Unit II Flashcards
(74 cards)
What are the key physiological concepts of excitable cell membranes?
- resting membrane potential
- semi-permeable membrane
- depolarization
- propagation of action potential
- volume conduction through electrolytes
What are the benefits of myelination?
- increases speed of conduction
- saves space
- saves energy
What are the stimulus amplitude values for nerve and muscle? Pulse duration?
nerve: amplitude = -70mV; pulse duration = 1 msec
muscle: amplitude = -90mV; pulse duration = 35 msec
Accommodation
decreased excitability with slow “rate of rise” (ideal < 60 microseconds); generally want to avoid accommodation with rapid “rate of rise”
Law of Dubois Reymond
- stimulus amplitude must be sufficiently high to cause depolarization
- the rate of change of voltage must be sufficiently rapid to avoid accommodation
- duration of stimulus must be long enough to overcome latent period and allow action potential and recovery to occur
Critical Fusion Frequency (i.e. tetany)
Range: 15 to 40 pps
High Frequency Fatigue
> 50 Hz (occurs rapidly, versus physiological fatigue which occurs slowly, with long recovery period)
Propagation failure - occurs at branch points where motor nerve divides to innervate individual mm fibers
*Review slides from lecture
Cation
positive ion has lost one or more electrons; cation = cathode (negative pole)
Anion
negative ion has gained one or more electrons; anion = anode (positive pole)
To have current flow, must have:
- source of free electrons (+) ions
- material that allows electrons to flow (conductor)
- electromotive force (EMF) that “pushes” electrons
What are the three ways to measure amplitude in AC?
- peak
- peak-to-peak
- root mean square = .707 x peak value
What are the three ways to measure amplitude in AC?
- peak
- peak-to-peak
- root mean square = .707 x peak value
Impedence
resistance - opposes current flow; capacitance - ability of material to store electrical energy by means of electrostatic field; & inductance - ability to store charge by means of electromagnetic field
AC: impedance = res + cap + ind
What are the considerations for stimulator output?
- wave form
- amplitude
- duration
- duty cycle
- modulation (amplitude, duration, frequency, “rise time”)
What are the two types of clinically used electrical stimulation?
- Pulsed Current (HVPC and TENS)
- Burst Modulated Alternating Current (Russian and IFC)
What are the two types of wave forms?
- DC (aka galvanic): continuous and pulsed
- AC (aka faradic)
What are the four components of stimulator hardware?
- power source (AC or DC)
- oscillator circuit
- output amplifier
- modulating circuit
When using a device that uses DC, where should the electrodes be placed?
the cathode (-) should be placed directly over the motor point because it allows for a greater concentration of electrons
Pfleuger’s Law
CCC > ACC > AOC > COC
How are patient’s often injured using e-stim?
In the electrodes commonly used today, the karaya gum and carbon lattice have a tendency to wear off after a few uses, resulting in more concentration and electrical burns of the patient
Electrode Size and Placement
both relate to current density; larger electrodes disperse charge, while smaller electrodes concentrate charge
placement goals: parallel to longitudinal direction of mm, over the motor point, and close together (increases stim)
How can you decrease impedance?
- mild abrasion
- tissue warming
- hydration
- higher frequency signaling
Skin impedance depends on the _____ ________, NOT the _____ ________
phase duration; pulse frequency
Physiologic Effects of Electrical Current
- 1 mA = threshold for tingling sensation
- 16 mA = can’t release grip on conductor d/t contraction
- 50 mA = pain and possible fainting
- 100 mA to 3 A = ventricular fibrillation
- 6 A = sustained myocardial contraction, temp resp paralysis, burns