Muscle and Nerve Excitability

Question 1

What is normal resting membrane potential

Answer 1

-60-90 millivolts with the inside more negative than the outside due to an unequal ion distribution

Question 2

how is an action potential generated

Answer 2

post stimulus the cell membrane changes its permeability and Na+ rushes in causing a reduction in negative charge (depolarization) –> if critical level is reached an action potential results

Question 3

what does the ability of cathodes attracting positive ions cause

Answer 3

the area near the membrane of nerve becomes more defect in negative charge, making it easier to generate AP

Question 4

what does the ability of an anode attracting negative ions (anions) cause

Answer 4

increases negative charge at the cell membrane making depolarization and AP more difficult

Question 5

what does a positive electrode require to depolarize and cause an action potnetial

Answer 5

slightly greater current intensity

Question 6

in what direction do electrically induced action potentials travel

Answer 6

both

Question 7

what orthodromic conduction

Answer 7

conduction in the normal physiological direction

Question 8

what is antidromic conduction

Answer 8

conduction in the opposite direction of normal physiologic directoin

Question 9

what factors influence muscle force

Answer 9

frequency of rate coding
number of fibers activated or recruited
resting length of the muscle

Question 10

what are the stimulus parameters for the activation of excitable tissue

Answer 10

-sufficient phase charge (amplitude and direction)
-sufficient rise time to avoid accommodation –> rise time must be <60 milliseconds
-polarity

Question 11

what polarity is more effective at activating excitable tissue

Answer 11

negative cathode

Question 12

what are S-D curves

Answer 12

graphs of the amplitude needed for any given duration to cause and AP in a specific nerve

Question 13

what are S-D used for

Answer 13

historically they are sued for testing the integrity of the muscle

Question 14

when is it easier to discern between sensory and motor responses in S-D curves

Answer 14

at shorter durations

Question 15

what is reobase

Answer 15

the amount of current amplitude required to causes minimal contraction when an infinitely long stimulus duration is applied (infinite duration is defined as 100 to 300 microseconds or when the curve flattens out)

Question 16

what is chronaxy

Answer 16

the time required for a current of twice the rebase to cause minimal contraction

Question 17

what does denervated muscle tend to not respond to

Answer 17

anything less than 1 millisecond

Question 18

what would happen if fibers were recruited by size

Answer 18

motor fibers would be recruited first followed by sensory and pain

Question 19

how are a fibers recruited in response to electrical stimulation

Answer 19

sensory first, followed by motor then pain because sensory is located closer to the stimulation

Question 20

what is theory 1 of muscle strengthening with NMES

Answer 20

muscle overload - e stim stresses the muscle above its typical contraction capabilities (not likely this mecahnisms because intensity needed to uncomfortable)

Question 21

what is theory 2 of muscle strengthening with NMES

Answer 21

differnet recruitment pattern - e stim selectively recruites type II fibers (larger diameter) first, type II may not be recruited with voluntary contractions with certain injuries with voluntary contractions with certain injuries, voluntary contractions recruit type I fibers first,

Question 22

what do type II fibers fatigue so fast

Answer 22

e stim causes greater fatigue than voluntary muscle contractions and e stimulation causes synchronous firing which fatigues muscles faster

Question 23

what is the recruitment order for voluntary contractions and e time induced contractions

Answer 23

type II first, because of their large diameter

Question 24

what part of muscle in recruited between voluntary and e stimulation induced contractions

Answer 24

the fibers attached to the motor axon that is activated are recruited

Question 25

how does the motor unit fire in voluntary and e stimulation induced contractiosn

Answer 25

asynchronous