations in ensembles of electrically coupled neurons ( Kepler et al., 1990 Sharp et al., 1992 Szucs et al., 2000 ). The regulatory control of oscillatory activity in a heterogeneous population of neurons has been investigated in a hybrid system in which an electronic neuron was artificially electrically coupled to in situ isolated PD neurons ( Szucs et al., 2000 ). The electronic neuron was then configured to generate either a periodic or an irregular bursting activity. In either case, depending on the coupling strength, the addition of an electrical synapse decreased the variability of the individual oscillatory activity and led to periodic oscillations in the neuronal ensemble. Concordant results were also obtained by using a computational model of two heterogeneous oscillatory neurons or in an experimental approach in which two isolated and oscillating biological neurons were coupled via an artificial electrical synapse ( Sharp et al., 1992 Soto-Trevino et al., 2005 ). Again in both cases, changes in strength of the electrical synapse controlled the regularity and frequency of rhythmic bursting in the coupled oscillators.

Therefore, electrical synapses not only simply synchronize activity within neuronal networks, but also exert subtle control over the variability and frequency of endogenous bursting or oscillatory properties of coupled neurons. Consequently, depending on electrical synaptic strength and the heterogeneity of the intrinsic membrane properties of coupled neurons, a given network can express complex and variable patterns of activity.


Turning Synapses Off

Once its job is done, the neurotransmitter must be removed from the synaptic cleft to prepare the synapse for the arrival of the next action potential. Two methods are used:

  • Reuptake. The neurotransmitter is taken back into the synaptic knob of the presynaptic neuron by active transport. All the neurotransmitters except acetylcholine use this method.
  • Acetylcholine is removed from the synapse by enzymatic breakdown into inactive fragments. The enzyme used is acetylcholinesterase.

Nerve gases used in warfare (e.g., sarin) and the organophosphate insecticides (e.g., parathion) achieve their effects by inhibiting acetylcholinesterase thus allowing ACh to remain active. Atropine is used as an antidote because it blocks ACh muscarinic receptors.


Lost In Transmission: How Much Electricity Disappears Between A Power Plant And Your Plug?

How much energy is lost along the way as electricity travels from a power plant to the plug in your home? This question comes from Jim Barlow, a Wyoming architect, through our IE Questions project.

To find the answer, we need to break it out step by step: first turning raw materials into electricity, next moving that electricity to your neighborhood, and finally sending that electricity through the walls of your home to your outlet.

Step 1: Making Electricity

Power plants – coal, natural gas, petroleum or nuclear – work on the same general principle. Energy-dense stuff is burned to release heat, which boils water into steam, which spins a turbine, which generates electricity. The thermodynamic limits of this process (“Damn that rising entropy!”) mean only two-thirds of the energy in the raw materials actually make it onto the grid in the form of electricity.

Energy lost in power plants: About 65%, or 22 quadrillion Btus in the U.S. in 2013

This graph shows the heating efficiency of different types of power plants. All types of plants have roughly the same efficiency, with the exception of natural gas, which has seen recent improvements in efficiency in recent years with the addition of combined cycle plants. (The coal efficiency line is nearly identical with nuclear energy, and is swallowed up in the purple).

Step 2: Moving Electricity – Transmission and Distribution

Most of us don’t live right next to a power plant. So we somehow have to get electricity to our homes. This sounds like a job for powerlines.

First, electricity travels on long-distance, high-voltage transmission lines, often miles and miles across country. The voltage in these lines can be hundreds of thousands of volts. You don’t want to mess with these lines.

Why so much voltage? To answer this question, we need to review some high school physics, namely Ohm’s law. Ohm’s law describes how the amount of power in electricity and its characteristics – voltage, current and resistance – are related. It boils down to this: Losses scale with the square of a wire’s current. That square factor means a tiny jump in current can cause a big bump in losses. Keeping voltage high lets us keep current, and losses, low. (For history nerds: This is why AC won the battle of the currents. Thanks, George Westinghouse.)

Jordan Wirfs-Brock / Inside Energy

The sagginess of power lines is actually the limiting factor in their design. Engineers have to make sure they don’t get too close to trees and buildings.

When that electricity is lost, where does it go? Heat. Electrons moving back and forth crash into each other, and those collisions warm up power lines and the air around them.

You can actually hear those losses: That crackling sound when you stand under a transmission tower is lost electricity. You can see the losses, too: Notice how power lines sag in the middle? Some of that’s gravity. But the rest are electrical losses. Heat, like the kind from lost electricity, makes metal power lines expand. When they do, they sag. Powerlines are saggier, and leakier, on hot days.

High-voltage transmission lines are big, tall, expensive, and potentially dangerous so we only use them when electricity needs to travel long distances. At substations near your neighborhood, electricity is stepped down onto smaller, lower-voltage power lines – the kind on wooden poles. Now we’re talking tens of thousands of volts. Next, transformers (the can-shaped things sitting on those poles) step the voltage down even more, to 120 volts, to make it safe to enter your house.

Generally, smaller power lines mean bigger relative losses. So even though electricity may travel much farther on high-voltage transmission lines – dozens or hundreds of miles – losses are low, around two percent. And though your electricity may travel a few miles or less on low-voltage distribution lines, losses are high, around four percent.

Energy lost in transmission and distribution: About 6% – 2% in transmission and 4% in distribution – or 69 trillion Btus in the U.S. in 2013

This graph shows the average percent of electricity lost during transmission and distribution, by state, from 1990 to 2013. With the exception of Idaho, the states with the lowest losses are all rural, and the states with the highest losses are all densely populated.

Fun fact: Transmission and distribution losses tend to be lower in rural states like Wyoming and North Dakota. Why? Less densely populated states have more high-voltage, low-loss transmission lines and fewer lower-voltage, high-loss distribution lines. Explore the transmission and distribution losses in your state on our interactive graphic.

Transmission and distribution losses vary country to country as well. Some countries, like India, have losses pushing 30 percent. Often, this is due to electricity thieves.

Step 3: Using Electricity Inside Your Home

Utility companies meticulously measure losses from the power plant to your meter. They have to, because every bit they lose eats into their bottom line. But once you’ve purchased electricity and it enters your home, we lose track of the losses.

Your house, and the wires inside your walls, are kind of a black box, and figuring how much electricity gets lost – electricity that you’ve already paid for – is tricky. If you want to find out how much electricity gets lost in your home you’ll either need to estimate it using a circuit diagram of your house or measure it by putting meters on all of your appliances. Are you an energy wonk attempting this? Let us know, we’d love to hear from you!

Energy lost in the wiring inside your walls: We don’t know! It could be negligible, or it could be another few percent.

The Future Of Transmission and Distribution Losses

Grid engineers are working on technologies like superconducting materials that could essentially reduce electricity transmission and distribution losses to zero. But for now, the cost of these technologies is much higher than the money lost by utility companies through their existing hot, leaky power lines.

A more economical solution to reduce transmission and distribution losses is to change how and when we use power. Losses aren’t a constant quantity. They change every instant based on things like the weather and power consumption. When demand is high, like when we’re all running our ACs on hot summer days, losses are higher. When demand is low, like in the middle of the night, losses are lower. Utilities are experimenting with ways to spread out electricity use more evenly to minimize losses.

The same principle applies to your house, which is basically your own personal grid. You can reduce losses in your home by spreading out your electricity use evenly throughout the day, instead of running all your appliances at once.

  • Generating electricity, we lost 22 quadrillion Btu from coal, natural gas, nuclear and petroleum power plants in 2013 in the U.S. – that’s more than the energy in all the gasoline we use in a given year.
  • Moving electricity from plants to homes and businesses on the transmission and distribution grid, we lost 69 trillion Btu in 2013 – that’s about how much energy Americans use drying our clothes every year.

Have an idea for an energy topic that could be fun in the classroom? Submit it below.

Related Series

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IE Questions

Energy is a broad and confusing topic. In this series, Inside Energy reporters de-mystify the wonkiness that dominates so much of the energy conversation, through answering your questions, as well as questions we encounter in the field. What's your energy head scratcher? Submit it at ask.insideenergy.org, e-mail it to us at [email protected], or tweet it to @InsideEnergyNow with hashtag #MyEnergyQuestion.

About Jordan Wirfs-Brock

Jordan Wirfs-Brock was Inside Energy's first data journalist, based in Colorado. Now she's living in the San Juan Islands, but is still helping us out. When she's not wrangling data, she enjoys running up and down mountains, doodling, playing board games and brewing beer.


How is a nervous impulse transmitted across a synapse?

A nervous impulse is transmitted across the synapse from a pre-synaptic neurone to a post-synaptic neurone through the use of neurotransmitter diffusion. To explain this in more detail let’s take the example of a cholinergic synapse a synapse that uses the neurotransmitter Acetylcholine. The transmission across a cholinergic synapse can be summarised in 10 steps: 1. Firstly, an action potential (change in electrical potential) arrives at the pre-synaptic neurone. 2. This changes the voltage in the neurone causing the voltage-gated calcium channels on the pre-synaptic neurone to open. 3. Calcium ions then diffuse into the pre-synaptic neurone. 4. The increased concentration of Calcium in the neurone then causes synaptic vesicles, containing the neurotransmitter acetylcholine, to move towards the membrane on the pre-synaptic neurone. 5. The vesicles fuse to the membrane and the neurotransmitter is released into the gap between the two neurones (known as the synaptic cleft). 6. The acetylcholine neurotransmitter then diffuses across the synaptic cleft towards the post-synaptic neurones membrane. 7. Here, the acetylcholine neurotransmitter then binds to the complimentary receptors on the post-synaptic neurone’s membrane. 8. The increase in concentration of the neurotransmitter causes ligand (chemical) gated sodium channels in the post-synaptic neurone membrane to open, allowing sodium to diffuse into the post-synaptic neurone. 9. The increased concentration of sodium ions now in the post-synaptic neurone depolarise the neurone’s membrane causing EPSPs (excitatory post-synaptic potentials). 10. If these EPSPs reach a certain threshold, then an action potential is initiated in the post-synaptic neurone and the impulse has been successfully transmitted from one neurone to the next! If you can remember these 10 steps then you can thoroughly explain transmission of a nervous impulse across a synapse. To help you remember these steps try making a poster showing the process visually, or perhaps try creating a mnemonic.


Hydraulic Transmission

Hydraulic transmission is a transmission method that uses liquid as a working medium to transfer energy and control.

  • From the structural point of view, the output power per unit weight and the output power per unit size is force-compressed in the four types of transmission modes, and have a large moment inertia ratio. The volume of the hydraulic transmission is small when the same power is transmitted. Light weight, low inertia, compact structure and flexible layout.
  • From the performance point of view, speed, torque, power can be steplessly adjusted, fast response, fast commutation and shifting, wide speed range, speed range up to 100:1 to 2000:1 fast action, the control and adjustment are relatively simple, the operation is convenient and labor-saving, and it is convenient to cooperate with the electrical control, and the connection with the CPU (computer) to facilitate automation.
  • From the point of view of use and maintenance, the components have good self-lubricating properties, easy to achieve overload protection and pressure keeping, safe and reliable components are easy to achieve serialization, standardization and generalization.
  • All equipment with hydraulic technology is safe and reliable.
  • Economy: The plasticity and variability of hydraulic technology are very strong, which can increase the flexibility of flexible production, and easy to change and adjust the production process. Hydraulic components are relatively inexpensive to manufacture and have relatively high adaptability.
  • Easy combination of hydraulic technology with new technologies such as microcomputer control constitutes the “machine-electric-hydraulic-light” integration, which has become the trend of world development and is easy to realize digitalization.

Everything has two sides, there are advantages and disadvantages. Hydraulic drives are no exception:


Watch the video: Εκπαιδεύοντας τους σκλάβους του μέλλοντος (September 2022).


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