Physiologically Induced Muscle Contraction

Question 1

orthodromic

Answer 1

normal movement down a nerve, AP firing from cell body down axon to terminal

Question 2

antidromic

Answer 2

electrical stimulation causes APs to propagate along peripheral nerve in both directions from stimulus
this creates non physiological loops

Question 3

size principle of motor neurons, physiologic

Answer 3

smaller motor neurons require less synaptic current to produce an AP and will be activated first
in a muscle contraction, the small, 1A fibers will be activated first, then 2A, then the largest 2X
SMALL to LARGE

Question 4

size principle in estim

Answer 4

because estim is activating nerve fibers antidromically, it will activate those with the least resistance first
the largest nerves have the lowest internal resistance and will be activated before smaller ones
LARGE to SMALL

Question 5

using the size principle, why does NMES have a rest time?

Answer 5

estim recruits hast fatiguable fibers first, so they need a rest time to repolarize

Question 6

rate coding

Answer 6

increased rate of motor unit discharge will increase muscle tension and fiber recruitment

Question 7

physiologic discharge rate

Answer 7

30 pps
this is the critical fusion rate to get organized muscle contraction
under this level you will get fasciculations

going over this rate will increase fatigue

Question 8

asynchronous recruitments

Answer 8

smooth switching between active and inactive units to avoid fatigue in fibers
this means discharge frequencies are not the same in all motor units to create functional movement

Question 9

synchronous recruitment

Answer 9

the same motor units are continually activated based on level of current and fibers’ resistance levels
estim does this and activates fatiguable fibers first, increasing fatigue levels

Question 10

how does electrode placement affect recruitment?

Answer 10

size principle is often overridden by electrode placement, as it is easier for current to activate fibers that are closest
smaller fibers that are in closer proximity will be activated before larger fibers that are farther away

Question 11

how to get smooth contraction with estim

Answer 11

ramping: offset lack of rate coding
frequency: 30 pps or greater for tetanic contraction
on/off: allow rest for recruited fibers to offset synchronous activation effect
electrode placement: allow specificity of recruitment

Question 12

optimal contraction with estim

Answer 12

combine estim with voluntary contraction
voluntary contraction recruits slow fibers and estim recruits fast fibers