how does demyelination of an axon affects conduction?
493330
The main consequence of a myelin layer (or sheath) is an increase in the speed at which impulses propagate along the myelinated fiber. Along unmyelinated fibers, impulses move continuously as waves, but, in myelinated fibers, they hop (or "propagate by saltation"). Myelin increases resistance by a factor of 5,000 and decreases capacitance by a factor of 50. Myelination also helps prevent the electrical current from leaving the axon and causing a short-circuit in the brain. When a peripheral fiber is severed, the myelin sheath provides a track along which regrowth can occur. Unmyelinated fibers and myelinated axons of the mammalian central nervous system do not regenerate.\n\nDemyelination is a loss of myelin and is the root cause of symptoms experienced by patients with diseases such as multiple sclerosis and transverse myelitis. The immune system may play a role in demyelination associated with such diseases. Heavy metal poisoning may also lead to demyelination. When an axon's myelin degrades due to these diseases, conduction can be impaired or lost.
388674
ONe of the greatest challenges is to delay or prevent the formation of the glial scar that blocks growth of new axons, thus inhibitors of cell division and reactive gliosis are primary areas.
122034
An impulse in an axon is like a wave of depolarisation on the neurone's membrane.\nWhen it reaches a synapse the depolarisation (action potential) causes the release, from the axon of the neurone, of a transmitter chemical.\nIt is the transmitter chemical that diffuses across the synaptic gap to bind with receptors in the next structure (another neurone or an effector, e.g. muscle) that causes the next event.\nSo the structures and mechanism at the synapse are rather like a one-way valve - the process cannot work in reverse.\nSince impulses are initiated in only one direction, impulse transmission in axons is always in one direction (though if you initiate an action potential in an axon experimentally it will propagate in both directions, but of course can only cross a synapse in one direction).\n\nBe careful with your use of the word 'nerve'. A nerve is a collection of many axons. There are some nerves which contain axons carrying impulses in opposite directions - these are known as mixed nerves.
766471
The function of a neuron is communication.\n1. Long axons allow for communication over long distances.\n2. The branching structure allows for communication between lots of different cells.
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Direct exposure to poliomyelitis virus of the central end of a cut branch of the V cranial nerve was followed by centripetal spread of infection to the semilunar (Gasserian) ganglion, involvement of which was detected both histologically and by subinoculation as early as the 3rd day. In some instances infection did not progress further; in others it spread into the CNS with initial involvement of the trigeminal centers in the pons and medulla as early as the 4th day and by the 5th day was further advanced but still limited to the brainstem. Once infection was established it progressed both rostrally and caudally, at times with great rapidity, through the brainstem and reached the cord on the 6th or a later day. Incidental exposure in traumatized muscle of peripheral fibers of the VII motor nerve led in some instances to spread along that pathway directly into the CNS.
999507
The flow of an impulse down a neuron is only one way ... so a nerve bundle would have to be oriented to receive a signal and send it down the pathway completely ... the neuron is designed in such where an impulse causes a Na/K Pump to initiate the movement of the signal across the axon.  As Sodium (Na) and Potassium (K) ions move across the myelin-sheathed axon, there is an internal mechanism which prevents the signal from retrograde movement.  This forces the impulse to move down the axon to the terminal points on the neuron.\n\nNerve conduction is dependent upon the individual neuron.  However, you should read the same conduction velocity on a given nerve at various points, keeping in mind that the myelination is equal along the path (myelin assists in the speed of transmission, less myelin means slower movement).  I do not believe that you can successfully send a signal up from the axon back into the nerve body, but I could be mistaken.
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The neuron actively builds the ionic gradients by pumping specific ions into or out of the cell.  Na+ and K+ are the major players, Cl- less so, and Ca2+ the least important.  Na+ ions are pumped out and K+ ions are pumped in by the Na+/K+ ATPase.  At rest, there are a lot of Na+ ions outside the cell and a lot of K+ ions inside the cell.  The charge imbalance means the cell has an electrical voltage across its membrane.\n\nWhen the neuron is activated, it opens up ion channels that allow these ions to suddenly flow into or out of the cell down their gradients.  For example, Na+ ions are suddenly going to rush into the cell and K+ ions will rush out of the cell slightly later.  The result is a sudden change in the electrical voltage of the cell membrane.  This is the basis of how nerves generate electrical impulses.
105755
I suspect it is a biochemical process. I skimmed the attached reference, and here is what I was able to pull out: \n\nThere is a complicated process that takes place in the neurons. Chemical action separates positive sodium and potassium ions from anions across a membrane, creating an electric field. Neurotransmitters open ion gateways in the membrane when the field is built up to a certain level. This allows an electromagnetic wave to travel down the nerve. \n\nIt is MUCH more complicated than that, but that is a simplified cartoon version of the events I think.
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It’s pretty much where excitatory and inhibitory signals are summated.  If there is enough stimulation to reach threshold the neuron fires an action potential here.  This is basically the first domino of a whole line.  Once it goes the signal travels down the rest of the axon, but this is where it starts.
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Multiple sclerosis is a disease caused by multiple areas of scarring in the white matter of the brain, causing loss of neural transmission or short circuiting, misdirection of neural transmission.  The symptoms can be quite varied among individuals with the disease, depending on WHERE in the brain their particular lesions are.  Malfunctioning neurologic symptoms can be blurring or double vision, loss of sensory of motor function in any variety of constellations.  \n\nSUMMARY:  It varies with the individual.
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"As the action potential envelops the bouton (the terminal bouton at the end of the axon), the synaptic vesicles attach to the bouton membrane at the active zone.  Once attached they release their chemical messenger into the synaptic cleft where it diffuses to the post synaptic membrane.  There the chemical messenger combines with a receptor protein, a process that alters the ionic conductance and consequently the membrane potential of the post synaptic cell.  This may initiate an action potential in the post synaptic neuron."\n\nTo summarize:\nThe action potential arrives at the synaptic junction.  There it stimulates the release of the chemical messenger, known as a neurotransmitter, into the synaptic cleft.  If enough neurotransmitter chemicals cross the synaptic cleft and attach to receptors on the 2nd neuron, a new action potential is initiated in the 2nd neuron.
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Well, take a look at this:\n\nhttp://www.answersingenesis.org/docs/2.asp
809192
Although the nervous system is very complex, there are only two main types of cells in nerve tissue. The actual nerve cell is the neuron. It is the "conducting" cell that transmits impulses and the structural unit of the nervous system. The other type of cell is neuroglia, or glial, cell. The word "neuroglia" means "nerve glue." These cells are nonconductive and provide a support system for the neurons. They are a special type of "connective tissue" for the nervous system.\nNeurons\n\nNeurons, or nerve cells, carry out the functions of the nervous system by conducting nerve impulses. They are highly specialized and amitotic. This means that if a neuron is destroyed, it cannot be replaced because neurons do not go through mitosis.
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Polio affects the anterior horn cells of the spinal cord and also affects motor neurones in the brain. Limb deformities are caused by atrophy of muscles due to disuse, because of paralysis. Polio does not affect blood cells. Polio drops contain live attenuated polio virus.
30212
In biology, a dendrite is a slender, typically branched projection of a nerve cell, or neuron, which conducts the electrical stimulation received from other cells to and from the cell body, or soma, of the neuron from which it projects. These stimulations arrive through synapses, which are located at various points throughout the dendritic arbor. Dendrites were once believed to merely convey stimulation passively, without action potentials and without activation of voltage-gated ion channels. In such dendrites the voltage change that results from stimulation at a synapse will depend on the passive cable properties of the dendrite. In excitable dendrites, voltage gated ion channels help propagate excitatory synaptic stimulation whether or not an action potential is present in the axon. Additionally, action potentials can propagate back into the dendrites once initiated in the axon in most neurons. This backpropagating action potential is mediated by the activation of voltage-gated ion channels and can interact with synaptic input to alter the synaptic activity.\n\nThe structure and branching of a neuron's dendrites strongly influences how it integrates the input from many other neurons, particularly those that input only weakly. This integration is both "temporal" -- involving the summation of stimuli that arrive in rapid succession -- as well as "spatial" -- entailing the aggregation of excitatory and inhibitory inputs from separate branches or "arbors."\n\nThe term "dendrite" comes from the Greek word dendron, meaning "tree".
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Well , you see adult human neyron , that is barin cells have no capacity to regenrate and develop , so with paraplegia some cells have died and are no longer part of cicuit , the circuit has breaken dwon,  so when u infuse these human embryonic stem cells, these cells like embryonic cells have the capacity to divide , develop , and regenerate the circuits , this was re establishing the network which has been disturbed , reverst back to work.
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"Many nerve cells are of the basic type illustrated above. Some kind of stimulus triggers an electric discharge of the cell which is analogous to the discharge of a capacitor. This produces an electrical pulse on the order of 50-70 millivolts called an action potential. The electrical impulse propagates down the fiber-like extension of the nerve cell (the axon). The speed of transmission depends upon the size of the fiber, but is on the order of tens of meters per second - not the speed of light transmission that occurs with electrical signals on wires. Once the signal reaches the axon terminal bundle, it may be transmitted to a neighboring nerve cell with the action of a chemical neurotransmitter. "\n\ni studied this once when i was in matriculation college. i found this quite useful. hope this will help ya..\n\ngood luck