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Friday, July 2, 2010

Part III: The Current Debate - The Electro Chemical Impulses of the Body

See Part I: The Current Debate: AC/DC Current under May 2010 heading
See Part II: The Current Debate: How Electricity Works at the Atomic Level under July 2010 heading


Part III The Current Debate: The Electro-Chemical Impulses of the Body
By Robin M. Strom-Mackey
"Thus the body utilizes DC power, electro-magnetic energy that moves in a straight line and not in waves – like AC power. "
Electricity in our bodies is different from the household current you use when you run your television or charge your cell phone. Electrical impulses in the body are a much more complicated electro-chemical reaction which utilizes ions versus electrons in order to send its signals.
Neural Impulses in our body run along our millions of nerve cells directing everything from digestion to muscle movement. The gray matter in your skull (and the white matter, for that matter) is clusters of nerve cells which send electro-chemical impulses from one part of the brain to another. Other nerve cells run down our spinal column and nerve cells run all the way out to our feet and hands, (the nerve cell that runs to your big toe is literally around 4 feet long) creating a two-way communication system from all parts of our body to our brain and back. As you do your Algebra homework, or try to figure out this article you’re using your nerve cells, also called neurons, which are processing information and sending out directions constantly.
Unlike the electrical current that is running through your computer, which utilizes electrons to do its dirty work, the body uses ions to send its signals from neuron to neuron. Ions, as you recall are the entire atom of an element that has either gained or lost an electron. Because of this loss or gain of an electron, or two, the entire atom is either positively or negatively charged. In the case of our bodies these ions are what creates the electrical-chemical impulses that keep our brain functioning and our bodies moving. These ions move about in and out of nerve cells, also called a neuron. As these ions move in and out of the cell they change the electrical charge of the cell. If you recall from your time as a youngster playing with magnets, the positive end of the magnet will attract the negative end of another. But try to put two positives together, or two negatives, and they repulse or push away from one another. This concept is essential to the way electricity functions both in your body and out. Essentially the body uses the positive ions (mainly sodium and potassium ions) to generate its electric charge. When at rest, the neuron body is slightly negative due to the large amounts of potassium (K-) ions in the cell – which are negatively charged. The space outside the neuron cell body is surrounded by sodium ions (Na+)  and the space is positively charged. When the nerve cell is stimulated enough, channels open along the outer walls of the cell. The sodium ions, which are positive, rush into the cell because they’re attracted to the negative charge of the potassium ions (K-).
A nerve impulse depends on an electro-chemical reaction to occur to actually start a nerve impulse. If a stimulus is strong enough at the receiving end of a neuron, called a dendrite, a neuron will send a neural impulse called an action potential. When the stimulus reaches the threshold, (i.e. when it’s a strong enough stimulus to warrant action) channels, in effect doorways, along the neuron cell body open up and sodium ions begin to flood into the cell body. During an action potential the cell body becomes positively charged and the area outside the cell body becomes negatively charged. The action potential moves along the neuron cell body to the end. Once the impulse has passed, the neuron resets itself, essentially pushing the sodium ions back out and pulling potassium ions back into the cell until it reaches its initial resting state. Once a neuron fires it cannot fire again until it has reset itself –which is known as the refractory period. An action potential runs in a straight line and in only one direction – it does not double back on itself. Once started it does not stop until it reaches the end of the neuron at the axon terminal. Thus the body utilizes DC power, electro-magnetic energy that moves in a straight line and not in waves – like AC power.
A neuron - The branches off the green neuran body are the dendrites, the receiving end of the neuron. A stimulus detected here generates an action potential which moves through the cell body and down the long axon (shown in red) out the axon terminals at the bottom.
Now neuron cells don’t actually connect to one another. At the end of the neuron – the axon terminal - the action potential stops because it’s hit the end of the road. Between the axon of one neuron and the dendrite of the next neuron cell is a small empty fluid filled area that must be breached in order for the action potential to continue on its merry way to the next neuron cell. This fluid filled cleft is called a synapse or synaptic cleft. As the action potential hits the end of the axon, small pouches which hold chemicals, referred to as neurotransmitters, are motivated to spill their chemicals out of the neuron cell body and into the synaptic cleft. As these chemical atoms spill out they drift through the cleft over to the dendrite of the next neuron, where they attach to docking stations – called receptor sites - on the dendrite, causing this neuron to begin the action potential in the new neuron.
Neurotransmitters, by the way are very much like keys and receptor sites on the dendrite of the next neuron like a locked door. You need the correct key (chemical) to open the door. Remember the last time you forgot which key was to which lock, so you had to try all the different keys. Some may seem to fit as they slip them into the lock, but try to turn the knob and it just won’t work. Neurotransmitters work exactly the same way. Just the right chemical key and the dendrite is excited, sodium ions begin to flood in and an action potential is generated in the next neuron. Try the wrong key (neurotransmitter) and the neuron doesn’t fire. As complicated a process as this appears to be, a neuron can do all this in a fraction of a second.
 
You may be asking at this point why our neurons don’t use electricity versus this complicated electro-chemical process. The answer is that we do actually have some neurons that fire with electrical impulses – and yes it sends impulses faster. But 99% of our neurons use the action potential impulse, and movement of ions in and out of the neuron cell bodies to move impulses along.
References
Hockenbury,D.H., Hockenbury, S.E., (2010) Psychology 5th Edition. Worth Publishers: NY, New York.
Malone, L.J, Dolter, T.O. (2010). Basic Concepts of Chemistry; Eighth Edition. Wiley and Sons, Inc.: Hoboken, NJ
Marieb, E.N., Hoehn, K. (2009) Human Anatomy and Physiology; Eighth Edition. Pearson Education, Inc.: San Francisco, CA.

Physics: Electric Current Through Various Media Downloaded July 2, 2010 from Wikipedia at http://en.wikipedia.org/wiki/Electric_current









2010 heading

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