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Neurobiology and Behavior, Week 5
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. Leave whatever thoughts in progress you think might be useful to others, see what other people are thinking, and add thoughts that that in turn generates in you.
As always, you're free to write about whatever thoughts you add this week. But if you need something to get you started, what do insights into both the nervous system and behavior come from understanding action potentials, resting potentials, receptor and generator potentials, and synaptic potentials? Does an understanding of the nervous system at the cellular level make it seem more or less possible that brain = behavior?
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A Random Walk
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Babies and I-function
Whether babies have an I-function when born leaves me thinking yes and no. In the beginning of the semester we talked about babies carrying out the experiment for hunger. Cry someone comes and gives a bottle, cry again and they maybe perform another task. This makes me think that babies at some point realize and can claim to feel hunger. Also when babies are first born they are slapped on the butt and then cry. Now is this because of pain or does this act allow for any fluid that was initially clogging vocal passages to be unclogged and the sound waves are no longer blocked? I ask this because I routinely observe younger cousins who will fall or bump into something but not cry or fuss until attention is brought to it. Based on these observations I would say that babies are not born with an I-function and become aware of certain pains, etc. through some what learned behavior.
Comparing an action
Thinking of an action potential in this way can perhaps help explain how some input can have no output. If the cell membrane is not depolarized enough (ie it does not reach the threshold potential) an action potential will not be generated, it thus the input may not have an output. I know that this threshold potential can vary (within a certain range). Could this be the reason why some people react to certain inputs and others may not?
Is locked-in syndrome
brain chemistry
Backward and Forward Action Potentials
I too was very interested in the idea of an action potential possibly being able to evade the nervous systems preventative mechanisms, such as ion channel desensitization, and unintentionally propagate in more than one direction. As discussed by Brie, I think this is a very probable explanation for certain nervous system disorders or conditions which are associated with neuronal ‘misfiring’. What if we could explain some ailments by the fact that an inadvertent, backwards propagating signal is colliding with an intended, forward propagating signal in situations where desensitization of things like sodium channels did not effectively prevent the transmission of this action potential in the reverse direction? In the event that this does occur, what would be the effect of two oppositely oriented action potentials moving into one another? Would these two effects compound one another and create an isolated, overly robust signal at a given point in the transmission pathway? Or would the two cancel one another out, thus preventing the intended transmission of the nervous signal which would lead to the inability to generate muscular movement? If the latter is the case, are there documented incidences where conditions like paralysis have been caused by the inability of the nervous system to consistently prevent backwards action potentials from being generated and not the severing of the various pathways which compose the nervous system?
Pain and Behavior
The discussions on action potentials and pain reminded me of an episode of Grey's Anatomy which aired a few years ago when the series was actually worth watching. In the episode, "Sometimes A Fantasy", a girl is brought into the hospital with a history of injuries. Alex, an intern, believes that the girl is a victim of child abuse, an all-too common and an unfortunate reality of foster care. However, by the end it is revealed that the girl has a rare genetic disorder which causes her to be insensitive to pain. Due to this insensitivity, the girl believed that she was a superheroine and often dared classmates to injury her (i.e. baseball bats to the stomach) in order to prove her superhero status hence her numerous injuries. This idea of pain insensitivity prompted me to research its connection to behavior. Do people who suffer this rare but real-life condition have notions of indestructibility? My research led me to a National Geographic article (link provided below) that elucidated the issue at hand. The article revealed that a mutated gene found in a population located in northern Pakistan could very well be the cause for the disorder. This mutation inhibits the function of a protein responsible for crossing charged chemicals to the surface of nerve cells by forming channels for the which the chemicals could cross. Apparently, the deactivation of the protien affectively deactivates stimulation of the particular nerve cells responsible for sensing pain and not those responsible for sensing pressure, temperature, or shapes.
What I find most intriuging about the article is its connection to behavior. The boy who clued the researchers into the genetic disorder unfortunately died after jumping off a house--perhaps implying that he had an episode of false indestructibility. A man who reached 20 years of age before he was diagnosed proved to be more lucky. Watching other people's reactions to situations involving pain allowed him to figure out what to do and what not to do in certain situations. Take for example, being electrically shocked while wiring. His arms started to shake with the voltage coursing through his body. At first he thought it was funny then he realized that perhaps this was not an appropiate outcome of wiring. Though he felt nothing, he was left with burns on his hands. I marvel at the idea of having to learn a behavior when normally, this reaction is under the responsibility of reflexes first initiated by the sensation of pain.
http://news.nationalgeographic.com/news/2006/12/061213-pain_2.htmlDifferences in Pain Tolerances
To comment on the the
To comment on the the discussion in class about how people react to pain, I feel like people usually withdraw from painful experiences because most of the times they are accidents. For instance, most of the time people accidently do things that cause pain, but at the same time they see the pain coming so prematurely begin to withdraw.
From what i remember in biology for an action potential to occur, there needs to be a certain threshold that is reached to begin the propogated diffusion of charged particles. What I'm interested in is how do people have different pain thresholds. Whats makes some people feel pain more strongly than others. Why for the most part do males have higher pain thresholds for certain activities whereas women have higher pain thresholds for others?
understanding of the nervous system at the cellular level
Understanding of the nervous system at the cellular level makes it seem more possible that brain=behavior. Any defect in neural system would cause deviation in behavior. This time, I would be curious to know how the neural pattern of the visual person’s brain is different from that of auditory person. My close friend who is more visual than I am doesn’t remember what words I used when I speak, whereas, I am forgetful in images I saw. My friend seems to remember things in chunks of images whereas I remember incidents in forms of language or person’s voice. , I would imagine that there are more numbers of neurons in the part of the brain where visual processing occurs for a visual person and vice versa. As I read the posts above, I found reading about different reaction time. In my case, is it about the faster reaction time or action potential rate in that region regardless of numbers of neurons? Because each person with different characteristics seems to have different arrangement/pattern of neurons in the brain, again, understanding the nervous system at the cellular level makes it seem more possible that brain=behavior.
thoughts on the "positive-feedback" loop
Chemicals
It seems the more we learn the less we know about the brain. Why is it that brain activity is so often portrayed as an electrical current when it is in fact a chemical one? It is interesting to note the inherent misconceptions about the brain that we must address. No electricity in the brain, ok, that makes sense based on what we have described as an action potential, so how else has so called 'common knowledge' tricked us? Are there spaces between the neurons, what lies between them?
How does the movement of chemicals create our thoughts? It's strange to think that the mere shifting of voltage in small areas can create such amazing things as our thoughts. I know there is more to it than that but how, how can these thoughts be just the movement of chemicals along a path. How can the act of writing this post be an action potential along an axon? Is this complex process just chemicals?
there's gotta be more to it
This is my third or fourth time learning about action potentials and how they produce our body's output and process input. It still amazes me how our body is run by these electrochemical waves of activity, and I am still hesitant to accept the fact that these electrochemical signals are the whole story.
One of the main reasons why I cannot accept that everything we do is a result of these action potentials, or brain=behavior, is because we have thoughts. This goes back to the question of how consciousness can arise from physical material, which is a fundamental question that is the root of most questions in neurobiology. Do these chemicals and electric currents give rise to our thoughts and self-awareness as well? Or are they only responsible for our reflexes and behavioral responses to the environment. As complex as action potentials and chemicals are, I feel like they are still too simple to explain consciousness.
Moreover, several people have commented on how there can be input signals without outputs and output signals without clear input signals from the environment. The mind, or thoughts, can motivate behavior independently from the environment. In these situations, mental thought is the input signal for an outward behavior. So how does this mental force trigger a series of action potentials? What is the chemical make-up of a mental thought?
Understanding the cellular basis of how the nervous system works tells us a great deal about the intricate design and function of the nervous system. However, I don't think it provides the whole picture.
Kind of, but not really
big picture
symphony
I-Function Disjunction
The notion that one's "I-function is not equivalent to the self" is really interesting to me, in the sense that one's personality and sense of selfhood is comprised of many more factors than merely their conscious actions, which the I-function is responsible for. Thus, I am still pondering what these other factors are...
Also as far as the I-Function's role (or lack thereof) in executing actions , I am still struggling to understand the concept that when one actually thinks about the action taking place, it actually has an adverse impact on the efficiency of its execution. For example, I have been running track for several years. In high school I was a distance runner but became a sprinter in college. A concept I had to become accustomed to was the idea that lifting your legs higher actually helps you go faster and further. So, often during a race my coach would be shouting to me from the sidelines to "pick up those knees!"-thinking about it and doing it was usually the main reason why I would decrease my times and improve my personal bests, eventually qualifying me for conferences. Also when I bike, especially in the city, I do think about what I am doing-how fast do I need to pedal to make this light? How busy is this intersection-can I weave through these cars and pedestrians? “OK the light just turned red, how little can I decrease my speed to avoid coming to a complete stop and losing my kinetic energy while waiting for the light to turn green again?” I find that it is this very thoughtfulness and awareness that has allowed my success and safety, be it running, biking or otherwise.
As far as muscle memory is concerned, I am sure that that accounts for part of it as these activities do feel very "second-nature, " however, I am more so concerned with the mental thought processes as I disagree that use of the I-Function impedes the execution of an act.
micro to macro
Reaction Time
I remember learning about the concept of reaction time in physics class, but never understood the biology behind it. From what we learned in class I would assume that reaction time results from the time it takes for an action potential to travel down an axon.
I think reaction time connects to the exercise we did in class where we proved through a computer program that it takes time to think. If thinking involves neurons, then it must also involve action potentials, which take time to travel.
Thinking about reaction time has raised a few questions for me. I know that reaction time is different in every person (and animal) and that one person can have several different reaction times to the same stimulus. But, I wonder why? Can the action potentials travel at different speeds?
behavior=action potentials?
practice to instinct
It now makes more sense to
It now makes more sense to me why thinkng sometimes makes me unable to do things. I'd always noticed that i couldn't do certain things, like driving or playing sports, if i thought about what i was doing, but i'd never thought about the reason. maybe it is simply that thinking, or sending signals around in the "I-funtion", takes time, and when there isn't a lot of time the signals have to be sent dierectly to the muscles and skip the i-funtion.
on a side note, i just read an article about how colors affect the brain. apparently red makes a person remember details and blue inspires creativity.
http://www.cbc.ca/technology/story/2009/02/05/red-blue-colour.html?ref=rss&loomia_si=t0:a16:g2:r4:c0.0384407:b21688921
just thought that was interesting
Week 5
Recently the media has focused on stressful life events, like losing a home, that have had a profound impact on mental wellbeing (guardian.co.uk). "Recession depression" has caused many people around the world to experience feelings of anxiety, depression and severe mental illness. As we continue to struggle through the financial meltdown, there is no denying that both the brain and mind contribute to behavior.
At the end of class, we
I, also, thought about the
I, also, thought about the potential for differences in the firing of action potentials among people. Once an action potential has been fired, does it travel at exactly the same speed? Do people with shorter legs have action potentials that reach the projection of the neuron earlier than those of people wiht longer legs? (probably a negligible amount anyway....)
What about processes of which we are not conscious--breathing, blood-pumping, shivering? Do some people perform these acts at negligibly different rates based on action potentials? Probably. It doesn't seem like these differences would be worth noting, though, given how infinitely small they would be and the fact that an action potential is not something created by the mind or by behavior. We cannot really see the direct result of an action potential--we see the secondary results, which may actually vary in timing in a visible way.
Electrochemical Change=Behavioral Change?
In discussing potentials this week, I had one group of ideas that came up:
Like many natural systems, the nervous system remains very very complex. With newer technologies, the investigations of the nervous systems seemingly reveal more complexity and subtlety to processes that we perceive from a technologically-banal perspective as simple. For instance, the knee-jerk reflex that we're all familiar with at the doctor's office now seems to involve many many parts and mechanisms, not to mention my conscious response of viewing my knee jerking. Specifically, the reaction would involve the use of polarization/depolarization of neurons with resting and active potentials, and then the connection between that action potential to the motor neuron (output) to stimulate a reflex. Undoubtedly, many of these physical effects (e.g. potentials) result in an effect on behavior, however, what is the value of a physical effect on a behavioral result? In other words, does the magnitude of polarization/depolarization have a correlatively effect on behavior (e.g. a strong depolarization having a strong muscular reflex)? Or, should we follow the stimulus-response model in that every (physical) input, even if it is the consistent, may have a completely random (behavioral) output?
I guess professional neuroscientists spend their life trying to elucidate those patterns, and the consistency or lack thereof of order.Reaction Time
Whenever I've been close to stepping on something painful or running into something, I've always noticed the little delay before my body reacts to what I'm seeing. Instead of knowing that propagation is occurring and that all of these reactions are attempting to get me out of harm's way, I've always just thought that it was the surprise that caused my hesitation. If you see a thumbtack on the floor and you try to dodge it, it's normal to assume that its appearance startled you and that's why it took you a second to react. Now that I am aware that it's not surprise but more a timed reaction I'm curious to what happens when you really are surprised by something dangerous. Is that why some people are "frozen" when they are about to be in a car accident or something equally dangerous? Are their action potentials slowed because of the surprise, adrenaline, etc. or is something different preventing reactions?
While it’s hard to fathom
While it’s hard to fathom that there are so many transmissions of action potentials running at one time in my body, I do understand the whole process of the transmission. The analogy of a battery was interesting to me, because I hadn’t thought of a concentration gradient with charge in that sort of fashion – but, it did make more sense.
At the end of class, we began talking about how propagation could go either way. The three stages of the sodium channels provided that the propagation channels did significantly move only one way, but I wonder, are there ever cases when sodium channels fail and propagation does go both ways? What is the resulting “output” of this skewed action potential? Perhaps this could relate more-so to explaining things like epilepsy or other seizure disorders that are caused by the nervous system going a little “haywire.” Maybe membranes disallowing some ions to permeate when, in reality, the ions should be entering into the system.