Neurons would need energy to generate those pain 'signals'

[mtc1973]

:) I had you pegged for knowing that that was BS already..

 

[Bararontok]

Sodium ions are not there for increasing conductivity. These are not your chemical electrolyte solutions where we have passage of electric current between battery ends. They are their to increase or decrease membrane potential.

Energy from the stimuli (as far as I know) cannot and is not used for any impulse generation.

It says in this source that the membrane potential is a voltage and that the cells function as batteries. Because what is potential but a difference in charge that allows electrons from a region of higher voltage to migrate to a region of lower voltage?

http://en.wikipedia.org/wiki/Membrane_potential

These other sources also say that the sensory receptors convert the input energy of the stimuli into electrical impulses.

http://en.wikipedia.org/wiki/Sensory_receptor

http://en.wikipedia.org/wiki/Sensory_transduction

 

[mtc1973]

The membrane potential is a voltage, no one disputes. But they are not like a battery and wire configuration with charge moving round the circuit, think more like a mexican wave in a stadium a propagating wave of local charge movement across the membrane.

 

[mtc1973]

As for the second bit - receptors do transmit some albeit very little energy in the form of chemical energy. But they are not the source of the energization of the action ppotential. The whole system is an energy continuum, energised by the ion pumps once we get to the action potential. But there is nor sufficient energy in a receptor ligand interaction alone to energise and maintain an action potential. I think that perhaps this is not what you meant, but I and others thought that you were under the impression that the energy from the binding if ligand to a receptor was the driving force for an action potential. When in fact it is the initiator not the energiser. Think starter motor not engine.

 

[Borek]

As for the second bit - receptors do transmit some albeit very little energy in the form of chemical energy.

Quote post you are answering to, it is not clear what you refer to.

 

[mishrashubham]

It says in this source that the membrane potential is a voltage and that the cells function as batteries.

Whenever you cite a source please mention exactly where the statement that supports your claim, lies.

Because what is potential but a difference in charge that allows electrons from a region of higher voltage to migrate to a region of lower voltage?

http://en.wikipedia.org/wiki/Membrane_potential

These other sources also say that the sensory receptors convert the input energy of the stimuli into electrical impulses.

http://en.wikipedia.org/wiki/Sensory_receptor

http://en.wikipedia.org/wiki/Sensory_transduction

Just like mtc1973 said, energy from the stimulus is used as an ignition after which the energy used to carry signal forward is given by ATP; just like an engine where the combustion is started by a small spark which can be said to transfer energy bu to keep the combustion going on you need fuel.

 

[Bararontok]

Yes, I did not say that the energy of the stimuli alone was the cause of the transmission of the signal. I even mentioned that the energy is merely used to switch on the transmission and not to power it.

I even mentioned that here:

The energy of the stimuli may be what generates the initial electrical impulse but the other processes that ensure that information is constantly fed to the brain draws energy from the body itself.

 

[mishrashubham]

I still need thee information from the sources though.

 

[Pythagorean]

I still need thee information from the sources though.

most of it's really in the transduction article, since that's the mechanism of stimuli conversion: 'transduction".

Transduction in the nervous system typically refers to synaptic events wherein a mechanical/physical/etc stimulus is converted into an action potential which is transmitted along axons towards the central nervous system where it is integrated.

For example, in the visual system, sensory cells called rod and cone cells in the retina convert the physical energy of light signals into electrical impulses that travel to the brain. The light causes a conformational change in a protein called rhodopsin. This conformational change sets in motion a series of molecular events that result in a reduction of the electrochemical gradient of the photoreceptor. The decrease in the electrochemical gradient causes a reduction in the electrical signals going to the brain. Thus, in this example, more light hitting the photoreceptor results in the transduction of a signal into fewer electrical impulses, effectively communicating that stimulus to the brain.

(emphasis added)
It's a wiki article with no references, but it conforms to my general understanding from my neurobiology course and the basic idea that the stimuli isn't an energy source, but a kind of "switch". Though "switch" is oversimplified, really. The more interesting receptors are actually resonators rather than integrators. That is, they respond to particular phases/frequencies of stimuli, not a simple threshold value (for instance, the hairs cells in your ear).

 

[mishrashubham]

most of it's really in the transduction article, since that's the mechanism of stimuli conversion: 'transduction".


(emphasis added)
It's a wiki article with no references, but it conforms to my general understanding from my neurobiology course and the basic idea that the stimuli isn't an energy source, but a kind of "switch". Though "switch" is oversimplified, really. The more interesting receptors are actually resonators rather than integrators. That is, they respond to particular phases/frequencies of stimuli, not a simple threshold value (for instance, the hairs cells in your ear).

Thank You Pythagorean

 

[thorium1010]

Yes, I did not say that the energy of the stimuli alone was the cause of the transmission of the signal. I even mentioned that the energy is merely used to switch on the transmission and not to power it.

I even mentioned that here:

The energy of the stimuli may be what generates the initial electrical impulse but the other processes that ensure that information is constantly fed to the brain draws energy from the body itself.

The means by which a neuron carries a signal is depolarization , read about depolarization.
http://en.wikipedia.org/wiki/Depolarization"

http://en.wikipedia.org/wiki/Action_potential"

read about action potential.

Its not so much as a electrical signal, rather depolarisation of membrane potential that carries the signal along the nerve.

The initial stimulus if crosses a threshold is able to depolarize the membrane of nerve which further leads to depolarization along the nerve propagating as a signal. This is energy dependent (ie atp) since energy is required to maintain the membrane potential.

 

[Bararontok]

This is quoted directly from the source:

http://en.wikipedia.org/wiki/Depolarization

Because depolarization is a change in membrane voltage, electrophysiologists measure it using current clamp techniques. In voltage clamp, the membrane currents giving rise to depolarization are either an increase in inward current, or a decrease in outward current.

So the depolarization process is what performs the switching action that permits current to flow. Because if two potentials are of equal and like voltage, their forces will cancel out and no electrical current can flow, but if one end of the nerve line has a lower or opposite polarity for voltage, then the region of higher potential will induce a current which will travel to the region of lower potential, thus causing a flow of electrical current.

 

[mtc1973]

Baron - there still seems to be some misunderstanding. Current does not flow down a nerve. The potential us not set up between one point On the nerve and another, it is set up across the membrane. I am by the way an electrophysiologist and have spent years patch clamping doing whole cell measurements, you just need a basic physiology textbook - and some time to get this correct. These wiki articles you quote are quite fine but there seems to be a fundamental misunderstanding on how an impulse us generated and maintained. I'll dig out a good source tomorrow and post.

 

[mtc1973]

In the upper laft (sorry I couldn't post the pic had to attach) this is resting state. The iside of the axon is net negative charge and the outside net positive - largely due to the fact that K channels in the membrane are open and holding the membrane potential at a negative value (i.e. K initially leaves the cell - leaves the inside net negative then K flux stops at the membrane potential is generated and balances the K flow). This is all energized by the Na K ATPase - which is burning up ATP by the minute keeping the K gradient - this is where the energy is consumed! So without even initiating a nerve impulse we are burning up energy constantly. Na channels in the membrane are then triggered to open by some external stimulus (like pressure at a pressure transducer in the skin), leading to Na coming into the cell - and since it is a positive charge the cell interior now has a positive charge (outside negative), i.e. the membrane potential has changed. This actual flow in terms of amount of ions though - is tiny, very small indeed. i.e. only a few million ions need to flow to change the membrane potential at that point (this is minuscule compared to the standing ion gradinets - which is why there is no great energy consumption to correct this ion flux - the background energy consumption of keeping the huge concentration gradient in the first place outweights tiny amount of Na that comes into the cell - and will then have to be pumped back out). This change in membrane potential as Na comes into the cell - is sensed by other Na channels and they too open. The Na channels remains open for a very short duration and then automatically closes. So this wave of depolarization is what travels along the axon - but in no way does charge flow along the length of the axon. It is a traveling wave of local depolarization. Any good physiology textbook will cover it in detail. Sorry for the delay.

And remember - the main energy consumtion comes from setting up the K gradient and Na gradient in the first place. Not by the passing of the action potential. Hence there is a huge resting cost to keep membrane potential but a fairly insubstantial cost to actually then use that stored energy. Think of it like a battery on constant charge - and then we use a little of the battery power and then switch it straight back to charge again. You power consumption comes from the charging - not the battery usage.

 

[jackson6612]

MTC, did you scan the drawing or draw it on the screen? Just curious to know.

 

[mtc1973]

Pencil paper and scan.

 

[jackson6612]

Thanks for letting me know.

 

[Bararontok]

So in conclusion, the signal is propagated by the constant depolarization from one cell to another and this is what allows the electrical signal to travel through the neural network. The energy of the stimuli opens the channel for the sodium ions which will flow out, change membrane potential, and cause a voltage to flow between two membranes due to the potential difference before the sodium ions then flow to another cell membrane. Thus the flow of electrical impulses is intermittent since it can only flow between two membranes while it is the current of sodium ions that permit this short range transmission of signals to travel a long distance through the neural network.

 

[sameeralord]

I think you have to consider adaptation as well. When a stimulus of constant strength applied and maintained on a receptor, the frequency of the action potentials in its sensory nerve declines over time. Can anyone tell me how this occurs.

 

[mtc1973]

Experimentally you can demonstrate adaptation. If you trigger an action potential by eg a 20 mv depolarisation of membrane potential. Now if you do say 2 or 3 smaller pre depolarizations and then do 20 mv depolarisation as you initially did then you no longer see an action potential. The reason is that chronic depolarisation even if quite small causes the sodium channel to go into a locked closed configuration - so no further action potentials are possible. There are also mechanisms by which the receptor system itself can accommodate, those will be specific to the specific receptor system involved.