VCU DPT - Agents (Muscle and Nerve Excitability)

what are the three physiological responses to electrical current

chemical

thermal

physical

is it easier to generate an action potential under a cathode or an anode

cathode

- starting negative and attracting all the positives to it

if estim splits NaCl up, which ion goes to the cathode and which to the anode

Na is +, so it is attracted to negative

- goes to cathode

Cl is -, so it is attracted to positive

- goes to anode

with an anode, it will attract a _________ ion

the resulting reaction is considered to be _________

and the end result of the process is ________, which has a ________ effect on the skin

negative

acidic

sclerotic, hardening

anode attracts ________

acid

AAA

cathode attracts _________

base

CAB

with a cathode, it will attract a ________ ion

the reaction that occurs will be considered __________

the end result of the process is ________, which has a _____ effect on the skin

positive

basic/alkaline

scleroLYTIC, softening

with the cathode....

the pH will __________, the amount of water _______, and protein density _______

increases

increases

decreases

when trying to soften scars, we use direct current and place the ___(anode/cathode)___ over the scar

cathode

energy is not created or destroyed, but exchanged. therefore, some energy is lost in the form of _______

heat

our skin will resist the transcutaenous delivery of current. what does this mean

it faces resistance, and heat will be generated

electrothermal effects of e-stim are dependent on what three things

amount of current flowing

current resistance

duration of delivery

______________ is the resistance of tissue to passage of electrical current flow

electrical impedence

define tissue impedence

it is the resistance a tissue poses while receiving an electrical current

put the following tissues into categories based on high or low impedence

- fat

- fascia

- nerve

- muscle

- bone

high: fat, bone, fascia

low: muscle, nerve

- stuff we try to target!!!

impedance will _________ with edema, ischemia, scarring, denervation

impedance will __________ with open wound and abrasion

increase (higher resistance)

decrease (current goes easier)

oily skin, lotion, make up, body hair, and calloused skin has WHAT effect on impedance

they increase it

what is resting membrane potential (roughly)

-70mV

if you provide a strong enough amplitude of e-stim for long enough, what will happen

nerve depolarizes, and an action potential occurs

does the body act differently to an e-stim depolarization compared to a volitional one

nope

sees action potential, contracts

does e-stim have a direct effect on the nerve or the muscle

nerve

- it depolarizes nerve, which then stimulates muscle

e stim will _________ affect nerve, and ________ affect muscle

(answer choices: indirectly, directly)

directly, indirectly

with suffecient ____________ and ______, an e-stim causes the nerve to depolarize and an action potential to be generated

amplitude

duration

a stimulus must be of suffecient ________ and suffecient __________

strength

amplitude

a stimulus must be of sufficient strength, represented by __________

a stimulus must be be of sufficient duration, represented by ___________

amplitude

pulse duration

describe a subthreshold stimulus, and a suprathreshold stimulus

subthreshold is one where the ampltiude, duration, or both is not strong enough to cause a reaction

suprathreshold is one where the amplitude, duration, or both have far exceeded the minimum needed to cause a stimulus

define the rheobase

the minimum intensity that is capable of eliciting a detectable motor response

what is a double rheobase

rheobase itself is the minimum intensity needed to get a motor response

double rheobase is usually a good estimate to use for intensity, while accounting for skin impedence

define the chroniaxie

the amount of time that is needed to administer the double rheobase intensity, based on strength duration curve

describe, using a strength-duration curve,

1. rheobase

2. double rheobase

3. chronaxie

1. the minimum intensity needed to get motor response

- the lowest intensity on the curve

2. double the rheobase. allows for use to account for skin impendence when giving e-stim

3. this is the point of the duration axis (x-axis) where the double rheobase meets the curve

- double rheobase and chronaxie make a right angle where they meet along the curve

do nerve size and location of electrodes affect S-D curve?

do any other factors impact S-D curve

yes and yes

amplitude (intensity), duration

how does nerve size affect S-D curve

the nerve fibers with greatest diameter, and lowest resistance will depolarize first

the nerve fibers that will depolarize first have ______ diameters and _______ resistance

higher

lower

rank the following nerves based on fiber diameter, large to small

a-beta

a-delta

a-alpha

c

a-alpha

a-beta

a-delta

c

what stimulus does the following nerve fibers transmit:

a-alpha

a-beta

a-delta

c

a-alpha: motor, proprioception

a-beta: touch, pressure

a-delta: pain, temp

c: pain

the fibers located _______ from the electrode will become excited before fibers ________

closer

farther away

why do we feel an e-stim before we see a motor response

because the fibers closest to the electrode are excited before ones farther away

how do we stimulate deeper fibers

seperate the electrodes farther away from each other

what pattern do we see, in terms of depolarizing from first to last

- pain

- sensory

-motor

sensory --> motor --> pain

if the patient is feeling pins and needles (sensory, a-beta) and we want to get a motor response (a-alpha), how do we change:

1. intensity

2. pulse duration

increase BOTH