electrical currents Flashcards
what is electrical flow?
the flow of charged particles
what does an electrical circuit consist of?
-battery
-2 electrodes
-wires
-electrolytic solution
where do positive ions flow towards?
the cathode
where do negative ions flow toward?
- the anode
what is voltage?
the difference in electrical potential between 2 points -it is the force that pushes electricity through wire
what are the 3 steps of current?
-direct
-alternating
-pulsed
what is a direct current?
-flow of electrons in one direction only
-rarely used now in electrotherapy
-higher risk of burn
what are alternating current (AC)?
-continuous flow of charged particles in 2 directions
what is a pulsed current?
an electrical current that is delivered through pulses
-most common current used in electrotherapy
what are the types of pulsed currents?
-biphasic symmetrical PC
-biphasic assymmetrical PC
what is he frequency / rate of currents?
-number of pulses or cycles delivered per unit time
-measured in pulses per second or Hz
-low freq eg TENS / NMES - 0-1000Hz
what is a pulse duration?
the length of time the pulse lasts
what is the peak amplitude of a current?
the maximum amplitude per phase
what is the amplitude of the current?
-intensity or magnitude of current - milliamps
-this is what the patient feels
what is the ramp time?
- the time taken for the amplitude to reach a peak
what is ramp down time?
-the time taken for amplitude to return to 0
define ohms law
voltage = current x resistance
V=IR
what is the major resistance to current in electrotherapy and why does it vary?
the skin - acts as a capacitor
-skin resistance can vary due to thickness, moistness, blood supply
define accommodation in physiology
-occurs during generation of AP
-refers to the rate of rise of a single electrical pulse in response to a stimulus
-if the rate is very flow, it will not provoke a nerve impulse
what is adaption in physiology
an initial burst of impulses on stimulation and then the discharge rate falls greatly or may cease altogether
-occurs in most sensory types
why is adaption important clinically?
the patient will feel a decrease in the intensity of the current after a few minutes
what is a modulating current?
currents with sequential variations in the amplitude or pulse or frequency
what does the order of nerve and muscle recruitment depend on?
type and size of nerve fibre
what are the important nerve fibre types we need to know about in electrotherapy?
A alpha - motor to skeletal muscle
A beta- sensory touch and pressure
A gamma - motor to intramural fibres of muscle spindles
-A delta - sensory pain
C fibres - sensory pain
what are general indications for use of electrical currents?
-pain control
-muscle stimulation
-iontophoresis-drug delivery
-enhance tissue healing
what are electrodes used for in electrotherapy?
-used to conduct the current to the patients body
