Nervous system signals and their implications

Paul Grobstein's picture

Welcome to the on-line forum associated with the Biology 202 at Bryn Mawr College. Its a way to keep conversations going between course meetings, and to do so in a way that makes our conversations available to other who may in turn have interesting thoughts to contribute to them. You're welcome to post here any thoughts that have arisen during the course this week (and to respond to thoughts others have posted).

Some issues worth exploring this week are the implications of thinking of the nervous system, and behavior, in terms of action potentials, receptor and generator potentials, and synaptic potentials.  What does this help to make better sense of?  What does it seem difficult to account for this way? What new questions does it open up?  

evanstiegel's picture

I believe that the idea of

I believe that the idea of action potentials, receptor and generator potentials, and synaptic potentials somewhat trivializes (word choice??) how we experience the world around us.  Turning everything that we see, hear, touch, and smell into light waves, vibrations, and chemicals takes away from my life experience.  Even though our I-function creates a new experience into what we know these waves, vibrations, and chemicals as, knowing what really goes on isn't too comforting. 
Shelley's picture

sociopaths and the conscious

My name is Shelley and I go to ventura College in California. I'm taking a physiological psychology class and we discussed the conciousness in sociopaths and I was wondering about raising anxiety levels with gaba and if you know of any studies on this to give sociopaths (murderers) a guilty concious. My question is, "Can you treat sociopaths with Gaba and if it has been done what were the results?"

Thank You,
Shelley Lehmann

Serendip Visitor's picture

Conscious

You're a college student taking courses in psychology, and you don't know the difference between "conscious" and "conscience"? Maybe you should start there before going any further.

Serendip Visitor's picture

more about antisocial

This person is not antisocial in the way that they would every harm anyone outright. They are very volatile and such but mostly in social ways, and ways that would do emotional or monetary damage or whatever. I wanted to add that and to say that most antisocial people are not overtly dangerous in that sense. I don't understand it but I am desperately seeking help for someone who has fallen ill to this chemical imbalance. I know it is chemical. There are other things that I am looking into and they are varied as far as antisocial medication supplements go. So please. If you are very very serious about this disorder please contact me. I dont usually ask to be contacted but when I saw the heading about gaba I just knew whoever wrote it was serious and intuitive regarding this disorder. Whoever they are sure could become a doctor or psychologist. very astute.

Serendip Visitor's picture

yes it works

yes yes and yes. i found this info looking online because i noticed it works. It is not a complete therapy but is halfway there and could be enhanced etc. It causes the antisocial person to have more worry for some reason. They are very cognizent and afraid of the way it makes them feel, but all in all, it makes them normal. period. it is not a therapy yet, but is very very promising as an adjunct or whatever. I need to find something and soon for someone. Please contact me if you have more answers especially about gaba benzodiazapenes 5-htp etc. i can leave my email and then my number to anyone who is looking seriously into this.

heather's picture

perception

synesthesia is such an intriguing phenomenon because it opens up the idea that others may perceive the world in an entirely different way than you, the individual. it reminds us (well, me at least) that, for example, what i perceive as "red" may not look at all the same to any other individual, and i would have no way of knowing otherwise. we all have the same name for what we are seeing, but have no quantitative or substantial way of comparing what we are actually seeing.

oh how i love that we cannot know.

PS2007's picture

The class discussion and

The class discussion and some of the posts on the forum also reminded me of synesthesia. I wish there was some way we could know how other people percieve colors. I found an interesting website that tries to illustrate how Vladimir Nabokov saw the alphabet (he had synesthesia). I thought this was very interesting.

http://www.gingkopress.com/_cata/ima1/alco-0.htm

 

K. Smythe's picture

Consciousness etc.

I thought the discussion about consciousness we had in class was really interesting.  In writing papers over the years i've always made the generalization that -people like to believe they have free will or consciousness or some sort of over-arching control.  However i'd never really thought about how i felt regarding this subject.  I realized that i'm not sure it's important that we have some sort of control over our nervous system/bodily functions.  Having consciousness (or my perception of it) is great, but i'm sure i'd get along just fine and would still have a rewarding (though different) life if i didn't have it.

 On the topic of consciousess it is also interesting to think of our experiences of consciousness as subjective.  It is a strange concept to realize that we only "know" that other people have consciousness because we do, and we believe that others experience as we do.  It's kind of like the concept of sensory perception (and or synesthesia)-how we can only guess that our perceptions of colors, tastes and touch are the same as those around us.

 

 

eambash's picture

Randomness?

I'm rather glad to be discussing the idea of the action potential and the ways that signals and responses actually interact.

I've had some trouble picturing the nervous system in terms of analogies (since, as a humanities major, I tend to start from details and move towards an image, not the other way around). However, when I compare this analogy to all the other things we've been talking about and the other images we've looked at -- the leech nervous system's independent responses, the anatomy of the brain, the parts of a neuron -- I do find it quite useful. I have been wanting a way to account for the fact that there seems to be a gradient of responses and levels of response. Sometimes reactions to stimuli don't seem that great, and sometimes things happen without any stimuli but seem much more obvious externally.

I appreciate rdelacruz's concept of a line of batteries connected to one another. To me, it's very helpful to picture multiple batteries, since, even with the I-function, I still tend to picture neurons as independent input/output boxes and to forget to look at the box that boxes them ALL in. At any rate, what I want most right now is a clearer explanation of how or why signals can start from inside the nervous system. Since all the neurons are connected to some degree, can we not still say that the outside (stimuli) has some effect?

Skye Harmony's picture

conscious/conscience

I’m interested in the idea of a conscience, and I wonder how it relates to having an I-function. We seem to have defined the I-function as consciousness, that is, being aware of ourselves and being able to think and know that we are thinking. I think about having a conscience in the same way as Maggie: you’re used to it and find it kind of nice if you have one, but you don’t care if you don’t have one. I think about consciousness in this same way- it’s impossible for me to imagine what it would be like to be unaware of myself, but if I weren’t aware, I wouldn’t be able to think that. But I don’t think consciousness and having a conscience are the same thing. In fact, I think that having a conscience requires someone to be conscious (have an I-function), but being conscious does not necessarily mean you have a conscience. (Sorry, I hope this is not confusing, I wish the two words were not so alike!) For example, all humans should have an I-function unless they have a severe mental defect. But how about sociopaths- they don’t seem to have a conscience. They seem to be aware of their actions, but they don’t seem to understand or care about whether their actions are good or bad for other people. What IS the conscience? Is it a “box” connected to the I-function that helps us evaluate our actions? Or is it just a construct we came up with and not localized in the mind?

 

Do nonhuman animals have an I-function? And do they have a conscience? They seem to be able to learn the difference between “right” and “wrong.” My dog gets a guilty look when he has done something “bad” like eating candy. But perhaps this is anthropomorphization and they just learn humans’ reactions to their behaviors and they know that they will be rewarded or punished based on specific behaviors.

 

On a slightly different note, I also wonder what role feelings and emotions play. Has anyone else seen the movie “Equilibrium?” I thought many parts of it were unrealistic but it raised a lot of interesting questions for me. It’s about a creepy future in which everyone is forced to take a drug that suppresses emotion and feeling. One problem I had with the movie is that the characters still seemed to have personalities and be somewhat attached to each other when they supposedly couldn’t feel, but the main character has to start feeling before he gains what I recognize as a conscience. It seems to me that emotions are necessary for personality and attachments to other people. I guess I am just wondering if emotion is part of the I-function, something that comes about because of it, or independent of it. How are emotions, the conscience, and consciousness related? What causes each person to be a unique individual? (Obviously there are biological differences, but do they affect the person’s I-function, or what?)

nasabere's picture

Zero input yeilds output and our battery model...

I'm so perplexed; my confusion lies in the notion of zero input yielding outputs. It would seem that an action potential, which ultimately yields some response, can only by initiated by a depolarization in the axon membrane. Maybe I’m missing something major here, but shouldn’t it follow that something—perhaps some input—must be present in order to generate a change in membrane permeability, and thus a subsequent output? I guess what I’m really asking is this; when, where, and how does the whole process start if such a phenomenon as “zero input” exists? I’m having a difficult time understanding how a membrane at resting potential can spontaneously alter its permeability and generate action potentials without any sort of input. For this reason, I’m inclined to think of nervous system communication as a series of ever-perpetuating action potentials, where at no instance can an action potential arise without some sort of stimulus—even when it appears that “zero input” yields an output, an input may indeed present.

Someone please enlighten me...

Skye Harmony's picture

zero input?

I think the idea of zero input meant that there was no input from outside the nervous system. So the input could come from somewhere within the nervous system (one of the smaller boxes within the larger box) and end up creating an output. That being said, I'm not exactly sure what would trigger this... maybe chemicals in the brain influciencing neurons? But would that be considered external input? I am also confused about this topic... hopefully we will discuss it more in class.
nasabere's picture

I thought

I was under the impression that our previous discussion on inputs and outputs was not limited to external inputs but rather, encompassed ALL inputs. Isn't input just that, regardless of where it came from? I'm curious; how would you define internal and external input? I haven't really thought of inputs in such a rigid way, but in retrospect, I suppose that my assumptions were that all inputs were external to the neuron. Again, I ask where exactly does an action potential start? Within a neuron or externally? hmm...

Thanks for your thoughts!

merry2e's picture

Myelin, Action and Conscious/Conscience, I think covers it...

 

Another site to view an action potential…

http://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swf

I really find myelination fascinating, especially in regards to the different types of medical conditions and associated behavioral changes demyelination can have on the body, severely slowing down action potentials or completely halting them. . In respect to the topic of action potential and myelin, after reading over a couple of chapters in Principals of Neural Science (Kandel, Schwartz, and Jessell-this book has been very useful for me and I highly recommend it!) in regards to conduction of an action potential, my understanding is that depolarization is one of the primary mechanisms controlling conduction, which is affected by:

·         Capacitance-higher rates slow down conduction of signals

·         Axial resistance -“axons with the largest diameter have the lowest threshold for extracurricular current. The larger the diameter of the axon, the lower the axial resistance to the flow of longitudinal current because of the greater number of ions per unit length of the axon” (146).

Another important factor is ion channels involved with resting potential break down the signaling capacity of the neurons, which can delay the action potential and reduce the distance a signal can move.

Ok, I have no idea…I was jotting down notes as I was reading and don’t know if I got it, but have a lot of stuff swirling around in my BRAIN…

 

Philosophical notes…what type of consciousness are we talking about?? Are we as human beings really that more conscious than birds or bears, for instance? A bird makes a nest, knowing it is the season to lay its eggs, looks for the materials to makes it nest, than after laying her eggs, keeps them warm until they hatch. If humans or other animals come into contact with the eggs or babies, she will not go back to them. Are these conscious decisions, flight or fight responses, etc? Are we more conscious when there are genocides in Darfur, Rwanda, DRC, and in our own back yard going on every day and we turn our heads? Just a thought…

Kandel, Eric R., James H. Schwartz, and Thomas M. Jessell.  Principles of Neural Science.  McGraw Hill,  2000.

cheffernan's picture

Still a little unsure

Like most of my other classmates, I also sturggled with trying to understand action potentials as a battery and not thinking of them in terms of electricity. Zoe made a good point that batteries provide electricity so it is hard to not associate the two, but my struggle in understanding comes from my inability to forget what I have previously learned in other courses. It makes sense considering how Professor Grobstein asked us to question all truth, to question what we already learned as truth as well.

I understand trying to relate such a complicated system as the nervous system to something with which we are all familiar with, in this case the battery and previously with the Input/Output Box Model. While at the same time, I still find it hard to try to form a model with the same processes. For example the movement of ions, it is hard to replicate the electromagnetic-concentration gradient established along the axon. I am interested to see how the battery self stimulating will be related to the "I function" and look forward to finding this out on Tuesday.

llamprou's picture

I would like to answer

I would like to answer maggie's, question as to why at least I feel as though it is better to have a concious that not to have one. I believe that everything that one does is governed by ones concious including what is right and what is wrong. Without a concious i feel as though i would be more inclined to do things that were mean or unkind. Perhaps this is silly and the concept of concious was actually created to make people believe that one existed to prevent wrong doing. But i have been raised to believe that a jimminy cricket does exist inside everyone. Often times i do not do the right thing because i know others will percieve it to be so, i doo it because i feel that if i do not do the right thing my own personal jimminy cricket is going to get worked up and then guilt sets in. Knowing you have a concious is what in one way or other makes us human, unable to treat others badly.... the ability to tell the truth... I do not know if this makes any sense but this is at least what i believe.
Sophie F's picture

Wow.

I’ve thought about this a lot and read the thoughtful comments of the people who posted before me. I am still having some trouble conceptualizing the way in which this battery-operated system works.

So, back to the idea of random movement of ions… It makes sense that random movement occurs, based upon Professor Grobstein’s explanation of ion concentration within and outside a neuron being a statistical phenomenon. Extrapolating the idea of randomness from the microcosm of signal transduction to the effect of that random movement, namely outputs without inputs, for me begs a question: what sorts of outputs result from this random movement? Are they visible (to an observer) behavioral outputs? Are they autonomic processes of which we are not aware that mediate physiological processes? If no two brains are alike, and each brain capable of myriad cables connected to boxes, connected to other boxes… are some organisms more susceptible or likely to experience outputs without inputs? Is there some sort of “potential” energy stored that initiates the turning “on” of the battery?

Rica Dela Cruz's picture

I was confused about the

I was confused about the analogy of the battery and the action potential when first introduced to the concept, yet I have come to understand it more after thursdays class. I do not like the idea of each action potential being like a flashlight turning on and off from a battery. Although it makes sense that the action potentials do turn on and off along an axon, it does not make me think of the action potential as a battery, but as multiple flashlights run by batteries along an axon. It is easier to think of an axon being a line of batteries where an action potential is produced when the positive end of a battery meets the negative of another battery. The electric current moves along the line of batteries, producing action potentials when crossing to a different battery, until it reaches the end and lights the flashlight. For me, the flashlight turning on in the end seems analogous to the action potential reaching a target neuron such as a motor neuron. I do not know if this makes sense to anyone else or how others would feel about this way of thinking though. 

The explanation of Erwin Schrodinger's theory helped me understand diffusion a lot more. I have learned it before, but never really thought about it as much as we did in class. It cleared up some questions I had about depolarization and hyperpolarization.

I think it is interesting that molecules moving randomly can depolarize a membrane and produce action potentials allowing for actions when I actually do want to produce an action. This makes me wonder how these ions know when to depolarize at the right time when I want to move or feel. It is because they are constantly depolarizing and the reason I do not produce an action is due to the action potential not reaching a target neuron? Is there something coming from the nervous system telling the ions to depolarize or not?

 

Madina G.'s picture

Myelin and thoughts on "lightening and thunder"

The battery analogy, I feel, is both great at explaining particular aspects of action potentials yet lacking in other areas. There's no better way to imagine the electrical gradient across the membrane that provides the means by which a depolarizing effect can take place, than to picture a battery, the voltage source in a complete circuit. This is all very good for the purpose of simplifying the mechanism by which action potentials work in order to understand it more clearly, however it is difficult to refer to this model to account for other properties belonging to action potential propagation. One of the most notable factors in this process is myelin, a component of the neuron required for rapid propagation and is required for effective conduction of electrical signals. I don't recall an analogous insulating feature in the battery analogy that makes the effective propagation of action potentials possible, although I may be wrong.

On a different note, I found the hearing thunder and seeing lightening concept Prof. Grobstein brought up really intriguing although I would like to hear more clarification on that topic. Can the idea of proper wiring, that is the correct connection of input and output boxes when all of the action potentials throughout the body are the same, explain some disorders such as dyslexia, where the input results in a different output from those who suffer from the disorder? If so, since this can be remediated to a certain extent via therapy and training, is this an actual rewiring of the input-output connection?

jchung01@brynmawr.edu's picture

consciousness

doesn't conscience have to do with hormone levels in the body? which is probably why we have different responses everytime and different intuitions because of different chemicals reacting with the simple input.

 

maggie_simon's picture

Thoughts on the "I-function" discussion in Tuesday's class

These are just some thoughts from Tuesday’s class, in no particular arrangement:

The idea that the mind does not have complete control over the body: Why does the mind need to feel like it is the center?

Why do we say that what we think takes precedence over the sensations that we feel?

Do we keep thinking above physical sensations because it helps to separate us from other animals (because we cannot enquire of them whether they are conscious or not, although if consciousness comes from the neo-cortex, then we are no longer separated from all other animals)?  Do we need to be separate from other animals so that we can survive (that is, so that we don’t over think moral implications of killing them for food…)?

 

 

I found it very interesting that when asked whether they would prefer to have a conscience (as opposed to not having a conscience) most of the class raised their hands.  I would be interested in hearing some reasons why.  My thoughts on the matter are that it doesn’t matter either way.  If you have a conscience, you might miss it if you knew that you had to live without it; on the other hand, if you don’t know what you are missing…  I guess that the way that I have expressed my view here illuminates an assumption I seem to have: that having a conscience is somehow better than not having one.  I think perhaps this is because I associate having a conscience or consciousness with meaning, and so gives life a significance, which perhaps is only necessary for those organisms with an “I-function” (if the “I-function” truly serves the purpose that we discussed in class associated with conscience); I assume that it is not a concern to those without because it never comes up in thinking. 

EB Ver Hoeve's picture

Persian Rugs

Like Anna, I understand the analogy, and I can see how it can be useful in understanding how the brain works. Last week, the New York Times had an article about migraines that seems to be particularly relevant for this discussion. Oliver Sacks, a neurobiologist who is familiar with visual migraines from childhood, describes the “aura” just before the migraine arrives, attempts to articulate the visual images that appear as the migraine is occurring, and then offers insight into what he believes causes migraine images. He discusses the symptoms, the implications, and possible revelations of visual migraines in relation to the brain itself.

“These geometric and scrolling motifs seemed somehow familiar to me, though it did not dawn on me until years later that this was because I had seen them not only in my environment but in my own head that these patterns resonated with my own inner experience of the intricate tilings and swirls of migraine.”

Could it be that stimulation in the brain generates action potentials that show up as these complex geometrical patterns that expose the crystalline structure of our consciousness? Could these visualizations not only be coming from the brain, but also in fact, be visions of the brain? I think the action potential idea is a fascinating way to think about this. To answer these questions, I am planning to read one of his books.

For more on this topic, see http://migraine.blogs.nytimes.com/2008/02/13/patterns/
I.W.'s picture

Constructing the Persian Rugs

I have had visual migraines since I was a child and it has always been a quest of mine to find out where they fit in.  As if by putting them in a category with other senses or neural functions I would be able to just get rid of them.  But recently I have begun to think of it in the exact opposite way. The last line of the article you posted struck a cord with me:

 

“In this sense, the geometrical hallucinations of migraine allow us to experience in ourselves not only a universal of neural functioning, but a universal of nature itself.

 

Or as you put it they are “visions of the brain” not just from it.  Auras no longer seem to be simply a neurological error; they are a constant reminder that even our own brains are so far beyond our understanding.  We try and put all of these different functions into their own category and file them away, but I think it is much more interesting to think of it all without boundaries. Action potentials are the basis of it all.  Our neurons are firing and creating a whole world for us.  That is why I dislike the analogy of action potentials as a battery.  To place those two things side by side makes us think that neurons are nothing more then a wire and the action potentials as nothing but electricity running through it. But there are so many neurons functioning so seamlessly to form our world, that a battery degrades them. It is the errors like auras that remind me how constructed the whole world around us is, and how well our brains do their job (normally). 

 

Margaux Kearney's picture

Action potentials cont'd

I thoroughly enjoyed our class discussion thursday about action potentials and how they can be compared to batteries. I've only taken Intro Bio so far, so I only had the perception that action potentials were electrical impulses that traveled down an axon from one neuron to the next. I never even considered electricity traveling the speed of light, so i didn't know that this concept was incorrect with respect to action potentials. I didn't ask to observe any summaries of observations!Seeing that my view of action potentials has changed, what about chemical impulses (message traveling from one neuron to the next via synapses)? Is there an analogy for them? Are they "chemical impulses" or is that incorrect? Also, this has been bothering me for a while: a battery does not last forever unlike electrical outputs that provide electricity to electronical devices. Could this loss of "power"( battery running out) be compared to the strength of an action potential down an axon? from one neuron to the next?
Jessica Krueger's picture

I'm wondering

Where topographic organization fits into this discussion?

 

If sensation is the product of a pattern of outputs, but this pattern is the result of several identitcal action potentials traveling along cables at a measurable (and relatively slow) rate of speed, would topographic organization affect how this information is perceived?

Olfaction is considered one of the most "direct" senses in that it does not pass through the thalamus during processing (1). Yet we humans seem to dedicate so little attention to olfaction that we don't even have a very profound or insightful vocabulary to describe scents, (2) with one text even describing the sense of smell as "much less essential than vision or audition..." (3). Our primary sensations are routed through the thalamus, meaning it takes more cabling, and conceivably more time, to perceive what we see or what we hear. What does this mean for our experience of the world? Why do the things we see and smell coincide? Why don't we smell well in advance of seeing things in front of us?

1. Olfaction and the Brain, Brewer Castle & Pantelis

http://books.google.com/books?id=UM_A_FDe8lkC&printsec=frontcover&source=gbs_summary_r#PPA70,M1

"Encoding of olfactory stimuli in relation to semantic processing and affect."

2. Physiology of Behavior, Carlson

Chapter 7 Audition, the Body Senses, and the Chemical Senses: Olfaction

Pg 238

3. Olfactory Pathways and the Limbic System

www.neuroanatomy.wisc.edu/coursebook/neuro3(2).pdf

Emily Alspector's picture

different perspectives

I will admit that when we were discussing batteries and then turned the discussion to membrane permeability, I was thrown off and thought the two had very little to do with each other. Then, just as class was ending, everyone was neatly tied together and it really did help my understanding of action potentials in a way I had never thought of them before. I have taken Intro bio and other NBS-related courses, but I had never been given the opportunity to look at an action potential in such a relatable way.

When we were talking about I-functions and motor memories like not being aware of your movements when walking or driving, it got me thinking of another class I took about cognition and how a lot of times we make mistakes, for example, walking out of the room and turning on the light, just out of habit, but not realizing before you complete the action that the light wasn't actually on. This seems like a misfiring between I-function and our motor outputs. I'd like to discuss how this (and other similar examples) could be further theorized.

I also would love to talk more about action potentials and how they relate to input/output systems, since it seemed the conversation was cut off at the end of class. Someone brought up epilepsy, and I think it would be interesting to look at an epileptic seizure in terms of these input/output boxes because even when there "is no input", I still think there is something triggering the nerves internally from within the system, and I think epilepsy would be a good way to revisit that conversation.

mcrepeau's picture

Perpetual Propagation Machines and Energy

The first rule of thermodynamics is that "energy can neither be created nor destroyed", but is instead continuously reallocated, to the ground, to the air, from one organism to another, from one atom to another; all life, it would thus seem, is one giant game of pass the potato, the "god-machine" a giant perpetual motion device of which all materials of existence are apart. This is true of all energy whether chemical, or electrical. We have spent a good deal of time discussing what an Action Potential is like and how one can manipulate its propagation, and pondering how one identical signal can produce an infinite number of outcomes. In class we have discussed how an action potential can be "passed" on from one battery to another, but we have not yet discussed where the action potential (the very first one in the line of propagation), in terms of the energy that it is, comes from. What initiates the first action potential in an axon (changes in membrane potential due to the presence of neurotransmitters?--what of the very first axon to generate the action potential---how do the sensory neurons in the eye for example generate an stimulus induced action potential---what in the stimulus triggers the depolarization of the cell?), where does this source of energy come from. It must already be there somewhere in the cell and in the body, from the food we eat to the cells perhaps, but in other instances, such as the beginning of embryonic development the initial depolarization that sets the whole process of creating you (the first spark of energy taken in--the first change in cellular potential) does not hail from a dietary source, or even from a nervous system, but from the depolarization and change in membrane potential of an egg cell by a sperm cell---are we then, when philosophizing in terms of action potential = energy, somehow continuously propagating these initial potential changes throughout our lives, are we then (since the catalysis for these energy changes came from our parents) perpetuating an action potential of some kind from our parents, from our ancestors?

Angel Desai's picture

Some more action potential and battery business

I think the main reason that I have had difficulty thinking of action potentials as batteries is because the concept of the "battery" itself connotes a physical object that resides somewhere "within" the nervous system. The action potential as it exists however, is not technically an actual object which can be picked up the same way a battery can, however perhaps it is just the idea of what the battery does that is important in sustaining this analogy.

In thinking about the above, I also remembered something we talked about in class on tuesday-the idea that the action potential as a battery successively turns on and off moving along an axon. This description or belief, as I understood it, accounts for reaction times-but this suggests that action potentials are similar each time they are generated. What then, accounts for experience-for example, in Intro Bio we performed a lab that measured reaction times for certain activities, however I found that with practice over time, my reactions became "faster." Is there a relationship between the action potentials on the molecular level, and experience in the psychological or material sense?
Mahvish Qureshi's picture

batteries and action potentials

While at first the analogy of an action potential to a battery, was confusing and a bit of a strange concept for me. I have learnt about action potentials, etc. prevously from other bio classes and have used batteries attached to a voltmeter to measure the voltage between two terminals, I have never thought of the action potential as a battery.

However as Thursday's class progressed I began to understand the connection between a battery and an action potential much more. I think it is amazing how similar the two methods of transferring energy are so similar.

I think that thinking of the nervous system and behavior with these new terms in our vocabulary it is a bit more plausible to explain the phenomenon of an input with out a visible output. If the signal does not generate a strong enough action potential then there will not be a stimulation throughout the nervous system to generate a response/output. Similar to this a battery can die out if the concentration at an annode or cathode becomes to high and inhibits the chemical reactions from happening. If the chemical reaction is inhibited there is no response and if the action potential s not generated strongly there is not out put.

 

Caroline Feldman's picture

In class we discussed how an

In class we discussed how an action potential is related to a battery. I found a site that compared it to an electrical wire “An 'action potential' is the name for an electrical message carried along the axon or dendrite of a neuron, like an electrical impulse carried along a wire. These tiny electrical signals would not be able to travel very far if the axons were not insulated. Once this electrical charge or 'action potential' reaches the synapse, it triggers neurotransmitter release to enable the signal to reach the next neuron in the chain. A wire carries electricity both faster and farther when it is insulated. The longer the wire is, the more important the insulation is for efficient conduction. The same thing is true for axons and action potentials that travel down them. An action potential is triggered within the cell body of the neuron after the neuron receives signals from other neurons”. Then it goes into how fast an action potential can be carried: “The insulation around axons is provided by a protein covering called myelin. In the brain and spinal cord, myelin is made by oligodendrocytes. The myelin wraps around each axon in many layers. Axon fibers insulated by myelin can carry action potentials at a speed of 100 meters per second, while axon fibers without myelin can only carry action potentials at a speed of 1 meter per second”. How does myelin and this insulation process work to increase the speed of an action potential?

http://www.apacure.com/Why-is-Myelin-Important.html
Tara Raju's picture

Battery, Myelin, Etc.

The battery analogy was not one of my favorites- for me, it just left to many questions unanswered. I was looking online and google and I stumbled upon a website (www.mult-sclerosis.org/actionpotential.html) that discusses this topic. It says: "An often used but slightly misleading analogy for how nuerons work is to compare them to electrical wires along which nerve transmissions flow. THis is not actually how they work. A better analogy is to imagine a skipping rope lying on the group. If you take hold of one end of the rope adn give it a quick vertical flick, a wave will move along the rope away from your hand. Nothing except energy actually moves down the rope and, whtn the wave has finished, the rope is in the same position it was before you sent the energy along it". To me, this jump roping analogy is more along the lines of what I imagined the nueron transmission actually occured. I have always thought it was a quick impulse and then the activity returned to its original state- I am not saying that I am not open to new ideas about how it actually works, I have always just thought this was so. For the myelin sheath, I tend to think of this has a wire casing. On thick wires, like our internet cords, the rubber that holds them all together is what I tend to think of the myelin sheath. It holds the impulse together and contains materials that foster the ability to send the impulse quickly and without it, the message could be lost along the way.
Zoe Fuller-Young's picture

Myelin

Caroline's raising the topic of the Myelin Sheath is very interesting to me. The analogy of the battery has mostly confused me, but it is starting to make sense to me. I think that the problem is that when I think of a bettery, I also think of electricity, and an electric pulse. Prof. Grobstein argues that we should not think of action potential in terms of electricity because electricity travels at a much higher speed than a signal through an action potential. However, I still find it helpful to combine the idea of a battery with electricity, as long as we recognize that an action potential is a slower process. This way, I can better imagine how the batteries go from one charge to another, and that activity remains during resting potential, much as electrical power is maintained even if the light bulb is not turned on.

According to this website,   http://www.miracosta.cc.ca.us/home/sfoster/neurons/mylen.htm , it seems that the definition of myelin includes the word electrical. Why is this? Should we assume that it is battery-like and electrical, or, as Prof. Grobstein argues, do not think of action potentials as electrical.

In trying to understand Myelin and speed of signal, it is interesting to look at Multiple Sclerosis, as it is (according to Wikipedia) " a chronic, inflammatory, demyelinating disease that affects the central nervous system ... Symptoms of MS, a demyelinating disease, are changes in sensation (hypoesthesia), muscle weakness, abnormal muscle spasms, or difficulty in moving; difficulties with coordination and balance (ataxia); problems in speech (dysarthria) or swallowing (dysphagia), visual problems (nystagmus, optic neuritis, or diplopia), fatigue and acute or chronic pain syndromes, bladder and bowel difficulties, cognitive impairment, or emotional symptomatology (mainly depression). and also... changes in sensation in the arms, legs or face (33%), complete or partial vision loss (optic neuritis) (16%), weakness (13%), double vision (7%), unsteadiness when walking (5%), and balance problems" -sorry for the long quotation, but I found it interesting that problems with Myelin can cause so many symptoms, and I wonder how understanding Myelin, and Multiple Sclerosis as a disease of the Myelin, can help us understand action potential, and action potential as a battery/electrical pulse, and questions of speed?

 

Anna G.'s picture

Supporting Furthering Action Potential=Batteries

Like Jackie, I found the idea of action potentials being like a battery interesting. While the idea makes sense to me, I don't necessarily understand the need for the analogy, and am looking forward to seeing where this goes.

 

If we accept this analogy, we have to look at what this means in respect to the whole system. If the system is simply a flow “like" an electric circuit, we don't have a way yet to explain how the action potentials are propagated, and how each neuron speaks to the next.

 

I really liked Jackie's "proof" for the battery idea, by discussing the Intro Bio lab. I didn't think about it that way, but it's true. Using a naked nerve cord that was "dead" but physiologically active still, is similar to a battery that you can just remove. This way of utilizing the analogy shows that the signals, arguably one of the lowest levels of work in brain, are nothing more than a mechanical/electrical system.

 

I think that an important thing to remember when were talking about action potentials all being the same is that sensory organs are made up of specialized cells. So that while action potentials may all be the same, the cells that are receiving them take that input and translate them to the i-function in different ways.

 

Jackie Marano's picture

Action Potentials as Mediums

I think Anna brings an excellent addition to the 'furthering of the battery argument' analogy that I made just above. Anna's statement about how all of the action potentials are the same, but that input and output signals are different is quite interesting. Perhaps another battery anology can account for this phenomenon, and also about the switching of various sensory (visual and audio) "boxes" that was mentioned above in the forum:

Every battery contains potential energy that can be transferred into some sort of circuit or system. BUT, if the incorrect type of battery is inserted into a system, nothing will work. Auditory and visual sensations are both recieved and translated from the nervous system via the same medium, action potentials. Similarly, a 9V battery and a AAA battery both put energy into a system using the same form of battery juice medium. So, just like my AAA-battery Texas Instruments graphing calculator will not run on a 9V battery, the auditory and visual sensations will not run/function on each other's action potential in the event of a switch. I'm not sure if this helps with any of the above-mentioned confusions...but I think that the idea of limits existing between multiple methods of communication that function on the same medium is important.

 

Jackie Marano's picture

Furthering Action Potential=Batteries

I found our Thursday discussion about action potentials and batteries to be very interesting. What we discussed on the scientific level complements most of what I learned in Intro Bio, but the approach is certainly different. While we certainly covered concentration gradients and the transfer of a message via electric actions between sodium and potassium ions in Intro Bio, we never related such a critical biological process to the function of a battery. I decided to do some further searching to see if there was additional information about action potentials behaving as batteries, and this is what I found:

Wikipedia: "Cell membranes that contain ion channels can be modeled as RC circuits to better understand the propagation of action potentials in biological membranes. In such a circuit, the resistor represents the membrane's ion channels, while the capacitor models the insulating lipid membrane. Variable resistors are used for voltage-gated ion channels, as their resistance changes with voltage. A fixed resistor represents the potassium leak channels that maintain the membrane's resting potential. The sodium and potassium gradients across the membrane are modeled as voltage sources (batteries)"

I think this further details the relationship between action potentials and batteries, and thus strengthens our argument. Additionally, a major contributor to the validity of our battery model is, in my opinion, the fact that action potentials can still be produced/measured for some amount of time AFTER the system/organism has died. Clear evidence of this is that students in BMC Intro Bio lab collected action potential data from nerve cords completely cut/removed from earthworms (that died after this 'nerve surgery'). Perhaps the best analogy I can think of is that even when the circuit within a flashlight/battery-powered device ceases to work (for reasons other than dead batteries), one can STILL remove the batteries and use their potential energy to power another device!

anonstudent01's picture

Where Signals Go

In class yesterday a distinct image popped into my head while we were discussing auditory and visual signals/ action potentials: A telephone operator controlling a switchboard. If the action potential that propogates when you hear something is the same as when you hear something, does that really means that we potentially could move the extension from the auditory to the visual "box"? And are our Nervous Systems really like switch boards that propogate input manually because the signals aren't created uniquely for specific functions? I really don't like the battery analogy and am interested to see where we go with it.
Caitlin Jeschke's picture

Hearing Lightning, Seeing Thunder

I was a bit confused by this concept as well...I understand the fact that each individual action potential is the same, but I feel like input and output, which are patterns of many action potentials, are a different story.  Eyes and ears receive input in very different ways (sensing light v. vibrations), and so the patterns of input signals that are sent through the nervous system when we "see" lightening are not the same as the patterns that come from "hearing" thunder.  And if one were to somehow "switch" the cables, so as to send visual signals to the auditory box, and auditory signals to the visual box, then I think that the perceived output would be quite different from the kinds of sights and sounds that we are used to...wouldn't they?  Maybe these types of phenomena are similar to what happens to individuals with synesthesia?...although I don't really know enough about that condition to make a connection.  Anyway, just some things to think about.
ptong's picture

Tasting Blue....

Someone once told me that as a college student he/she wanted to try LSD because he/she was told that one could taste blue (apparently she really wanted to taste blue). Anyways, I think hearing lightening and seeing thunder has very similar relationship with tasting blue. I can definetly see how the drug can temporarily switch/play with the brain to cause senses to switch. However, since most of us have never gone down that path (I think), it is hard for us to really understand people who have experienced synesthesia. Just because we haven't experienced it doesnt mean it doesn't exist.
Jessica Krueger's picture

I too...

Would like to see more discussion either here or in class on what Professor Grobstein meant when he introduced the concept of hearing lightening or seeing thunder.

Was he referencing the fact that all our sensory perceptions are translated into the same action potential, which when viewed from "above" would look exactly the same? Is he making a nod towards the brain's central role in the construction of sensation? Why is this different from or how is it related to synesthesia?

As per my post last week, synesthesia may result from higher connectivity between processing centers in the brain (oh diffusion tensor imaging, how cool you are). So in addition to having the pigment in the back of your retina change in the presence of light, which in turn converts to an "eletrical" signal along the soma of the "vision" neuron, which passes along the axon as an action potential through the thalamus to the occipital lobe to be perceived as vision, another errant axon picks up the excitation along the way and in carrying it to the temporal lobe produces the sensation of hearing... I think. Does this view lend credence to the earlier analogy of the production of sensation as a telephone switchboard?

Caitlin Jeschke's picture

Wow!

That is so interesting!  I guess if someone's "switchboard" is organized in such a way that an input signal gets transmitted to more than one major box (i.e. visual and olfactory) at the same time, it would be capable of producing outputs similar to the sensations experienced by those individuals who are synesthetic (like "tasting" a particular color). 

One thing about your answer really stood out to me:  you describe an "errant" axon that somehow picks up a signal from the "normal" pathway, and allows it to continue along two separate cables.  It struck me that, at least in synesthetic individuals, these "errant" pathways are fixed-a particular input always leads to THE SAME abnormal output (for example, the individual will always experience the same taste sensation upon seeing a particular color).  This makes sense in terms of the switchboard model, because the "circuits" have been connected in a particular way in that individual since the nervous system developed. 

That said, some further questions: how then do we explain nervous disorders that seem to indicate, for lack of a better term, "random firing", so that it is impossible to predict the pattern of output that a person will experience?  Also, in class, we touched on the possibility that neuron connections are capable of changing, and that such a change would cause a change in behavior.  Are "random firing" types of disorders caused by changes in neuron connections?  Why is it that some pathways seem to be more prone to change than others (ex: thought pathways are constantly modified, whereas a synesthetic person who sees the letter "A" as red is very unlikely to all of a sudden perceive it as blue)?  I would like to discuss these ideas more in class.

Paul Grobstein's picture

getting started early

Lindsey C had some thoughts/questions before I got this forum up. Will be quicker next week.
randomness