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Thread: The Nervous System

  1. #1 The Nervous System 
    Forum Freshman PPonte's Avatar
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    Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells. Schwann cells serve as supportive, nutritive, and service facilities for neurons. The gap between Schwann cells is known as the node of Ranvier, and serves as points along the neuron for generating a signal. Signals jumping from node to node travel hundreds of times faster than signals traveling along the surface of the axon. This allows your brain to communicate with your toes in a few thousandths of a second.
    Would someone explain me, please, the sentence in bold?
    My doubt is why signals jumping from node to node travel hundreds of times faster than signals traveling along the surface of the axon.

    Thank you.

    PP. :-D


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  3. #2  
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    as a current jumps over a gap, it speeds up. thats phyics methinks

    i guess they mean that its faster jumping , than going along with out gaps


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  4. #3  
    Forum Freshman PPonte's Avatar
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    I like Physics :-D, thus my doubt.
    If the signal jumps, the space that it travels is bigger than the surface of the axon. Isn't it? Or it doesn't jump, but "teleports" from node to node?


    i guess they mean that its faster jumping , than going along with out gaps
    Why is faster jumping? To jump is necessary some force. Is there a canon? :-D
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    hmm, i don't know anything about the central nervous system, never even heard of Axons or nodes..

    Cells are the nodes right and the receptors (nervelanes) are the axons right?

    it's obvious that signals go faster trought specially designed cells to get information there faster.

    anyway, more info could be usefull... hehe grr, specialised in biology and i don't know the brain.. how bad....
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  6. #5  
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    "Everything should be made as simple as possible, but not simpler."
    ~ Albert Einstein
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    sorry, what i meant was that phyics has the answer as to why electric currents move faster as they jump. i can't remember.

    transformers do the same job on our powerlines,
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    goodgod3rd, I read this site about the transformers: http://www.physlink.com/Education/AskExperts/ae427.cfm .
    Nevertheless, I could not relate the information to why electric currents move faster as they jump.
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    I think you are mistaken. I think the sentence you put in bold deals with chemical signals and not electrical. Although electrical signals exist, most of the neurons in the brain use chemical because it is more flexible (can be exhibitory and inhibitory). Electrical signals are only used for reflexes (like when you put your hand over a fire and your hand snaps back before you can think it).

    If you were talking about chemical signals, myelin sheaths speed things up because it acts as a barrier to sodium. When an action potential is generated, sodium moves into the axon through a channel. The sodium then diffuses along the INSIDE of the axon, upping the membrane potential closer to the threshold, and this causes the sodium channels AROUND it to open (sodium channel is voltage gated), which lead to the propagation of the signal. Normally the sodium quickly diffuses out as it comes in so only the sodium channels very close are able to reach the threshold and open. But when a myelin sheath is present, the channels are only at the nodes of Ranvier, and the sheath prevents the sodium from diffusing through the membrane so it only has one exit once it enters the axon and that is through the inside of the axon. Therefore, the sodium is allowed to diffuse along the entire length of the myelin sheath without losing much strength. (Remember, its not enough that just one molecule of Na be present, but enough to go over the threshold).
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  10. #9  
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    Sorry sTrumped, but I think you're first paragraph is all wrong.

    Neural activity within cells is all electrical (in the form of movement and conductance of ions). This is the same in the brain as it is in the peripheral nervous system (the reflexes you mention). However, neural activity/information is transmitted and modified BETWEEN cells through the use of chemical messengers. These are called neurotransmitters and are released for presynptapic compartments near synapses from neighboring neurons. The type, amount and distribution of neurotransmitters the are released near the synapses of a cell will influence how the cell responds electrically owing to its particular biochemical makeup.
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