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NMES denervated
NMES denervated
53
Anatomy
Graduate
02/28/2012

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Term
what is the cause of wallerian degeneration
Definition
peripheral nerve damage
Term
what is the result of wallerian degeneration
Definition
disruption of axons cuts off the motor units that were served
Term
what are the 2 ways in which axons are cut off
Definition
electrically and chemically
Term
how are axons electrically cut off (what is lost)?
Definition
action potentials can no longer flow across the degenerated part
Term
how are axons chemically cut off (what is lost)?
Definition
axoplasmic/neuroplasmic flow of substance to/from cell body to/from axon is cut off
Term
what physiologic changes occur in the proximal portion of a damaged nerve
Definition
changes in metabolism; degeneration; regrowth
Term
what does the proximal portion of the damaged nerve do to assist regrowth
Definition
sends axoplasmic flow to try to regrow
Term
what physiologic changes occur in the distal portion of a damaged nerve
Definition
axon dies and disorganizes; macrophages move in and breakdown/resorb; myelin sheath is phagocytized; neural tube with connective tissue remains
Term
what part of the damaged nerve will serve for regrowth in the future
Definition
neural tube
Term
what do schwann cells do to help repair from nerve damage
Definition
proliferate and line up along nerve route to provide assistance for where the nerve will regrow
Term
how long does it take degeneration to become evident following damage
Definition
7-10 days
Term
what things affect a damaged nerve's ability to regrow?
Definition
depth of damage, formation of scar tissue, distance between 2 cut nerve ends
Term
how does muscle fiber size change from disuse
Definition
decreased fiber size from disuse
Term
how do sarcomeres change from disuse
Definition
become smaller in diameter because muscle fibers are smaller, but still remain
Term
how do contractile proteins change from disuse
Definition
decreased contractile proteins
Term
are type I or II fibers lost from disuse
Definition
both are lost, but you lose Type I fibers faster than type II
Term
what determines the severity fo changes from disuse
Definition
duration of inactivity
Term
is disuse or denervation worse?
Definition
denervation is worse. You can usually reverse disuse as long as you don't wait too late
Term
how do sarcomeres change from denervation
Definition
you lose them: you lose the protein and the structure of sarcomeres
Term
what causes atrophy due to denervation
Definition
loss of sarcomeres
Term
what determines the speed of sarcomere loss
Definition
the faster the metabolism, the faster the loss
Term
do humans have a very fast metabolism?
Definition
not compared to other animals
Term
what is the result of continued degeneration of a muscle
Definition
fibrosis = no viable muscle to regenerate
Term
how long does it take for fibrosis to occur?
Definition
2-3 years following damage
Term
how fast does regeneration occur?
Definition
1 inch/month
Term
how does a denervated muscle's sensitivity to acetylcholine change?
Definition
entire membrane of the muscle fiber (not just motor end plate) becomes sensitive to acetylcholine
Term
what is the motor point
Definition
point of the muscle that attaches to the nerve. Most sensitive part of the muscle
Term
where is the motor point
Definition
usually at the center of the muscle body
Term
where is the motor point in denervated muscle
Definition
moves toward the tendon
Term
what parts of the muscle become more tender following denervation
Definition
musculotendinous areas become more tender
Term
how does the resting potential of a denervated muscle change and why
Definition
becomes less negative to make it easier to reach threshold so that muscle fiber can fire more easily
Term
how does the muscle fiber membrane change with denervation and why?
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
Term
how does the muscle endplate adapt to denervation
Definition
develops pacemaker qualities so that the muscle can contract at its own rate
Term
what are the 3 muscle denervation cellular changes that help the muscle fiber survive
Definition
acetylcholine hypersensitivity, resting potential becomes less negative, endplate develops pacemaker qualities
Term
what do the cellular survival mechanisms following muscle denervation end up causing
Definition
fibrillation
Term
what is fibrillation
Definition
sponatenous, uncoordinated contractions of fibers
Term
how does denervated muscle respond to short duration pulses (shorter than 600us)
Definition
decreased or no response
Term
what type of duration pulses does denervated muscle respond to
Definition
duration of millisecons
Term
how does a denervated muscle react to electrical stimulation with a long pulse
Definition
sluggish contraction
Term
at what frequency do you get tetanus in denervated muscle
Definition
15-25pps
Term
what is the frequency range to obtain a tetanic motor response in intact muscle?
Definition
21-50pps
Term
why does a lower frequency cause a tetanic contraction in a denervated muscle
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
Term
define rheobase
Definition
minimal amplitude of current required to elicit a minimal contraction (first visible twitch)
Term
define chronaxie
Definition
minimal duration of 2x the rheobase that elicits a minimal contraction
Term
functional use of rheobase and chronaxie
Definition
use them to follow the amount of degeneration and see if you're starting to regenerate
Term
what is nodal collateral sprouting
Definition
a close intramuscular nerve sprouts axons from its Nodes of Ranvier to re-innervate the denervated muscle
Term
how do nearby nerves know that a muscle has been denervated
Definition
muscle fiber sends out a help signal through its contractions
Term
what is terminal collaterals prouting
Definition
a close intramuscular nerve sprouts axons from its axon terminal to re-innervate the denervated muscle
Term
what are the benefits of using electrical stimulation to contract a denervated muscle
Definition
limit edema, and venous stasis, delay fibrosis, shorten recovery time
Term
what is the rational against electrically stimulating a denervated muscle
Definition
may disrupt nerve regeneration and may further traumatize a sensitive muscle
Term
how can stimulation disrupt nerve regeneration in a denervated muscle
Definition
stops the process of the muscle's fibrillation
Term
what is the time/effort/cost of muscle stimulation to denervated muscles
Definition
high: have to do it 3-4 times a day, also very uncomfortable on the skin because duration is so long
Term
what type of current is used to electrically simulate denervated muscle?
Definition
interrupted DC, sinusoidal low frequency AC, expontentially progressive current
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