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Muskaan Muskaan
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12 years ago
Why do nerve impulses move quicker along a myelinated nerve?
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how_mendelhow_mendel
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#1
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12 years ago
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Biology!

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#2
12 years ago
Neurones send messages electrochemically; this means that chemicals (ions) cause an electrical impulse. Neurones and muscle cells are electrically excitable cells, which means that they can transmit electrical nerve impulses. These impulses are due to events in the cell membrane, so to understand the nerve impulse we need to revise some properties of cell membranes
When a neurone is not sending a signal, it is at ‘rest’. The membrane is responsible for the different events that occur in a neurone. All animal cell membranes contain a protein pump called the sodium-potassium pump (Na+K+ATPase). This uses the energy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions in.

If the pump was to continue unchecked there would be no sodium or potassium ions left to pump, but there are also sodium and potassium ion channels in the membrane. These channels are normally closed, but even when closed, they “leak”, allowing sodium ions to leak in and potassium ions to leak out, down their respective concentration gradients
The combination of the Na+K+ATPase pump and the leak channels cause a stable imbalance of Na+ and K+ ions across the membrane. This imbalance of ions causes a potential difference (or voltage) between the inside of the neurone and its surroundings, called the resting membrane potential. The membrane potential is always negative inside the cell, and varies in size from –20 to –200 mV (milivolt) in different cells and species (in humans it is –70mV). The Na+K+ATPase is thought to have evolved as an osmoregulator to keep the internal water potential high and so stop water entering animal cells and bursting them. Plant cells don’t need this as they have strong cells walls to prevent bursting.
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#3
12 years ago
because the signal can jump between the nodes that separate the myelin bundles rather than traveling the full distance along the neuron
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#4
12 years ago
It insulates and moves the impulses along not in a wave, but in " saltations " of energy,. Does a couple of other things, things to do with resistance. A t wkipedia, under " myelin sheath ".
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#5
12 years ago
It's like any electric wire. If an electric wire is not insulated (has no covering) all other sorts of foreign matter may land on it. Dirt? Etc. Or metal which affects the transmission of the electrical signal.

So the myelin sheath acts as an insulation. Or else the electric impulse would be lost to areas outside the nerve.
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#6
12 years ago
Nerve impulses are far faster then responses to hormones. Nerve impulses involve the depolarization of neural membranes, which is as simple as the movement of sodium and potassium ions through channels. This is very very fast. The time this takes to happen is the time from when something touches you, such as your finger touching a keyboard to the time it takes you to feel that your finger is touching the keyboard. Another example of the speed of a nerve impulse is if you have ever accidentally touched a hot element on the stove, or a hot bowl and how fast your hand recoils. A nerve impulse must travel to te brain and back down again to tell your arm muscles to contract and move from the heat. This impulse is followed by a very brief period of non responsiveness but then the membrane repolarizes and the system can fire again. This whole process takes such a small time one could not measure it without special instruments

A hormonal response is slower and longer lasting. A signal must be sensed for a hormonal response, this could be anything from high or low sugar in the blood stream, to stress. Upon receiving this signal the hormone must be made. This is a time consuming event, as must hormones are proteins they must be transcribed and translated from DNA and appropriately processed in the hormone molecule. From here the hormone is transported into the bloodstream where it is distributed throughout, even though it may only act on certain areas, this is another time consuming process. For reference it takes the heart about 1 minute to completely circulate all the blood in the system, much longer then the fractions of seconds needed for nerve impulses. Once the hormones reaches its proper tissue it has its effect, which in most cases is a long and complex pathway, which can be turned on for a long period of time given that low concentrations of hormone can activate the pathway. Also another signal is also needed to counteract the effect of the pathway and turn it off. An example of this is adrenaline in a stressful situation, think back to a time where you nearly crashed your car, or went on a crazy ride at an amusement park, or something like that, the feeling of being on high afterwards is due to release of adrenaline also called epinephrine. The feeling does not occur instantly, but is still relatively fast and the feeling lasts well after the situation is over. Insulin in the blood stream is another hormonal response. When glucose is in high concentration in the blood insulin is secreted and travels through the bloodstream, it causes cells to have more glucose transporter at their surface so the high amount of glucose in the blood can move into cells and be used or stored. This is also a seemingly needlessly complex pathway involving at last 8 different reactions involving phosphorylation of proteins and lipid molecules, which certainly takes longer then the motion of ions through a channel.
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