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What is an ion?
when protons and electrons are not equal
What do atoms contain?
- nucleus (protons (+) and neutrons)
- electrons (surround nucleus (-) )
What type of electrons are loosely attached to atoms and can move?
What is matter composed of?
What is a charge?
- property of matter
- either neutral, positively charged, or negatively charged
- measured in Coulombs (C)
In therapy, what do we measure charge in?
What is the mvmt of charged particles (electrons or ions) through a conductor in response to an applied electric field?
What is polarity?
- having 2 oppositely charged conductors
- (+) is called the anode
- (-) is called the cathode
in a conductor, free electrons flow from an area of excess electrons (-) pole to an area deficient in electrons (+) pole
Is an anode positive or negative?
Is a cathode positive or negative?
What is current measured in?
amps (ampere) (A)
in therapy, its measured in milliamps (mA) or microamps (uA)
What is an ampere?
rate at which the electrical current flows (flow rate)
At 0-1mA, what is the tissue reponse?
At what mA do we perform e-stim in therapy and what is the tissue response?
At what mA does painful electric shock begin?
At 100-200mA, what is the tissue response?
cardiac fibrillation/respiratory arrest
What occurs at 200+mA?
rapid burning/destruction of tissue
What is the electrical force capable of moving charged particles between 2 points?
also known as potential difference
What is resistance (R)?
ease or difficulty of current moving through a substance
What is a material that offers little opposition to current flow?
materials composed of very reactive atoms with freely moving and loosely bound electrons in the outer orbit
What are good conductors in the human bosy?
nerves and muscles
moves easily through
What is a material that resists current flow?
electrons are tightly bound in the outer orbit
What are good insulators in the human body?
What is impedance (Z)?
opposition of electrical currents to flow of alternating current
What is impedance (Z) measured in?
With injury, increased impedance is caused with what conditions?
with increased impedance, it is harder to get current through
With injury, impedance is decreased with what conditions?
What is Ohms law?
- voltage=current x resistance
- current- rate of flow measured in amps
- voltage- strength of flow
- resistance- ease or difficulty of flow
What are the three forms of current?
- direct current (DC)
- alternating current (AC)
- pulsatile current (pulsed)
What is another name for direct current?
- continuous unidirectional
What type of current is a continuous unidirectional flow of charged particles with a duration of at least one second?
- one electrode is always positive, other is always negative
- direction of flow is determined by polarity selection
What type of current can induce chemical reactions in the body and residual changes under the electrodes and in tissues?
What 2 things can only direct current do?
- iontophoresis (uses continuous DC)
- stimulate denervated muscle (uses pulsed DC)
What type of current has an uninterrupted bidirectional flow of charged particles changing direction at least once a second?
alternating current (AC)
- electrode is positive then negative as it reverses
- no build up of charge like dc
What is another name for alternating current?
- uninterrupted bidirectional flow
What is the inverse relationship in alternating current?
between cycle duration and frequency
if cycle duration increases, frequency decreases - vis versa
What is current thats delivered discontinuously in a series of pulses separated by periods when no current flows?
most widely used clinically and most commonly generated
can be either unidirectional (hivolt) or bidirectional (TENS, russian)
Under what conditions does current flow?
- source of energy creating a diference in electrical potential
- conducting pathway (skin has a high impedance/resistance)
Which direction does current flow?
- from positive anode to negative cathode
- in the body, current = flow of ions
- chemical reaction soccur at the interface between the electrode and the tissue during the transfer of charge
What is current density?
determined by the amount of current applied and size of the area of application
important factor in determining tissue response to stimulation
the greater the current density, the greater the tissue response
What does current density depend on?
electrode size - if electrode size decreases, then the electrode contact area decreases and current (or charge density) increases
excessive current or charge density can lead to tissue damage or surface burns (hot spots)
What is a waveform?
visual representation of the current flow (shape, direction, amplitude, and duration)
main variables are amplitude, duration, and rise time
What is the magnitude of current or voltage?
What is frequency?
- number of cycles or pulses per second
- measured in hertz (Hz) or pulses per second (pps)
What 2 things can you increase to increase the ability to excite nervous tissue?
What is monophasic?
- only one phase (from start to finish)
- can be either positive or negative
- phase describes the flow of charges in direction
What is biphasic?
- bidirectional with 2 phases
- both positive and negative, bidirectional
- symmetrical biphasic (shape)
- balanced: charge of the phases are equal
- unbalanced: charge of the phases are not equal and get a net (+) or (-)
What are asymmetrical biphasics?
- shapes are asymmetrical
What is a polyphasic waveform>
- 3 or more phases
- bursts- groups together a finite series of pulses and delivers them as a single charge
- (synonyms-packet, envelope)