Term
| what is the cause of wallerian degeneration |
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Definition
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Term
| what is the result of wallerian degeneration |
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Definition
| disruption of axons cuts off the motor units that were served |
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Term
| what are the 2 ways in which axons are cut off |
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Definition
| electrically and chemically |
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Term
| how are axons electrically cut off (what is lost)? |
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Definition
| action potentials can no longer flow across the degenerated part |
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Term
| how are axons chemically cut off (what is lost)? |
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Definition
| axoplasmic/neuroplasmic flow of substance to/from cell body to/from axon is cut off |
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Term
| what physiologic changes occur in the proximal portion of a damaged nerve |
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Definition
| changes in metabolism; degeneration; regrowth |
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Term
| what does the proximal portion of the damaged nerve do to assist regrowth |
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Definition
| sends axoplasmic flow to try to regrow |
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Term
| what physiologic changes occur in the distal portion of a damaged nerve |
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Definition
| axon dies and disorganizes; macrophages move in and breakdown/resorb; myelin sheath is phagocytized; neural tube with connective tissue remains |
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Term
| what part of the damaged nerve will serve for regrowth in the future |
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Definition
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Term
| what do schwann cells do to help repair from nerve damage |
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Definition
| proliferate and line up along nerve route to provide assistance for where the nerve will regrow |
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Term
| how long does it take degeneration to become evident following damage |
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Definition
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Term
| what things affect a damaged nerve's ability to regrow? |
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Definition
| depth of damage, formation of scar tissue, distance between 2 cut nerve ends |
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Term
| how does muscle fiber size change from disuse |
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Definition
| decreased fiber size from disuse |
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Term
| how do sarcomeres change from disuse |
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Definition
| become smaller in diameter because muscle fibers are smaller, but still remain |
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Term
| how do contractile proteins change from disuse |
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Definition
| decreased contractile proteins |
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Term
| are type I or II fibers lost from disuse |
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Definition
| both are lost, but you lose Type I fibers faster than type II |
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Term
| what determines the severity fo changes from disuse |
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Definition
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Term
| is disuse or denervation worse? |
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Definition
| denervation is worse. You can usually reverse disuse as long as you don't wait too late |
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Term
| how do sarcomeres change from denervation |
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Definition
| you lose them: you lose the protein and the structure of sarcomeres |
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Term
| what causes atrophy due to denervation |
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Definition
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Term
| what determines the speed of sarcomere loss |
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Definition
| the faster the metabolism, the faster the loss |
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Term
| do humans have a very fast metabolism? |
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Definition
| not compared to other animals |
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Term
| what is the result of continued degeneration of a muscle |
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Definition
| fibrosis = no viable muscle to regenerate |
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Term
| how long does it take for fibrosis to occur? |
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Definition
| 2-3 years following damage |
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Term
| how fast does regeneration occur? |
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Definition
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Term
| how does a denervated muscle's sensitivity to acetylcholine change? |
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Definition
| entire membrane of the muscle fiber (not just motor end plate) becomes sensitive to acetylcholine |
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Term
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Definition
| point of the muscle that attaches to the nerve. Most sensitive part of the muscle |
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Term
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Definition
| usually at the center of the muscle body |
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Term
| where is the motor point in denervated muscle |
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Definition
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Term
| what parts of the muscle become more tender following denervation |
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Definition
| musculotendinous areas become more tender |
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Term
| how does the resting potential of a denervated muscle change and why |
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Definition
| becomes less negative to make it easier to reach threshold so that muscle fiber can fire more easily |
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Term
| how does the muscle fiber membrane change with denervation and why? |
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Definition
| muscle fiber membrane increases to make it more difficult to fire off action potentials on the muscle fiber membrane, thereby protecting the muscle from external electrical sitmulation |
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Term
| how does the muscle endplate adapt to denervation |
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Definition
| develops pacemaker qualities so that the muscle can contract at its own rate |
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Term
| what are the 3 muscle denervation cellular changes that help the muscle fiber survive |
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Definition
| acetylcholine hypersensitivity, resting potential becomes less negative, endplate develops pacemaker qualities |
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Term
| what do the cellular survival mechanisms following muscle denervation end up causing |
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Definition
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Term
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Definition
| sponatenous, uncoordinated contractions of fibers |
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Term
| how does denervated muscle respond to short duration pulses (shorter than 600us) |
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Definition
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Term
| what type of duration pulses does denervated muscle respond to |
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Definition
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Term
| how does a denervated muscle react to electrical stimulation with a long pulse |
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Definition
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Term
| at what frequency do you get tetanus in denervated muscle |
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Definition
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Term
| what is the frequency range to obtain a tetanic motor response in intact muscle? |
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Definition
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Term
| why does a lower frequency cause a tetanic contraction in a denervated muscle |
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Definition
| the response is sluggish and is only tetanic because it takes a long time to come on and a long time to turn off. There is no short twitch |
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Term
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Definition
| minimal amplitude of current required to elicit a minimal contraction (first visible twitch) |
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Term
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Definition
| minimal duration of 2x the rheobase that elicits a minimal contraction |
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Term
| functional use of rheobase and chronaxie |
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Definition
| use them to follow the amount of degeneration and see if you're starting to regenerate |
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Term
| what is nodal collateral sprouting |
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Definition
| a close intramuscular nerve sprouts axons from its Nodes of Ranvier to re-innervate the denervated muscle |
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Term
| how do nearby nerves know that a muscle has been denervated |
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Definition
| muscle fiber sends out a help signal through its contractions |
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Term
| what is terminal collaterals prouting |
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Definition
| a close intramuscular nerve sprouts axons from its axon terminal to re-innervate the denervated muscle |
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Term
| what are the benefits of using electrical stimulation to contract a denervated muscle |
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Definition
| limit edema, and venous stasis, delay fibrosis, shorten recovery time |
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Term
| what is the rational against electrically stimulating a denervated muscle |
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Definition
| may disrupt nerve regeneration and may further traumatize a sensitive muscle |
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Term
| how can stimulation disrupt nerve regeneration in a denervated muscle |
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Definition
| stops the process of the muscle's fibrillation |
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Term
| what is the time/effort/cost of muscle stimulation to denervated muscles |
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Definition
| high: have to do it 3-4 times a day, also very uncomfortable on the skin because duration is so long |
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Term
| what type of current is used to electrically simulate denervated muscle? |
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Definition
| interrupted DC, sinusoidal low frequency AC, expontentially progressive current |
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