10-17a Introduction to Electrotherapy II Flashcards
DC is always flows from
positive to negative
Define AC
uninterrupted bidirectional flow of charged particles
no net change in polarity at either electrode = no chemical effects = zero net current flow
What are the descriptive characteristics of AC?
biphasic
symmetrical (or asymmetrical): same shape on top and bottom
balanced (or unbalanced): top as big as bottom
varied shapes: largely sine and rectangular
What are the characteristics of pulsed current?
mono (only on top) or biphasic pulses
symmetrical (or asymmetrical): same shape on top and bottom
balanced (or unbalanced): top as big as bottom
varied shapes: rectangular, twin peak
Define pulsed current
interrupted uni or bidirectional flow of charged particles
interpulse interval/stop in current
uni or bidirectional flow of charged particles
How long does direct current have to last for?
at least 1 second
What is burst modulated AC current?
AC current with an interpulse interval
What is phase duration
time elapsed from beginning to end of one phase
What is pulse duration?
time elapsed from beginning to end of all phases
What is peak current?
The amplitude of each phase
How can AC cause an ion response around the nerve membrane
migration of negative particles and ions to the surface of the positively charged electrode to change polarity
How can electrodes cause an AP?
if the amplitude and duration of the current is sufficient enough to change the polarity of negative 70
What is capacitance?
The property of a system of conductors and insulators to store charge
How is the cell membrane similar to a capacitor?
phospholipid bilayer partially acts as a resistor by blocking flow of charged ions from moving in and out of the cell
also acts as a capacitor since the cell is more negative intracellularly and positive extracellulary = stores energy by having a different voltage on either side to cause a change in polarity > depolarization
What is the membrane time constant?
membrane Resistance * membrane capacitance
different n. have diff time constants due to diff resistances (larger diameter, less resistance)
some n. are easily excited & some are less easily excited
What is a pulse charge? What is it important for?
area under both positive and negative phases
amps times micro seconds
important for det. excitation of tissue
what is phase charge?
area under half of the phase
Amps times micro seconds
can two pulses w diff amplitudes and durations have the same pulse/phase charge?
yes
What two factors affect tissue excitation?
pulse charge/phase charge and duration
What is the relationship between pulse duration and excitability
the longer the pulse duration, the less intensity (pulse amplitude (mA)) required to excite it
Which neurons are the largest? What do they innervate? What is its level of resistance and excitability?
alpha motor neurons (m. tendons, m.spindles)
largest diameter, lowest internal resistance, most easily excitable
Which neurons are the second largest? What do they innervate? What is its level of resistance and excitability?
beta motor n. (sensory n.) medium resistance and medium excitability
Which neurons are the smallest? What do they innervate? What is its level of resistance and excitability?
Gamma n. (pain n.), highest resistance and lowest excitability
What is the relationship between n. size and excitability?
larger the n., less internal resistance, shorter durations and smaller intensity to become stimulated
