Electrical Stimulation Part 1 Flashcards
Charge:
loss or gain of electrons, measured in coulombs
Polarity:
cathode (-) anode (+) Attraction/repulsion forces = electric field. Alkaline reactions under the cathode softens underlying tissues.
The medication is (+) what charge should the machine be to drive the medication into the body
(+); like polarities repel each other
Voltage:
driving force that moves electrons, a measure of potential energy
Conductor examples:
water, metal, nerves; anything that helps the electrons along their way
Insulator examples:
rubber, plastic, fat; anything that inhibits the transmission
Properties of electrically excitable cell
resting membrane potential (RMP) -70mv usually, Action Potential, Propagation of an Action Potential (movement of the action potential along the nerve)
The cell membrane is more permeable to _____ in comparison with _____________ and negatively-charged proteins (anions).
potassium (K+), sodium (Na+)
An electrical potential is generated across the cell membrane due to the higher concentrations of K+ and anions on the ____ of the cell relative to the concentration of Na+ on the ____
inside, outside
A ____ charge is produced within the cell and a positive charge develops on the outside of the cell as the ____ charged K+ diffuses from the cell
negative, positive
RMP is ____mV to ____mV for excitable cells
-60, -90
RMP is maintained by:
an active sodium potassium pump that takes in K+ and extrudes Na+
A stimulus causes the cell membrane to become more ____ to ___ ions
permeable, Na+
An action potential is generated when the influx of ____ causes a reduction of RMP which occurs slowly at first. Reduction in the RMP is called _____.
Na+, depolarization
When transmembrane potential reaches a critical threshold level (approximately ____mV), the voltage-sensitive Na+ and K+ channels ___.
-55, open widely
Permeability to Na+ increases _____, whereas the permeability to K+ increases _____.
rapidly, slowly
During depolarization, transmembrane potential might rise as high as ____mV. A positive charge is generated inside the cell and a negative charge outside is produced, as a result of the flow of ions.
+35
The ___ channels are fully open about the time the ___ are closed and ___rushes rapidly out of the cell, making the transmembrane potential progressively more negative. This process is repolarization.
K+, Na+, K+
The ____ channels remain open long enough to repolarize the membrane (_________mv <RMP). This is called hyperpolarization.
K+, 10-20
The ____ channels close and passive diffusion of the ions ____ returns the RMP to its initial level.
K+, rapidly
Opening of the Na+ and K+ channels and voltage changes that produce a AP at one segment of the membrane triggers successive depolarization in adjacent regions of the ____, _____, or ____
nerve, muscle, membrane
AP movement occurs along the ____ of the nerve or muscle cell
surface
Movement of the AP along an unmyelinated nerve is generated via sequential depolarization (____) along neighboring sites in the nerve membrane.
eddy currents
Speed of conduction in ____ diameter fibers is ____ because of the greater internal resistance in the small fibers.
small, slow
In myelinated nerve fibers, ______ conduction occurs at discrete junctures (_______) in the myelin sheath which surrounds the nerve
salutatory, nodes of Ranvier
What is the sequence of nerve conduction
- Conduction of an action potential. An action potential is generated as Na+ ions flow in at one location along an axon. 2. The depolarization spreads to the neighboring region of the membrane, initiating an action potential there. 3. The original region repolarized as K+ ions flow out. 4. The depolarization-repolarization process is repeated as the action potential is propagated down the axon.
Na+ and K+ ion exchange and current flow. The impulse jumps from node to node, conducting nerve impulses at greater rates compared to _____, unmylinated nerve fibers.
smaller
In order to cause the membrane potential to be lowered sufficiently to reach threshold levels the _____ or ____ of the stimulus must be great enough.
amplitude, intensity
Duration of the individual stimulus must be long enouh to produce depolarization of the cell membrane. A duration of less than or equal to ___ms is sufficient to stimulate nerve cell membrane, but is too short to stimulate muscle cell membrane.
1
Rate of rise of the current to the peak intensity must be ____ enough to prevent accommodation, which is the ____ adjustment of the membrane to stimuli to prevent depolarization.
rapid, rapid
____ wave delivers instantaneous rise
square
Rheobase:
intensity of the current, having a long duration stimulus, required to produce a minimum muscle contraction
Chronaxie:
the pulse duration of the stimulus at twice the rheobase intensity. Chronaxie of a denervated muscle is >1 msec
What pulse duration can depolarize sensory nerves
very short pulse durations <0.05msec
What pulse duration can depolarize motor nerves
longer pulse durations <1 msec
What pulse duration is required to elicit a response from a denervated muscle
long pulse duration >10 msec with high intensities
Nerve conduction velocity and EMG have rendered __________________ virtually obsolete
strength-duration testing
motor point:
an area of greatest excitability on the skin surface in which a small amount of current generates a muscle response
In innervated muscle, the motor point is located ___ or ___ where the motor nerve enters the muscle, usually over the ___________.
at, near, muscle belly
In denervated muscle, the area of greatest excitability is located _____ the muscle _____toward the insertion
over, distally
A brief muscle twitch or muscle contraction requires a ______ with each stimulus
low frequency pulse (1-10 pulses/sec)
Fusing the number of individual muscle twitches to a point where the individual twitches are not discernible results in a _______; increasing the number of stimuli (frequency) progressively.
tetanic contraction
Tetany:
the involuntary contraction of muscles, which may be caused by disease or other conditions that increase the action potential frequency
Muscle cramps that are caused by the disease tetanus are not classified as tetany; rather, they are due to:
a blocking of the inhibition to the neurons that supply muscles
Denervated muscle produces a ____ response
asynchronous or worm-like (vermicular)
Electrical current:
the movement of electrons through a conducting medium
voltage:
the force that drives electrons through the conductive medium
Resistance:
is the property of a medium which opposes the flow of electrons. A substance having a high resistance (e.g., rubber) is an insulator and a substance having a low resistance (e.g., metal) is a conductor
Ohm’ law expresses the relationship between ____, ____, and _____.
amperage, voltage, resistance
The current is directly proportional to the ____ and inversely proportional to the ____.
voltage, resistance
The inverse of resistance is called ____
conductance
What is Ohm’s Law equation:
I(amps) = V(volts) / R(resistance)
When resistance increases, current _____
decreases
edema control:
high volt
A circuit of 100 volts passes through a tissue with 5 ohms of impedance. How many amps of current are there?
100 V/5 ohms = 20A
Alternating current:
uninterrupted bidirectional flow of electrons, must change direction at least once per second
Pulsed current:
unidirectional/bidirectional flow of electrons that periodically ceases for short time period
Electrochemical effects:
Na+ to cathode (forms NaOH), Cl- to anode (forms HCl) – both combine with water
Electrothermal effects
Heat is a product of kinetic energy of molecules secondary to friction and vibration
Tissue changes may occur with __; minimal concern with __ or pulsed current
DC, AC
What is depolarized first nerves or muscles? At what mV?
nerves are depolarized first (-70mV), then muscles (-90mV)
Levels of stimulation can be ___, ___, and ____
sensory, motor, noxious
Russian current (burst modulation):
variation of AC used for strengthening muscles
What is High-Volt Pulsed Current (HVPC)? What is it used for?
continuous, reciprocating, or surge (monophasic). Used for pain modulation, tissue repair, wound healing.
What is Interferential Current (IFC)? What is it used for?
Quadripolar or bipolar set-ups available on most devices. Used primarily for pain modulation.
What is low-intensity DC (microcurrent)? What is it used for?
It does not stimulate sensory/motor nerves. Used for tissue repair, wound healing
What is symmetrical/asymmetrical biphasic PC?
Used for muscle stimulation & pain modulation. Little to no difference in effectiveness for muscle stimulation using symmetrical biphasic PC vs. Russian.
