Is the cellular membrane potential positive or negative?
negative, until an action potential occurs
Define refractory period:
Period immediately after a nerve impulse where another impulse cannot be generated; absolute period - none can occur; relative refractory period - a higher than normal stimulus can trigger an impulse
What is salutory / jumping conduction?
On a myelinated nerve the impulse jumps between gaps (nodes of ranvier) making it faster and more efficient
avg conduction velocity for myelinated and unmyelinated?
myelinated ~130 m/s vs unmyelinated ~.5 m/s
What is an ion:
an atom or a group of atom that has a net electrical charge
What is ionization:
process of changing the electrically neutral states of an atom
What is an electrical current?
Atoms with valence shells that are almost full relate to conductivity how?
These are stable and are called insulators which impedes electron movement such as apidose tissue
Atoms with valence shells that only have one or two electrons relate to conductivity how?
These readily relenquish their atoms and are conductors which readily permit electron movement, such as metal
Clinically therapeutic intensities should not exceed what amperage?
What is electromotive force?
1 volt is the electromotive force required to move 1 amp of current through a resistance of 1 ohm
What role does voltage play in nerve cell membrane depolarization?
An adequate number of electrons must be forced to move through conductive tissues.
How does Ohm's law express the relationship between current, voltage, and resistance?
V=IR; when resistance increases, current decreases; when resistance decreases, current increases; when voltage decreases, current decreases; when voltage increases, current increases; when voltage is zero, current is zeo
what properties of a material tend to make it resist electrical currents?
conductors have low resistance, whereas insulators have high resistance. The actual resistance of a material is determined by the formula R(resistance) = P (resistivity = length of material / cross section)
Greater cross sectional effects resistance how?
Increased temperature changes resistance and conductivity how?
decreased resistance and increased conductivity
If the resistor is longer what happens to resistance?
it is increased
Factors that increase skin impedance?
cooler skin temperature, electrode type/surface factors, hair and old present, increased skin dryness, increased skin thickness
Factors that decrease skin impedance?
increasing electrode surface, removing excess hair, warming skin, washing skin
What criteria is used to describe direct current?
DC is flow of electrons in one direction for >1 second. Flow is unidirectional, polarity is constant, current produces a twitch response only at the time of make
Direct currents produce polar effects. what polar effects produced by the anode (positive)?
hyperpolarizes nerve fibers, repels bases, hardens tissues, stops hemorrhage, sedates and calms, reduces pain in acute situations
Direct currents produce polar effects. what polar effects produced by the cathode (negative)?
depolarizes nerve fibers, attracts bases, softens tissues, increases hemorrhage, stimulates, reduces pain in chronic situations
What are the criteria used to describe alternating current (AC)?
The magnitude of flow of electrons changes, the direction of flow reverses, there are no polar effects, constantly flucuates
List the typical frequencies (change of currents, if applicable) used in therapeutic applications)
Frequency (Hz): 0 = direct current, 0-1000 = low frequency, 1000-100000 = medium frequency, 100000+ = high frequency
Does medium-frequency stimulation differ from low frequency stimulation in terms of skin resistance (capacitive impedance)
yes, capacitance impedance decreases as the frequency increases
Describe key attributes of interferential currents (IFC):
- two separate force generators that vary in relation to one another in amplitude and/or frequency, the difference of the two frequencies bcreases a beat frequency which is felt by the patient
What is the frequency for a twitch contraction?
What is the frequency for a tetantic contraction?
What is the frequency for a nonfatiguing tetanic contraction?
What is the frequency for a fatiguing tetanic contraction?