Understanding behavior comes from many avenues, but none of these can be explored until the most fundamental aspects of the human nervous system are studied. It has been established that the nervous system is essentially a bunch of boxes within each other. The notion of autonomy has also been laid out on the table. To take it a step further, the smallest of the boxes, the neuron, is composed of many differnt types of batteries, dependent on membrane concentrations. The different membrane concentrations causes an electric field. These are key ideas that are important to understanding behavior. This is because ultimately these processes are the foundations to the bigger picture. Potentials govern the way sensory, motor, and interneurons operate. They are the reasons inputs and outputs occur leading to the involvement of the neurons. Everything in the nervous system can be described by ion potentials and concentration gradients. Is it then safe to assume that behavior is the result of a bunch of ions passing through membranes at a selected time? I think this idea might be uncomfortable to many people, but they way this information is leading, one can't help but see behavior as basically a chemical process.
Or at least a physico-chemical process. Or, more accurately, an enormously large and complexly interacting set of physico-chemical processes. Maybe less uncomfortable that way? PG
Well, the really obvious answer of "Studying how action potentials are generated is important for understanding behavior, and definitely warrants a serious consideration" is just too pat and saccharine for me to allow myself to write. I think there is a decent case for each side. Spending a week on action potentials may be fine for some, but I like synapses, and what happens there, more than I like neurons and axons and depolarizations and thresholds and permeabilities, etc. Although neurons have thousands of connections to and from each other, action potentials don't communicate at those connections, neurotransmitters do. A neuron can only transmit one action potential, but it can receive input from receptors sensitive to many different NT's, and possibly transmit different NT's (I can never remember whether they can or can't).
The flip side, though, is that to know which NT's to release with what frequency in reponse to which dendtritic receptors, an action potential needs to communicate down its length, and the frequency and firing pattern of these AP's adds another whole dimension to the complexity of nervous system activity. What we learn about potentials is a complement to synapses, an important base, well understood and much observed, that links one synaptic release to another, adding a new level of complexity to the process. While understanding synapses is what interests me, it's impossible to do without knowing what lies in between them.
It isn't actually so saccharine a question. Lots of people argue quite seriously that what is critical for behavior is some set of more abstract information processing rules, and that those can be derived and understood independently of the particular physical substrate in which they are instantiated. In which case, its not only action potentials but synaptic potentials which can safely be ignored. Assuming we don't buy that argument, the action is indeed at the synapses, but what goes on there depends (as I've argued) on exactly the same set of basic phenomena one sees in action potentials. Hence, its all part of the same understanding, no? PG
The topic of neuron signals, how they are created and what is their role in behavior is definetely worth spending a lot of time on. In all the previous biology classes that I had, I was never really told WHAT EXACTLY CREATES AN ACTION P0TENTIAL AND HOW DOES IT MOVE ALONG THE AXON. And that's a shame because understanding these concepts really helps me to understand why one reacts to some things in one way and to others in the other way, and why in other cases one would respond in the same way to the same stimuli. This concept also helps to eliminate the confusion as to what can account for the autonomy of the nervous system, and the topic also helps to uncover some of the "magic" that is hidden behind the concept of behavior.
As it was said in lecture, all of the signals passed from different inputs whether they are visual inputs or oliphactory, or audible, are sent along the conceptually-same pathway: by a chain of neurons. Inside the neurons the signals are transmitted in a form of the membrane permeability changes. How then does the organism distinguish between all the different inputs that are sent to it? I would guess, that the route that the signal came from and the final destination of the signal play a crutial role in this matter. For example, it was mentioned in lecture that there are twelve cranial nerves in the human brain, each of which is responsible for the different functions. Could it be that the signal that was received by one of the nerves (for example, the olfactory nerve) follows a special pathway different from the signals that are received by the others, and by the place where it arrives (i.e. by the way it arrives: special neurotransmitters used at the synapse, special receptors, etc.) an organism is able to distinguish between the different signals. On the other hand, it is probably true that if one would stimulate the "wrong" sensory neurons, the signal that would come will not depend on the input as much as on the neuron it came from. For example, if one person would sit with his arm stretched out in front of him, and somebody else would very slow touch his arm from the wrist to the crook of his arm, there will be two completely different responses dependent on the pathway the signal would come in from. Let's say that the first person watches the movement of the other person's hand. In this case, the person will know exactly the time when the other person's hand reaches the crook of his arm: notice, that the person will know because the signal primarily come from his eyes' neurons. Now, imagine, that the first person turned away, while the other person SLOWLY moves his hand across the first person's arm. Then, being asked to tell, when the other person's hand reaches the inside of the elbow, the person will invariably respond about 2-5cm before the inside of the elbow is reached. This experiment shows that the response to a specific stimulus depends primarily on the route it reaches the person's nervous system as opposed to the stimulus itself.
The membrane permeability changes and the passive flow aslo help to account for the autonomy of the nervous system. Such a theory can explain how some signals can originate without any obvious input into the nervous system. This autonomy could probably be used to help to explain the behaviors that are established by human personality (i.e. creativity, sense of humor, thought process, etc.)
Glad you think it worth the time, and intrigued by your additional thoughts. Yes, as we talked about today, similar action potentials/different experiences because in different neurons. And yes, route can make a difference for experience of one thing (I think I'm understanding your point correctly). Certainly the time the inside of the elbow is touched might appear to be different if based on information from eye as opposed to information in cutaneous nerve (though I don't quite see why a "5 cm" difference). To make the situation even more interesting, under normal circumstances one gets both kinds of reports (optic and cutaneous nerve). And if they separately lead to different sense of when something happened, what happens when they are both there? PG
I was really interested in Wendy Sternberg's monday night supplementary session material. The whole idea that all of this research was only being done with male rats for so many years is incredible to me. I believe there are many obvious differences in the sexes that should be accounted for in a model for pain inhibition. Thinking about it from an evolutionary perspective brings up pleistocene era hunter-gatherer society concepts. This historical model (if I recall correctly), generally differentiates between sexes by the respective roles that each played in the family. The man generally did the hunting for the family, while the women would tend the home dwelling, take care of the kids, and take care of general gathering duties. Now, one has to admit that the amount of stress related to these two roles is enormously divergent. The stress of survival needs seems like it would have a different response than stress of general housekeeping needs, so perhaps stress responses evolved differently in men than they did in women for this reason. One point that was brought up was that of stress of childbirth. I thought this was interesting in that it did bring the scale back in the other direction-women really do experience a more debilitating stressor regularly in childbirth, and thus could develop as strong a response to stress as that of a man who is stressed by the rigors of hunting vicious man-eating animals everyday. The point is, the stress response has evolved differently for different groups according to their experiences, and so it makes sense that the hormone mechanisms underlying the stress response would also evolve differently. Clearly, any models that may involve mechanisms that could be differentiated by sex must be tested for sex differences, or else their validity remains questionable.
Glad you enjoyed it. So did I. And there is indeed a need, in science and elsewhere, to take more seriously the reality that brains ARE all different from one another ... so that conclusions drawn from any restricted sample may or may not be applicable to other individuals. PG
Examining the nature of the generation of action potentials in single cells to better understand behavior implies that abnormal behavior should be associated with abnormalities in the behavior of neurons. In a sense, this approach to studying behavioral neurophysiology views the nervous system as an information superhighway for our bodies. In addition, all behavior, both internal (unobservable) and external can be conceptualized as forms of communication both within our bodies from one structure to the next and between ourselves and our external environment. At the basis of these communications is the neuron. The observable/measurable behavior of the neuron takes the form of the action potential. Disruptions in the behavior of neurons can take a number of forms, but essentially in each case, there is a disruption in the communication of one neuron to the approximately 1000 neurons onto which it projects. The ultimate expression of that neuron/the end product of its action potential is the release of neurochemicals into the synaptic cleft. Therefore, a disruption in the generation of potentials should be expressed in altered levels of neurotransmitters being released. This disruption in communication amongst neurons should correlate with disruptions in a person's overt behaviors.
One example of a breakdown in affective and cognitive behavior that is associated with altered levels of neurochemicals is schizophrenia. Studies of schizophrenics have found a correlation between the negative symptoms of schizophrenia and a decrease in metabolic activity and a decrease > in dopaminergic activity in the prefrontal cortex, a condition referred to as > hypofrontality. Axons from cell bodies in the VTA comprise the MFB, and their terminal endings project onto the prefrontal cortex. One of the structures with which these dopaminergic endings synapse is the nucleus acumbens, a mediator of attention and reward mechanisms. In people not suffering from schizophrenia, the EPSPs from glutaminergic neurons, which synapse with the the dopaminergic neurons at the nucleus acumbens, ensure what is referred to as a tonic release of dopamine. However, in schizophrenics there is a decrease in activity of glutaminergic excitatory input to the dopaminergic neurons resulting (characterized as phasic rather than as tonic) in an subsequent decrease in the release of dopamine to the synaptic gap at the NA. This decrease in mesolimbic dopaminergic activity is associated with the negative symptoms of schizophrenia. Conversely, one hypothesis to explain the positive symptoms of schizophrenia is that due to the decreased dopaminergic activity at the synapse, the DA receptors in the nucleus acumbens actually become more sensitive.
Numerous other examples of how behavioral dysfunction correlates with neural communication gone awry -- Parkinson's disease, the frozen addicts, and even sociopathology to name a few -- exist. What these examples imply is that by examining abnormalities in the outputs of individual neurons, the biological source of the disruption in behavior can be found. In other words, altered single unit activity can communicate to a doctor the possible disruption of specific structures, > regulatory mechanisms, or even the generation of potentials themselves.
Nice and important examples of the material basis of behavior. Interestingly, it comes from a tradition, neuropharmacology, which doesn't strictly depend on knowing how action potentials work ... and in fact didn't pay much attention to that for a long period of time (perhaps appropriately). We'll talk a little about the relation between the two traditions in the next lecture, as it happens. PG
The differences between the mind and brain is an intriguing distinction.> There is important because each part seems almost to embody a different set of functions we seem to embody the physical parts of being into the brain, wherein are regulated breathing, heartbeat, regulation of hormones, all things that our body subconsciously does for us. The so called "conscious" functions, are in our mind. The author/neurobiologist Damasio seems to be trying to find a reason for being - the reasons for how we behave and an explanation for our actions. In his portrayal there is the unknown factor, the search for understanding of the ever fluctuating mind. His "mind" is most definitely determined by reason and emotion, emotions are scientifically explained as the basis for reasoning. His depiction contains a certain dualism - the world as we see it and the world as we interpret it. Reasons and emotion are one of the most influential factors in our behaviour. Reasoning, long believed to be the calm, cold logical part of the brain, does in fact need emotions to temper reactions. Damasio states an interesting case in explaining that emotive sensation is one of the most vital inputs into our world view. We need emotions to help evaluate a case, emotions call to mind everything that is linked to a certain situation. Reasoning helps us to analyse and deal with a situation, but as in all things it must be tempered by emotion. Behaviour is a reflection of this duality, we must have both in order to be able to interact socially with the rest of the world. Man cannot live be reasoning nor emotions alone. The wholly reasonable man, is lacking a very serious part of his world, he cannot respond with emotion, thus he has no measurement against which to judge. The same way that a wholly emotive person cannot survive. Emotion is very flighty capable of drastic, variable changes without rhyme or reason. This is where the action potential becomes very important, because these two parts of the mind seem to be interlinked according to the research of Damasio, the neurons are capable of self stimulus, and thus reasoning through completely imaginary situations or feeling emotion at figments of the imagination. Because action potential can be self starting there is always the possibility of imagination, and thus we are better prepared to deal with unknown situations when they face us. Thus emotion, reasoning, and action potential are a way of protecting us from future dangers. We prepare ourselves, emotion can cause reactions in the body which signal warning colors, such as a blush. The action potential translates an emotive pathway into a physical expression.
Reasoning is mostly contained in the mind. It is a very important part of our behaviour interaction, because it is usually a response to exterior inputs or else interior thoughts. These have caused us to cogitate - the neural circuitry is set into action causing other parts of the brain and body to function, either protecting us or causing further trouble. Behaviour can sometimes be seriously affected by emotion, it seems that sometimes emotions are the over ride "button". Emotions will cause us to act in a certain way regardless of the opposing reasons against something which may be foolish. This seems to be the body's way of reacting to certain seemingly important stimuli, regardless of how the "higher" sense may feel. Emotion, reasoning, and the action potential are an integral and vital part of behaviour.
Intriguing, provocative linking of several sets of readings (know there is a multiple book review of Damasio on Serendip, done by an earlier class? at http://serendipstudio.org/bb/damasio/descartes.html). Very interesting thought, that one can see the action potential as the intermediary between the emotive and the physical. Too pursue the thing a bit further, though: presumably emotion and reasoning are themselves simply patterns of action potentials, no? So action potential not so much a bridge between emotive and physical but the ingredient out of which the emotive (as well as the rational) is made? PG
Understanding how potentials are generated in a cell, as was said in class, will allow us to understand how the brain differentiates between fear and happiness or lightning from thunder. It is quite amazing that the brain is composed of neurons that can differentiate into diffrent jobs and learn how to differentiate between different inputs. >From understanding potentials, perhaps we can learn whether an imbalance the gradient or concentration can lead to erratic behavior or diseases. And with this knowledge, we can also ask how much of our behavior are we responsible for. If action potentials can be generated by itself, is there something beyond the "box" or something within the "box" that is controlling these action potentials. Other implications of learning about action potentials may be understanding how the environment may influence the concentration gradient or the nature of the action potential itself. Can we manipulate the membrance concentration, permeability of the membrane or the current flow to alter behavior?It seems that since that potentials is the language of the brain, it is crucial to decipher it and understand the meaning of it.
That's a LOT to ask for, but understanding potentials will (I hope) at least give us a beginning. They won't, though, show us how brain distinguishes lightning from thunder. Instead, they will help us to sharpen that question by showing us what does NOT distinguish the two (the potentials are the same), and hence force us to look in a new direction (how potentials are interpreted in larger groups of neurons). That same point will apply for some of the other things you mention. PG
Is understanding the "boxes" in "boxes" and the "boxes" different potentials > worth spending a week on?
Yes. Those potentials are what makes the movement of information travel from > the source of the input to the output. Or as discussed this week, these potentials explain that there is no need for inputs. That the nervous system is controlled by semi-permeable membranes,electric fields and concentration gradients. This is very important to the understanding of behavior. Relating this back to the person with a broken neck however now confuses me.The information travels down the axon so how does this information flow become "broken"? I understand the information can not get from one place to another,but the axons are still there. Are they crushed? and how can they be "crushed".
The entire conversation of potentials is very important, it stresses the notion that the process is "highly improbable". Yet, the reactions of this system cause the moving of information. What remains to be answered is once the information gets to the destination, how does it then cause an output? If > an output is the result of the flow of information.
Crushed or, more likely, totally cut. Hence the information can't get from one place to another. And causes output by synapes, chemicals released which act on muscle (yes, by altering permeability, as we'll see) PG
I believe that it is worth spending a week discussing action potential. Although it may not have shed and immense amount of light on the question of behavior, it was indeed a large step in understsanding behavior. Armed with the knowledge of how the brain relays its messages and the energy transfer involved, we begin to understand why the body reacts to certain stimuli.
As always, with the aquirement of knowledge, new questions will arise. Why have the circumstances responsible for the maintenance of action potential evolved the way they have? Can there be repair of damaged neurons which are no longer capable of relaying action potential?
As we begin to understand more about the processes in which the nervous system relays its messages, we will begin to ask more probing questions. Hopefully coming up with some interesting answers and some new questions to be answered.
What's the difference between "shedding light on" and "understanding"? Its an interesting distinction: one is getting ready for something and the other is doing it? Hope (too) you get some of the latter as well. And yes, can usually tell if new and interesting questions come up. PG
According to our theory, the brain is a series of connected little boxes. We have now learned that these boxes are neurons, and specificly, we have learned that these neurons functiuon by using concentration gradients to send an electrical charge. The gradients are complex and how they work needs to be throughly understood in order to understand brain function. Spending a week on them is definitly worth it. Trying to understand the brain without understanding neurons would be like trying to do calculus without being able to add. Now that we can understand how these neurons work, we can begin to look at how they work and interact together and how this relates to behavior.
All of the studies done on grashoppers, crickets and cats have been looking at which neurons fire when, and how these stimulations relate to movement. These animals are what have been studied the most becuase simpler animals have less neurons and are more easy to understand. Additionally, movement is much more easy to study than thought. But interesting studies have been done on brain function in humans. PET scans were done on two sets of people. Those who tested high on standardized test an those who didn't. The test were done while the people were taking the exams and it was found that people who had high scores had specific pathways in the brain that light up when answering a question. People who scored low used their entire brain, and if they did use a pathway, they used a completely different pathway from the other people. So behavior can be related to the pathways that the neurons use, and now that we understand how each individual neuron works, we should better be able to understand these pathways.
Good argument, and good extension. Yes, seeing how single cells participate in easily visible behaviors, like movement, pave the way for making sense of the relation between broader patterns of neuronal activity and less easily observed behaviors, like thinking. And, in both cases, knowing the underlying physiology is important in properly interpreting the observations. PET scans give a good overall picture, but not a fine-grain enough picture to know whether people are or are not using SOME "pathway". It may simply be more obvious in some cases than others (because activity is grossly more localized). PG
Last week I wrote about the awesomeness of the neuvous system in its ability to generate such a diverse set of behavior as that of human behavior. It seemed amazing to me that the only reason I can type this message is that there are some unfathomable number of neurons firing in a specific frequency. I will never repeat these same motions in the same order > again.
And now, what continues to fascinate me are the processes that allow for the neurons to fire as they do, in addition to those that allow the neurons to fire at all. For instance, embedded in the membrane of a typical neuron are "perhaps a million sodium pumps with a capacity to move about 200 million sodium ions per second" (The Neuron; 5). The membrane proteins that constitute these million sodium-potassium pumps change configuration for each transferral of ions. The sophistication of these membrane proteins, as seen in their involvement in transporting ions across a membrane and thus generating the concentration gradient crucial to the generation of action potentials, allows for the creation of human behavior.
It seems odd that particles of such minute size could be at least partly responsible for human history--for the construction of the Egyptian pyramids, for the existence of the computer, for the development of the electron micropscope. Great things are necessary a result of innumerable small, seemingly unimportant events.
Nice thought. Maybe there's an important general lesson in that, huh? PG
The mechanism of the Action Potential sounds very reasonable and rational enough. However, it is difficult to comprehend exactly how does a sequence of action potentials actually translates into such complicated processes as feelings, thoughts, decisions, beliefs, movements etc...
Yes, we can claim to understand the core mechanism of the action potentials and, therefore, the nervous impulse, but how can it be all that is behind "us"? It is difficult to think of us in terms of just ÔcomputerÕ programs in which the existence of the concentration gradients in the environment of a specific axon is all that is responsible for the incredibly broad range of the possible behaviors. I do understand that we possess a great number of greatly different neurons so there are a lot of possible combinations of possible concentration gradients. Yet, are there really enough possibilities to result in so many various behaviors? It seems to me that there is an infinite number of behaviors but there is a finite (a very large, but yet, finite) number of the possible combinations of concentration gradients and their possible locations. So how can there be a relationship between these?
The complexity of the "program" that translates an infinite number of inputs into a finite number of possible concentration gradients, which it then translates into an infinite number of outputs is just incredible. And it does not even run out of memory. Or does it? Maybe we forget things because the "computer" decided that we donÕt need that specific memory anymore and translated something more important over it. Will we ever know?
An interesting way to think of it. Perhaps, though, you're using too much of a computer metaphor. There isn't so much a program which translates inputs into gradients, as a set of gradients and permeabilities which is both the translator and its product. Similarly, there isn't so much a distinct program and memory as a single thing which serves the functions of both. A finite number of states (possible gradients and combinations)? Hmmm. Not sure. That one I have to think about more. PG
It seems reasonable to have spent a week talking about potentials since that is how the nervous system conducts inputs, outputs and all signals among neurons. An action potential is what induces the body and the brain to carry out a behavior, whatever it may be. Looking at this in a very simplistic way it seems to me that since potentials are how neurons communicate, that potentials ARE behavior.
However, seeing potentials in this light raises many questions. For example, how does the brain and the whole nervous system differentiate between potentials? How does the brain distinguish between an action potential caused by music and thunder? Furthermore, how are potentials translated into thoughts, emotions, etc. How can the simple change in membrane permeability, concentration gradient and electrical field of the axon (along with the synapse) be responsible for the communication between the neurons, which in turn is responsible for all the functions in the brain? I am awestruck at how the movement of ions across a membrane can yield the wonderful and complex functions of the brain.
I am also very intrigued at how the having a section of a membrane permeable to Na+ next to a section permeable to K+ leads to spontaneous actions potentials which makes neurons semi-autonomous. It is amazing that such a basic mechanism is what allows the heart to beat outside the body, and what allows me to create thoughts of my own.
The more we study the workings the brain and the nervous system, the more I am amazed at the evolution of man and "intelligence".
Pretty amazing indeed (though maybe inevitable?). And yes, new questions, some of which we've begun to answer (thunder vs lightening, a distinction in where action potentials occur in an organized network of boxes). And some answers hinted at: isn't so much a potential that is a thought but a pattern of potentials across lots of neurons (presumably). PG
Was it worth an entire week of class to reach a better understanding of how potential is generated in a single cell? In my eyes, by all means, ofcourse it was. Why does Bryn Mawr makke every freshwomen take a liberal studies english class their first semester? In my eyes, it is essential foe everyone in such a class grouping to start off on a generally, similar first step. Only is the very basics are agreed upon and recognized can a class begin to build arguments and more in depth theories. And besidees, I'd hate to think that all those weekly liberal studies I turned in as a freshwoman were worthless. :)
I also think it halps to have recognized on such a small cellular, iceroscopic level because, often it is difficult to relate something so macroscopic as physical behavior to something within the human nervous system, so minute. Understanding the signaling process due to close proximity which neurons display lends a helping perspective on just how electric and quick reactions within the human nervous system take place.
The downfall however of spending so much time on the actual speecific mechanism of behavior takes away from it's mysterious qualities. I aam one who likes to think that each person in the world is unique, appreciate it, and not ask into too much depth...why.
But maybe looking in depth turns out to enhance the sense of uniqueness, and the appreciation of that? Common first steps are useful, particularly if they lead on to an understanding that similar first steps necessarily point on to uniqueness? PG
In terms of understanding something more about behavior through studying potentials generated in cells, i believe there is merit in this statement. Understanding action potentials helps us to understand how behaviors come about. This technical process of ions flowing in and out of the membrane in order to balance the concentrations, etc. is all the result of a input. This input can be received internally, such as with a headache, or it can be received externally, such as with touching a hot stove. These inputs warrant outputs, and the process of how the reaction occurs is extremely important.
Once this detailed description of where outputs come from is understood, artificially induced changes in the system may possibly be applied in hopes of inducing different behaviors as well. That is, action potentials seem to place large focus on concentration gradients of the ions, and understanding this may help us to be able to change these gradients. Since the gradient change is what causes potentials to change which in turn cause behavior to occur, artificially induced gradient change may produce different behaviors. This may be very useful in aiding in depression or hysteria.
Interesting, and will indeed be able to learn more by artificial perturbations of normal processes. Be careful though. Its not actually the gradient (at least not the concentration gradient) that changes to account for action potentials and the like. The concentration gradients remain the same, its the permeabilities that change. PG
Knowledge is always worth the time spent learning it. However, apart from the intellectual satisfaction gained from learning about action potential and their transmission mechanisms, is it really worth spending so much time on action potentials in trying to understand the implications for the larger functioning of the nervous system?
There's always the danger of losing sight of the forest for the trees, as the saying goes. I feel that it is worth the time spent, as long as we are able to relate that new knowledge to the larger picture of the nervous system as a whole; as long as we are able to integrate the two together into an image that corresponds to experimental observations.
Additionally, even though we can conclusively describe the action potential in great detail, and potentially map out all the pathways that action potentials can take, would it really help in understanding the overall phenomena that are the results of such pathways, or would such knowledge eventually prove to be a hindrance to further understanding?
Using an analogy from physics, we think we understand the more complex atoms in a quantum mechanical probabilistic sense, but we cannot (yet) perform the descriptive mathematics beyond the hydrogen atom, for it is too complicated even for comntemporary computer technology. Similarly, we may be able to completely understand what drives the functioning of the neuron as an independent, autonomous unit, but when we get to the higher or more complex levels of understanding behaviour, perhaps the action potential and synaptic pathway model alone is inadequate.
In the same line of thought, it seems highly reductionistic to claim that the action potential (and all the interrelated potentials, gradients and structures that are implicitly involved in the generation, maintainence and transmission of the action potential) is all there is to the functioning of the nervous system and hence to behaviour. It would make the explanantory model required much simpler, admittedly, but do we know enough about the nervous system at this time to discard the possibility of the role of additional unknown factors?
We do know that action potentials throughout the body can be described using a single model. The question then arises of how different individuals perceive the same inputs in different ways, and often have different outputs? One possible answer may be that their nervous systems are wired differently and although the mechanisms of action potential generation and transmission may be the same in both individuals, the different pathways that those action potentials take accounts for the varied outputs that the nervous systems produce. But then HOW is the different circuitry produced, and why is it different, when both outputs (responses) may have the same desired effect? Why do different people, for example, have different pain thresholds, when a single withdrawal away from the causal mechanism would serve the organism just as well as a withdrawal accompanied by a verbal exclamation?
Interesting and appropriate generalities (forest or trees), AND specifics. Yes, DOES matter that all neurons basically the same in internal processing since that means there MUST be at least one additional important level of complexity (the wiring diagram). But yes, should also bear in mind that there are additional unknown factors operating at the lower level of organization. And next question also appropriate: if the wiring diagram critical (it is), how does IT get put together and why differently in different people (or differently at different times in the same person?). We'll talk a bit about the developmental problem, though its actually a whole course in its own right. AND about why it might vary, person to person, and within a given person. But we'll spend more time on the multiple important levels of organization (the boxes within boxes within ...) that one needs to make sense of the forest as it is at any given time. PG
The first and most obvious answer to the question of whether or not it is worthwhile to spend a week studying how potentials are generated in single cells is that it must be or else we would not do it. However, I am certain that there is a greater depth to the question than such a simple and trite response. The transmission of signals, whether from an external input to a sensory neuron or between axons of interneurons, is the most essential aspect of the nervous system; it defines it as a system and maintains its worth and presence within the body. The single-celled components of the system, the neurons, are the most basic aspect and they therefore are models for the nervous system as a whole. The transmissions and signals used by the neurons are representative of the signals used on a larger scale. It is then inherently appropriate that the nervous system be first understood at its least complex level and such understanding will implement comprehension of the remainder of the system.
To understand behavior, one must return to the statement asserted at the opening of the class: the brain is behavior; the nervous system does not simply direct or control behavior, it is behavior. Having faith that such a statement is true, one can transitively understand that behavior is essentially a series of inputs and outputs. Therefore, it is conceivable that a complete understanding of the process of inputs and outputs in relation to the neurons implies further comprehension of behavior. It is essential in understanding both the nervous system as a physical entity and behavior as a more abstract consequence of it that one gain full comprehension of its most simple element and its functions, namely the potentials of the neurons.
"... it must be or we wouldn't do it" presumes a very large amount of confidence in the instructor. I hope I can live up to that. But indeed some less trust-dependent reasons. Neurons as models of the nervous system as a whole an interesting (and I think appropriate) approach. Am less sure that it is obvious (or even the case) that "a complete understanding of ... neurons" necessarily implies "a further comprehension of behavior". There's a lot of distance between the former and the latter, and it MIGHT be that the properties of neurons are more or less irrelevant. PG
Since the start of this class, actually before it, I have been willing to accept that the brain is behavior. While I still accept that and am comfortable with it, it's difficult to explain many things that go on with behavior, and the more I think about it, the more come up. With the example of the cricket who orients toward the male song, but not on evey trial, although the input to the cricket is the same (the controlled, external, laboratory input anyway) the response is not. Is this response, or lack of it, dependent on several neurons which influence the firing of a couple neurons that determine the pathway that the input will take, or is there something about one neuron that causes it to fire a certain way, with no real predictability or reason? IF that is the case, is behavior random? It can't be, can it? And why would psychoanalysis and therapy prove helpful in modifying many types of behavior. Does frequency encourage one pathway to be activated more than another, so that practice makes (near) perfect? We can say that generally, the femal cricket does respond to the male song, but not always. So can people say that they generally behave one way in a situation? Does saying and believing that influence behavior the next time that situation arises? In some cases, certainly imagining yourself acting a certain way can influence your behavior, but does in a case where someone surprises you, can spontaneous behavior be influenced by which pathway is activated most often. See, that is part of where I get confused. If much of the way that input is processed depends on our genes and on how neurons are connected, etc.how much control can the I function have. I want to say a lot but I'm not sure. And what does it mean when people say that they don't understand why they behaved a certain way. This is something that has definately happened to me. I know that the language center is in one part of the brain, so maybe other parts do know why I behaved a certain way, but aren't able to say it. I have read about split brain patients who, right after surgery, can reach into their closet for a dress with their right hand, while their left hand, much to their reported distress, reaches for a blue one instead. How come the I function gets to say, "I didn't want the blue dress?" What if the blue dress is actually a better choice? Some part of the brain wanted it (If we can use the word want in this situation) So then does the I function have more input into the other input boxes?
I'm sorry that this is a paragraph of questions, but they are things I struggle with in this topic.
Oh, one other thing is thinking. Thinking often depends on input that is already inside the brain, in fact, for me it's eiser to think without having other stuff going on around me. Thinking about a person or situation is one of the things that changes depending on mood or many other things. There again, the same input can lead to different responses.
Don't apologize. Lots of questions, and associated thoughts, is exactly what you should be having. And they are interesting ones, that we'll pursue further. And your general tack is very much along the direction I think we'll be going: there are lots of parts (boxes) without any one always being in charge. And the thing has to be influenced by genes and experience and (in some sense) by oneself. We'll see if we can imagine all that in terms of neurons. PG
I believe that it is worth spending one week to understand how cell potentials operate because they are key mechanisms in a neuron's standard function. We attempt to gain a better understanding of human behavior in this class, but we cannot do so without fully studying the "physical units" of behavior: the neurons. Until we understand exactly how and why neurons function as they do, we will never be able to understand how the nervous system transmits messages via neurons throughout the body, creating the types of behavior we are attempting to study. Cell potentials offer the best explanation for this neural transmission, and as they can be a rather tricky subject to study, they warrant a week of classtime.
Fair enough. Besides which, they help define the next questions. PG
I believe that it really was worth spending an entire week on action potentials. Action potentials are the basis of the entire nervous system. If you don't understand the way in which action potentials work, then you won't be able to understand the nervous system. Learning about action potentials has helped me to better comprehend how behaviors are carried out. Action potentials explain how information can be carried throught the body without using matter. I like the idea that information travels as a wave. It seems to make sense when you think of the nervous system and its many somas and axons. Understanding action potentials helped me to be able to picture the journey of information through the body.
Action potentials also show how the nervous system isn't totally perfect. Because action potentials take time to travel thourought the body, there can sometimes be a significant delay between the time of the input and the time of the output. Therefore, it makes sense that not all behaviors happen quickly enough and why people are clumsy. (i think that the time for the action potential to take effect in my nervous system must be very delayed. maybe that is why i always run into things. it's not that i myself am clumbsy, but it is that my nervous system functions to slowly. although this is probably not true, because in humans, even the longest axons are probably short enough that there couldn't be enough of a delay time that would greatly affect our behavior. oh, well, i tried to find an excuse.)
another thing i don't understand, but that i know we will be discussing this week is how different messages can be sent when all action potentials are the same throught the nervous system. what could possibly be different about the action potential that would allow more than message to travel through when the same type of mechanism is used all the time? is it maybe where the action potential is located? or could it be where the information originally came from? i'm very interested to find out how this can happen.
Appropriate thoughts/concerns. We did take on how can all action potentials be the same question. You satisfied? And yes, is actually true that nervous system activity takes time, measurable amounts of time (partly because of finite velocity of action potentials). And that MAY account for at least some limitations of particular nervous systems (we'll talk more about this). PG
A week devoted to learning about different potentials within ourselves seemed to inform me of new knowledge about behavior. Action potentials seem to be the core of expressing behavior. This moving constant voltage and longitudinal battery (having also autonomous properties) allows our bodies to> generate reactions. These reactions originate from the different chemicals, electrical potentials, concentration gradients and random movement within the> membrane. The membrane is important in this whole process as a boundary layer which separates contents into two different areas. This allows for the movement of such chemicals and electrical charges in and out of the membrane according to the electrical charge and the concentration gradient. Thereafter> an equilibrium is established.
The components which interact with the membrane are of basic elements and processes which seem to be similar to the basic elements of early earth which gave rise to living organisms. The electric field which exists in the membrane existed also on earth where electricity was generated by lightning and thunder creating electric discharge. The random motion of chemicals allowed for the creation of the first basic cells on earth and within our membranes this random motion helps generates reactions to form an equilibrium.> Water is a basic component essential for both conditions. These similarities seem to point to the thought that maybe all matter comes from one source and that everything inorganic or organic evolved from this source of chemicals, random motion, and electrical discharge.
It is interesting to know that a moving wave of permeability changes allows for the flow of information through membranes resulting for certain expression of behavior. These acting potentials within our membranes seem to be the starting point for understanding behavior. It is the smallest part of> the whole box (nervous system). However, if all of us have similar properties> regarding different potentials and information flow, how come we have different behavior among individuals? Individuals of similar backgrounds and> culture express different personalities so what differentiates each individual's behavior?
Very interesting set of thoughts/questions. It is indeed intriguing to recognize things one encounters again and again across all of biology, and wonder whether there is some important meaning in that. And why people are so different from one another, given things which are the same, is a very productive way to approach matters. As we talked about, if differences aren't apparent at one level of organization, it must be that there are important higher levels of organization. Differences due to different connection patterns among neurons, for example. PG
Yes, it is worth spending a week understanding potentials in the nervous system. These potentials are what make up behavior. Everything that we categorized as behavior a few weeks ago such as thought, talking, seeing, etc. are merely potentials in a variety of nerves that eventually stimulate one or more parts of the brain. It is not the potentials themselves that are different from neuron to neuron but it is the frequency at which they are fired that carries the information to a specific part of the brain for interpretation and response. Since there are resting potentials, synaptic potentials, and receptor potentials in addition to a propagated action potential, autonomous behaviors can also be accounted for. Thus, studying potentials in the nervous system is key to understanding how behaviors originate.
Fair enough. Or, at least, the same way I think about it. Usually. Because I can't sometimes help wondering whether there could be a behaving system based on something entirely different from potentials. Possible? PG
Over the normal sunday night dinner and ice cream bar, I was discussing with my friend whether learning about the microscopic events (such as an action potential) is essential for learning about the whole. She was quick to reply that the whole is much more important and hence, we should study the whole and spend less time on the smaller pieces. I thought about that and I made an analogy to that of working with a puzzle. It is true that the finished product, the whole puzzle, is the goal, but in order to reach that, you must examine, shuffle, and fit in place the small pieces. Eventually, everything falls in place, and a clear picture emerges. This is similar to behavior; we have to understand what happens at every neuron in order to string the neurons together which in turn creates a pathway for behaviors to be communicated and understood. So....the answer to whether it is worth spending a week on action potential is a big Yes for me. Although it is hard to grasp the concepts because they are occuring so frequently and on a level that the human eye cannot see, it is these action potentials that are the reason we have movement, thought, etc. You simply can't learn about one without understanding the other. If I follow this reasoning then, because we have no clear answers to behavior, we still have issues with action potentials and small events that have to be dealt with before behavior can be more clearly explained.
I waslooking at the class's essays from last week and, after reading Erin Brown's about the paralyzed friend who had cut himself before the race and wasn't aware of it, I started questioning just how action potentials occur. If there is no leg movement, that can't mean that there are no action potentials, can it? Does this mean there are only resting potentials in the affected limbs and, since there is no movement, there are no action potentials? (now I am REALLY confused). Is it possible that there are different types of action potentials that cause different types of behavior (just a thought)? For example, one action potential causes movement whereas another action potential causes feeling, etc.--I'm not sure if this makes any sense. Also, while in a biopsych tutorial, we were discussing biofeedback, and that makes me curious about how action potentials are affected by such practices as Chi. If we can control certain behaviors, then we must be able to control the smaller steps that make up behaviors.....so does this mean that we can control our action potentials?
Regardless of all my questions, I do believe that any class that plans to investigate and possibly understand behavior must spend time learning the cellular steps--without these, the behaviors will never exist.
Very interesting/thoughtful, thanks. The parts versus whole issue indeed turns up in lots of contexts ... and has, I think, a general answer as you've give it. Properties of parts may (or may not) be directly responsible for properties of whole, but are, at a minimum, necessary to understand what properties of whole are conceivable (since they must derive from properties of parts). And, in this case, some more immediate significances to properties of neurons. No, there AREN'T different action potentials for different behaviors. They're all the SAME action potentials. So how can there be different behaviors? Or movements sometimes, not others? Good question. What it must (and does) imply is that not only the properties of the neurons (action potentials) but also how the neurons are organized and interact is a key factor in behavior. As we'll talk about. PG
It seems reasonable to have spent a week talking about potentials since that is how the nervous system conducts inputs, outputs and all signals among neurons. An action potential is what induces the body and the brain to carry out a behavior, whatever it may be. Looking at this in a very simplistic way it seems to me that since potentials are how neurons communicate, that potentials ARE behavior.
However, seeing potentials in this light raises many questions. For example, how does the brain and the whole nervous system differentiate between potentials? How does the brain distinguish between an action potential caused by music and thunder? Furthermore, how are potentials translated into thoughts, emotions, etc. How can the simple change in membrane permeability, concentration gradient and electrical field of the axon (along with the synapse) be responsible for the communication between the neurons, which in turn is responsible for all the functions in the brain? I am awestruck at how the movement of ions across a membrane can yield the wonderful and complex functions of the brain.
I am also very intrigued at how the having a section of a membrane permeable to Na+ next to a section permeable to K+ leads to spontaneous actions potentials which makes neurons semi-autonomous. It is amazing that such a basic mechanism is what allows the heart to beat outside the body, and what allows me to create thoughts of my own.
The more we study the workings the brain and the nervous system, the more I am amazed at the evolution of man and "intelligence".
Pretty amazing indeed (though maybe inevitable?). And yes, new questions, some of which we've begun to answer (thunder vs lightening, a distinction in where action potentials occur in an organized network of boxes). And some answers hinted at: isn't so much a potential that is a thought but a pattern of potentials across lots of neurons (presumably). PG
Since we have already concluded that brain is behavior, we need to understand how the brain works to generate behaviors. It is worth spending so much time understanding potentials because they are the source of our behavior. I find it intriguing that we know so much on such a very small scale. We can better understand behavior if we study such small details.
Even by knowing about these small boxes, there still seems to be a lot that we do not know, or that we have not yet touched upon in class. One neuron needs input from another neuron to have an output. And for a particular sensational input, there needs to be thousands of intermediate inputs and outputs for a sensational output to result. How can there be so much order, yet at the same so much variability to the nervous system? Changing permeablities.... thunder and lightning.... there is so much precision. I think that it was you who said that the internet is like a complex brain. But I am not so sure that anything can be more complex than the brain. Nothing artificial at least. It would be amazing if we could create something that has the ability to learn for itself over time. And display autonomy as well. Only by understanding every little piece of the brain, every little box, can we eventually lead to a better understanding of behavior. Who knows, maybe then we can create behaviors in other ways than we are used to...
Indeed, there is a LOT we don't yet know/understand. Which is to say that we need to know (as you say) not only how the smallest boxes work but how they are interconnected and talk to one another. "Order AND variability ..." An interesting (and quite general) problem (evolution, the immune system, society?). Am not sure best approach is "understanding every little piece of the brain". Are too many, and run into not seeing forest for trees problem? But yes, maybe create (or at least influence) behaviors in new ways. PG
Is it worth spending a week understanding action potentials and what does that imply for understanding behavior?
For the first time this semester, I felt like the material that we learned in class began to explain some of the biological reasons for certain behavior. But it is not that that I found valuable this week. The lecture regarding the action potential tied in well with the reading on the neuron from last week. The idea that it is electric currents travelling along the myelin sheaths of the axon that communicates from neuron to neuron and from sensory neurons to motor neurons help to explain how muscles and the nervous system inter act.
It also shows how the interactions between neurons are quite deliberate and while the information sent to the brain is the same, still some people react differently to different inputs. And even the same people react differently to the same input. Understanding the action potential provides one side (or rather a portion of one side) of behavior: The biological and chemical interactions that communicate within the body.
The mind and the spirit and the Inner Light also provide part of the solution to behavior, but underlying it all needs to be a tangible process that provides the basis for understanding. Without the understanding of different chemical relationships and electronic transmissions, the class would be scattered. Evryone "believes" different things about what controls behavior--that's terrific. However, in order to have any dialogue on the issue, there must be basic fundamentals that we all agree on and understand. For me, it was the beginning of the understanding of the electric current that moves along the axons running from the tip of the finger to the spinal cord. Eventually, I assume that our knowledge base will grow to see the communication between the spinal cord and the other lobes of the brain and we will have even more concrete material to base our discussions on, rather than a philosophical debate on the mind versus the brain which is ambiguous and difficult to debate.
Nice point. Indeed having something tangible agreed on gives a good base for more productive dialogue on what "controls behavior". And the behavior of neurons potentially gives us that (be careful, though; its not the "currents travelling along sheaths" that communicates from neuron to neuron or muscle but, as talked about yesterday, an intermediate chemical transmission step). We'll keep using that throughout the course to see what collective sense we can make of the differing perspectives that everyone does indeed have. PG
In terms of understanding something more about behavior through studying potentials generated in cells, i believe there is merit in this statement. Understanding action potentials helps us to understand how behaviors come about. This technical process of ions flowing in and out of the membrane in order to balance the concentrations, etc. is all the result of a input. This input can be received internally, such as with a headache, or it can be received externally, such as with touching a hot stove. These inputs warrant outputs, and the process of how the reaction occurs is extremely important.
Once this detailed description of where outputs come from is understood, artificially induced changes in the system may possibly be applied in hopes of inducing different behaviors as well. That is, action potentials seem to place large focus on concentration gradients of the ions, and understanding this may help us to be able to change these gradients. Since the gradient change is what causes potentials to change which in turn cause behavior to occur, artificially induced gradient change may produce different behaviors. This may be very useful in aiding in depression or hysteria.
Interesting, and will indeed be able to learn more by artificial perturbations of normal processes. Be careful though. Its not actually the gradient (at least not the concentration gradient) that changes to account for action potentials and the like. The concentration gradients remain the same, its the permeabilities that change. PG
I could never question that fact that it is very important to spend time to fully understand action potentials. If the neuron is the building block of the nervous system then we need to know all about it (especially its communication mechanism) in order to understand the nervous system.
The most fascinating point brought up so far has to do with how fundamental the mechanisms of the neuron are. I am extremely interested by the thought that autonomy begins at the cellular level, though on an intellectual basis this is only logical. Where else would something begin than at jumping off point of the nervous system? But at the same time how does the cell "choose" to fire? Is it a random occurrence that later on appears as a choice or is it stimulated by some intracellular instance or is there another explanation? Of course this brings up more questions because if we knew how autonomy worked then we could understand behavior on a grand scale from minute behavrios to larger trends in behaviors. Then this would bring into play controls over behavior and so on. If autonomy turned out to be an event based on another random event then behavior would become even more mysterious.
Fair enough. Can now understand that neuron might just fire without itself or anything else "choosing" to? Because of sodium continually leaking in? Or perhaps because of some random events? Yes, that too will come up, and makes the thing even more interesting (more mysterious? or less so?). PG
It is important to spend some time understanding potentials and permiabilityin the axon of the neuron, to understand behavior. These two fundamental processes are what run the mechanism of communication through the > entire nervous system. Potentials such as the action potential and resting potentials together are what is responsible for information flow through the axon. In this sense, it can be said that potentials are the essence of the neuron. Permeablitity, is what causes potentials in the neuron. In the axon, certain ions are less permeable than others, this causes a concentration gradient, and a region of the axon which is more negatively charged. This negative charge attracts opposing charged particles and repels similar ones. This particle rearrangement causes a more positive adjacent region. This more positive region allows for the permiability of more ions, and another concentration gradient to develope. This is what is meant by information flow through neurons. Understanding this concept makes the complex theories of behavior more simple. One can now view behavior as the result of information flow through neurons in the nervous system to and from the brain. All forms of behavior can be seen as the result of actions potentials traveling down axons of neurons to communicate with other neuons.
Does indeed give us a common set of concepts for dealing with all forms of behavior. Be a little careful though about getting the details right. The concentration gradients aren't caused by the permeabilities or by the membrane potential differences. The concentration gradients are primary, and produced by pumps in the membrane. The potentials result from diffusion down the gradients across semi-permeable membranes, they change because permeabilities change, and the permeability changes occur in part because of changing potentials. Got all that? PG
We can now account for behavior at a deeper level than we could a week ago. We can describe the physical nature of the action potential, its speed and direction. We can see how inputs are taken in and hypothesize about how outputs are sent out. It is worth spending a week understanding these components of behavior, because we can now refer to the generation and journey of the action potential in our explanations with confidence that we are understanding each other. However, it is dangerous to assume that we have reached the most basic level of explanation for behavior. The questions brushed aside in class for lack of time, or answered with the classic explanation that we just have to accept that this-or-that exists and functions in such-a-way, are valid questions indicative of an underlying body of revelation even more important than solving the mystery of the action potential. We must remember that scientists spend lifetimes on this more intricate problem and never fully understand it. It is understandable that we need to move on due to the time limits of this course, but we must first acknowledge that something is still missing from our explanation. Like an elementary school student who is told that photosynthesis happens but is not entrusted with the explanation for such magic, we are left with a greatly simplified, basic body of knowledge. Our danger is that we should build on such knowledge without delving further into it, or use it as an excuse rather than an explanation.
Legitimate general concern. Were there specific questions "brushed aside"? If so, I apologize, and its worth taking the time to at least see what the general class of such questions is so we know what foundations might be shakey. There are indeed questions about boxes inside the neuron (how permeability changes, how pumps work, and so forth) that lots of people are productively spending lots of time on. Are those what are concerning you? If so, I agree we didn't have time to go into them in depth, and that is a deliberate (though not dismissive) choice reflecting a belief that we actually know enough about them at the moment to take a fair crack at problems at a higher level of organization. At the same time, it is certainly worth looking at how stable one expects that foundation to be. PG
I believe that in order to understand behavior, which we have determined is the nervous system, we have to start at the most basic element of the NS and understand how it works. In other words, yes, it is worth spending a week (and even more) on learning about potentials. Once we discover how neurons relay their signals, we can observe how an individual is affected by these signals, and what kind of signals (or which) are produced by certain behavior. These observations may provide information that could enable us to explain simple behavior in terms of potentials; the explanations of the simple could help us understand complex behavior in the same terms (potentials).
I think you're right, but its interesting to try and understand exactly WHY this is so. After all, one could use the same (basic element) argument to say that we really ought to be starting with carbon, hydrogen, and oxygen. How does one guess where to start? And how decide whether one has started at the right (or at least a useful) place? PG
Over the normal sunday night dinner and ice cream bar, I was discussing with my friend whether learning about the microscopic events (such as an action potential) is essential for learning about the whole. She was quick to reply that the whole is much more important and hence, we should study the whole and spend less time on the smaller pieces. I thought about that and I made an analogy to that of working with a puzzle. It is true that the finished product, the whole puzzle, is the goal, but in order to reach that, you must examine, shuffle, and fit in place the small pieces. Eventually, everything falls in place, and a clear picture emerges. This is similar to behavior; we have to understand what happens at every neuron in order to string the neurons together which in turn creates a pathway for behaviors to be communicated and understood. So....the answer to whether it is worth spending a week on action potential is a big Yes for me. Although it is hard to grasp the concepts because they are occuring so frequently and on a level that the human eye cannot see, it is these action potentials that are the reason we have movement, thought, etc. You simply can't learn about one without understanding the other. If I follow this reasoning then, because we have no clear answers to behavior, we still have issues with action potentials and small events that have to be dealt with before behavior can be more clearly explained.
I waslooking at the class's essays from last week and, after reading Erin Brown's about the paralyzed friend who had cut himself before the race and wasn't aware of it, I started questioning just how action potentials occur. If there is no leg movement, that can't mean that there are no action potentials, can it? Does this mean there are only resting potentials in the affected limbs and, since there is no movement, there are no action potentials? (now I am REALLY confused). Is it possible that there are different types of action potentials that cause different types of behavior (just a thought)? For example, one action potential causes movement whereas another action potential causes feeling, etc.--I'm not sure if this makes any sense. Also, while in a biopsych tutorial, we were discussing biofeedback, and that makes me curious about how action potentials are affected by such practices as Chi. If we can control certain behaviors, then we must be able to control the smaller steps that make up behaviors.....so does this mean that we can control our action potentials?
Regardless of all my questions, I do believe that any class that plans to investigate and possibly understand behavior must spend time learning the cellular steps--without these, the behaviors will never exist.
Very interesting/thoughtful, thanks. The parts versus whole issue indeed turns up in lots of contexts ... and has, I think, a general answer as you've give it. Properties of parts may (or may not) be directly responsible for properties of whole, but are, at a minimum, necessary to understand what properties of whole are conceivable (since they must derive from properties of parts). And, in this case, some more immediate significances to properties of neurons. No, there AREN'T different action potentials for different behaviors. They're all the SAME action potentials. So how can there be different behaviors? Or movements sometimes, not others? Good question. What it must (and does) imply is that not only the properties of the neurons (action potentials) but also how the neurons are organized and interact is a key factor in behavior. As we'll talk about. PG
Was it worth an entire week of class to reach a better understanding of how potential is generated in a single cell? In my eyes, by all means, ofcourse it was. Why does Bryn Mawr makke every freshwomen take a liberal studies english class their first semester? In my eyes, it is essential foe everyone in such a class grouping to start off on a generally, similar first step. Only is the very basics are agreed upon and recognized can a class begin to build arguments and more in depth theories. And besidees, I'd hate to think that all those weekly liberal studies I turned in as a freshwoman were worthless. :)
I also think it halps to have recognized on such a small cellular, iceroscopic level because, often it is difficult to relate something so macroscopic as physical behavior to something within the human nervous system, so minute. Understanding the signaling process due to close proximity which neurons display lends a helping perspective on just how electric and quick reactions within the human nervous system take place.
The downfall however of spending so much time on the actual speecific mechanism of behavior takes away from it's mysterious qualities. I aam one who likes to think that each person in the world is unique, appreciate it, and not ask into too much depth...why.
But maybe looking in depth turns out to enhance the sense of uniqueness, and the appreciation of that? Common first steps are useful, particularly if they lead on to an understanding that similar first steps necessarily point on to uniqueness? PG
In class on tuesday, you said (roughly) that if we plug the sensory output from the eyes into the input for auditory processing, we would "hear the lightning..." I think I understand your drift, but am getting caught up on the neurological details, and my fuzzy recollection of visual processing. The point you are making, as I see it, is that neurons all communicate using the same language moreorless regardless of the origin. The notion of sound comes from the fact that input from the ears goes to a certain area of the brain that has evolved to recognize its input as correlating with rarefactions and compressions in the air (i.e. the physical manifestation of sound) So the answer to what happens when a tree falls in the forest but no one is there to hear it, is that the tree causes compression and rarefaction in the air that vibrate out in all directions, but no "sound" is "heard", because hearing is that act of the brain interpreting input (action potentials and partial depolarizations) from the ear as sound. Sound is the word used to laebel the brain interpretation... IS this pretty much waht you are driving at? That we can change a sound into a sight just by changing which part of the brain receives the input?
Yep. Pretty much. Exactly, in fact. With the resulting implication that to understand behavior one has to worry not only about action potentials but also how neurons are connected to one another. PG
As in every other living system it is necessary to understand the smallest details of how the components of it work in order to understand the system as a whole. Before we knew about cellular respiration we knew that in order to survive we need to breathe oxygen, but didn't know why or how it is used. Similarly, we know that we behave and we know that electrical potential in our neurons has something to do with it. We need to find out how exactly behavior emerges from potentials, just as we needed to know how oxygen provides us with the ability to continue living. "Life" itself is a product of molecule, atom and ion interaction and to understand all aspects of it we need to consider and closely examine these relationships. Thus, it is worth devoting time, however much is needed, in order to understand electrical potentials in nerve cells and resulting behaviors.
The problem with that argument is that it doesn't give one much guidance on how small one has to get, nor on how much time one should spend on the small. There are always more things one could learn and always smaller things to study. How decide? PG
Examining the nature of the generation of action potentials in single cells to better understand behavior implies that abnormal behavior should be associated with abnormalities in the behavior of neurons. In a sense, this approach to studying behavioral neurophysiology views the nervous system as an information superhighway for our bodies. In addition, all behavior, both internal (unobservable) and external can be conceptualized as forms of communication both within our bodies from one structure to the next and between ourselves and our external environment. At the basis of these communications is the neuron. The observable/measurable behavior of the neuron takes the form of the action potential. Disruptions in the behavior of neurons can take a number of forms, but essentially in each case, there is a disruption in the communication of one neuron to the approximately 1000 neurons onto which it projects. The ultimate expression of that neuron/the end product of its action potential is the release of neurochemicals into the synaptic cleft. Therefore, a disruption in the generation of potentials should be expressed in altered levels of neurotransmitters being released. This disruption in communication amongst neurons should correlate with disruptions in a person's overt behaviors.
One example of a breakdown in affective and cognitive behavior that is associated with altered levels of neurochemicals is schizophrenia. Studies of schizophrenics have found a correlation between the negative symptoms of schizophrenia and a decrease in metabolic activity and a decrease > in dopaminergic activity in the prefrontal cortex, a condition referred to as > hypofrontality. Axons from cell bodies in the VTA comprise the MFB, and their terminal endings project onto the prefrontal cortex. One of the structures with which these dopaminergic endings synapse is the nucleus acumbens, a mediator of attention and reward mechanisms. In people not suffering from schizophrenia, the EPSPs from glutaminergic neurons, which synapse with the the dopaminergic neurons at the nucleus acumbens, ensure what is referred to as a tonic release of dopamine. However, in schizophrenics there is a decrease in activity of glutaminergic excitatory input to the dopaminergic neurons resulting (characterized as phasic rather than as tonic) in an subsequent decrease in the release of dopamine to the synaptic gap at the NA. This decrease in mesolimbic dopaminergic activity is associated with the negative symptoms of schizophrenia. Conversely, one hypothesis to explain the positive symptoms of schizophrenia is that due to the decreased dopaminergic activity at the synapse, the DA receptors in the nucleus acumbens actually become more sensitive.
Numerous other examples of how behavioral dysfunction correlates with neural communication gone awry -- Parkinson's disease, the frozen addicts, and even sociopathology to name a few -- exist. What these examples imply is that by examining abnormalities in the outputs of individual neurons, the biological source of the disruption in behavior can be found. In other words, altered single unit activity can communicate to a doctor the possible disruption of specific structures, > regulatory mechanisms, or even the generation of potentials themselves.
Nice and important examples of the material basis of behavior. Interestingly, it comes from a tradition, neuropharmacology, which doesn't strictly depend on knowing how action potentials work ... and in fact didn't pay much attention to that for a long period of time (perhaps appropriately). We'll talk a little about the relation between the two traditions in the next lecture, as it happens. PG
Since we have already concluded that brain is behavior, we need to understand how the brain works to generate behaviors. It is worth spending so much time understanding potentials because they are the source of our behavior. I find it intriguing that we know so much on such a very small scale. We can better understand behavior if we study such small details.
Even by knowing about these small boxes, there still seems to be a lot that we do not know, or that we have not yet touched upon in class. One neuron needs input from another neuron to have an output. And for a particular sensational input, there needs to be thousands of intermediate inputs and outputs for a sensational output to result. How can there be so much order, yet at the same so much variability to the nervous system? Changing permeablities.... thunder and lightning.... there is so much precision. I think that it was you who said that the internet is like a complex brain. But I am not so sure that anything can be more complex than the brain. Nothing artificial at least. It would be amazing if we could create something that has the ability to learn for itself over time. And display autonomy as well. Only by understanding every little piece of the brain, every little box, can we eventually lead to a better understanding of behavior. Who knows, maybe then we can create behaviors in other ways than we are used to...
Indeed, there is a LOT we don't yet know/understand. Which is to say that we need to know (as you say) not only how the smallest boxes work but how they are interconnected and talk to one another. "Order AND variability ..." An interesting (and quite general) problem (evolution, the immune system, society?). Am not sure best approach is "understanding every little piece of the brain". Are too many, and run into not seeing forest for trees problem? But yes, maybe create (or at least influence) behaviors in new ways. PG
It is important to understand the ways in which the electric potentials travel through the neurons, because the electric signals are what enables the neurons to communicate with each other thereby creating the informational network that transmits the information from sensory neuron the motor neuron. To understand the electric potentials and the sodium potassium pump and the concentration gradiates is to understand one aspect of neuron action. What interests me now is how axons and dendrites communicate through the synaptic cleft and how the electric impulses interact with neurotransmitters.
Fair enough. Will get to most of that. PG