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Nerve cells

  1. Mar 6, 2005 #1
    Why are neurons shaped the way they are?
     
  2. jcsd
  3. Mar 6, 2005 #2

    Monique

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    What part of their shape do you mean? They are long, since they have to stretch over long distances, they have a bulky head to accomodate the nucleus, they have an synaptic disk to optimize surface area contact, they have many dendrites to receive signals from other cells..
     
  4. Mar 6, 2005 #3

    saltydog

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    Interesting question.

    Neurons as all other biological components have a long evolutionary history. From that perspective, the particular design of the neuron arose in short, by selective pressures operating on chance designs, weeding out the less favorable designs. The particular morphology of the neuron as it is today represents millions of years of selective pressure favoring the best design of a cognitive faculty which optimized the survivability and reproducibility of the organism within the constraints imposed by chemical and physical means.
     
  5. Mar 6, 2005 #4
    I see so they have evolved to be this way thats cool.

    They recieve signals from other cells from their dendrites but why? Why do they exist? Let me try to answer this first...

    Well our nervous system is made up of these neurons and the brain makes commands which travel as signals along these neurons? and the neurons give these signals to other neurons and or muscles? To perform a specific function? Like muscle contraction?

    Are neurons located anywhere else? and by shape I mainly meant why is the axon so long? and why are dendrites branched out (probably so they can increase surface area and recieve as much signals as possible?)
     
  6. Mar 6, 2005 #5

    saltydog

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    They exists because they contribute to persistence of being. You know, individuals with superior neural consructs better survived and reproduced than those with meager ones: If two early hominids saw two lions entering the savanna and saw one leave, the hominid that could count would pass on his genes to the gene pool.

    Axons need to be as long as it takes to reach their terminal bud. I believe the longest in man is about 3 feet (from spinal column to big toe).

    The neural architecture (connections) gives rise to mind although some would argue other "forces" are involved, In general, the greater the complexity (extent of connections), the greater the extent of mind. A cognitive apparatus is a selective advantage to survival; one with greater complexity is more of an advantage within limits. Thus, through millions of years of evolution, the advantage of a more connected architecture drove our evolution towards greater neural complexity (more branching). The reason other life forms didn't evolve such complexity is simple: chance (we were lucky) and competition (we'd stop them).
     
  7. Mar 6, 2005 #6

    Moonbear

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    There is actually quite a lot of variety to the shapes of neurons. Dendritic and axonal branching (yes, axons can branch as well) is guided by other nearby neurons and adhesion molecules nearby.

    As you're asking questions in biology, think about whether you're really intending to ask "why" or "how." The question of "why" is usually related back to evolutionary processes, and can often be thought about with better clarity in context of "why not?" However, students often ask "why?" when they mean "how?"

    My brief answer above addresses "how?" There are a lot of people actively researching that question, if that's the question you really meant to ask. They are looking at the intracellular signaling, extracellular signaling, cytoskeletal responses, etc. The question is important for understanding other "how" questions, such as how do neurons form connections during development and ensure these are the right connections for the function they will serve, and how can neuronal connections be repaired after injury.
     
  8. Mar 6, 2005 #7
    Moonbear you're right I was asking more of a "how" question... "Why" they are shaped a certain way is because of biological evolution...

    Okay I understand that survival of the fittest thing (saltydog) but doesnt that hold true for all human cells? tissues? organs? not just nerve cells?

    What about the main function of neurons like, they recieve electrical impulses from the brain right? Im just wondering what they do basically......like.. the process of how they work in the nervous system..
     
  9. Mar 6, 2005 #8

    saltydog

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    Yea, JimmyRay, everything within us is affected by evolutionary pressures.

    You can google on that. Francis Crick wrote a good book called "The Astonishing Hypothesis" that a good read. Another good one is "The Computational Brain" by Churchland and Sejnowski. Tons more you know. Lots of chemistry. That's why I majored in Chemistry!

    Salty
     
  10. Mar 7, 2005 #9

    Moonbear

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    No, they are one of the cell types that form the brain. It's chemical signaling based on ion gradients.

    I wish I had seen this earlier before I was too tired to write out a lengthy explanation. For now, look up "action potential" to get you started on how neurons function.
     
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