Electrical Agents Flashcards
(58 cards)
Resting membrane potential - cell membrane is more permeable to
potassium compared to sodium and negatively charged proteins (anions)
Electrical potential is generated across the cell membrane due to
higher concentration of K and anions on the inside relative to concentration of Na on outside
Resting membrane potential is maintained by
active Na/K pump that takes in K and extrudes Na
Action potential - a stimulus causes the cell membrane to become
more permeable to Na ions
An action potential is generated when
the influx of Na causes a reduction in resting membrane potential which occurs slowly at first
this reduction in membrane potential is called depolarization
During depolarization, transmembrane potential is where
can be as high as+35 mV
a positive charge is generated inside the cell and a negative charge outside the cell is produced
Repolarization - what happens
K channels are fully open at about the time that the Na are closed and K rushes out of the cell making the membrane potential more negative
Hyperpolarization - what happens
K channels stay open long enough to repolarize the membrane
Strength-duration curve: Rheobase
the intensity of the current with a long duration stimulus required to produce a minimum muscle contraction
Strength duration curve: Chronaxie
the pulse duration of the stimulus at twice the rheobase intensity
Motor point
An area of greatest excitability on the skin surface in which a small amount of current generates a muscle response
In an innervated muscle, the motor point is located
at or near where the motor nerve enters the muscle, usually over the mm belly
In denervated muscle, the motor point is located
over the muscle distally toward the insertion
The current has what relationship with voltage
directly related
The current has what relationship with resistance
inverse relationship
Inverse of resistance is called
conductance
Monophasic wave forms
Direct or galvanic
A unidirectional flow of charged particles
Current flow in one direction for a finite period
All either above or below baseline
Biphasic wave forms
alternating current
a bidirectional flow of charged particles
1/2 the cycle above baseline, 1/2 below
Polyphasic wave forms
biphasic current modified to produce three or more phases in a single pulse
medium freq and can be Russian or IFC
Current modulation - Surge mode
a gradual increase and decrease in the current intensity over a finite period of time
Current modulation - Ramped mode
a time period with a gradual rise of the current intensity which is maintained at a selected level for a given period or time followed by a gradual or abrupt decline in intensity
Contraindications to Estim
Anywhere that pt has pacemaker or electronic device
Over or in area of carotid sinus, thromb, eyes, thoracic area, phrenic, low back with preg
Presence of active bleeding or infection
Superficial metal implants
Pharyngeal/Laryngeal mm
Guidelines - Electrode size
Two leads are required to complete the current circuit
One active and one inactive (or dispersive)
Guidelines - current density
relative to electrode size
A given current intensity passing through the smaller active electrode produces high current density and thus a strong stimulus while same current is perceived as less intensive under a larger dispersive electrode
