MCQ Test 1 Flashcards
(62 cards)
1
Q
Current Flow
A
- Ions flow will follow the path of least resistance
- nerves
- muscles
- blood vessels
- current usually does not flow from electrode-to-electrode(the shortest path)
- the path of least resistance is not necessarily the shortest path
2
Q
Ions Flow( Current Flow)
A
- occurs within the nerves
- negative ions flow towards the anode and away from the cathode
- positive ions flow towards the cathode and away from the anode
3
Q
Kirchoff’s Current Law(KCL)
A
At any point in an electrical circuit that does not represent a capacitor plate, the sum of currents flowing towards that point is equal to the sum of currents flowing away from that point.
4
Q
Direct Current/ DC (Types of Current)
A
- is one in which unidirectional current flows continously over time
- the flow of electric charge that does not change direction or values of intensity at the time of flow
- direction and intensity are constant
5
Q
The Reaction of Blood vessels
A
- Direct current causes vasodilatation
- This reaction which is expressed by redness in the skin, is more expressed under the electrodes, while around their environment is less pronounced
- Under the cathode vasodilatation is more intensely expressed than under the anode
6
Q
Pulsed Current/ PC (Types of Current)
A
- is one in which unidirectional or bidirectional flow of current periodically ceases over time
- intensity isn’t constant, but direction can be constant
7
Q
Action Potential
A
- a wave of electrical discharge that travels along the membrane of a cell
- it may be elicited by electrical, chemical, mechanical stimulation, by temperature change etc.
- can be created by many types of cells
- used mostly by the nervous system for communication between neurons and to transmit information from neurons to other body tissues such as muscles and glands
8
Q
Resting Membrane Potential/ RMP (part of Action Potential)
A
- takes place into account equilibrium potentials of all ions
- normal cell RMP= -70mV (interior of cell is negatively charged with respect to exterior)
9
Q
Electrical Current effects on human body
A
- Electrolysis
- Burns
- Muscle cramps
- Respiratory Arrest
- Cardiac arrest
- Ventricular fibrillation
10
Q
Electrolysis
A
- The movement of ions of opposite polarities in opposite directions through a medium is called electrolysis and can be made to occur by passing DC currents through body tissues or fluids.
11
Q
Depolarization (part of Action Potential)
A
- the loss of the normal negative value of the resting membrane potential
- opening up of sodium channels
12
Q
Burns
A
- When an electric current passes through any substance having electrical resistance, heat is produced
- The amount of heat depends on the power dissipated. Whether or not the heat produces a burn depends on the current density
- Human tissue is capable of carrying electric current quite successfully
- Skin normally has a fairly high electrical resistance while the moist tissue underneath the skin has a much lower resistance.
- Electrical burns often produce their most marked effects near to the skin, although it is fairly easy for internal electrical burns to be produced which if not fatal can cause long lasting injury
- the greater the surface area, the lesser the intesity/density(vice versa)
13
Q
Repolarization (part of Action Potential)
A
- the return of a cell’s membrane potential to resting potential after depolarization
- opening up of potassium channels
14
Q
Hyperpolarization (part of Action Potential)
A
the change in the membrane potential towards a more negative value
15
Q
Action Potential (diagram)
A
16
Q
Muscle cramps
A
- When an electrical stimulus is applied to a motor nerve or muscle, the muscle does exactly what it is designed to do in the presence of such a stimulus. ie. it contracts
17
Q
Respiratory arrest
A
- The muscles between the ribs(intercostalmuscles) need to repeatedly contract and relax in order to facilitate breathing
- Prolonged tetanus of these muscles can therefore prevent breathing
18
Q
Difference between Resting Membrane Potential and Action Potential
A
110mV
19
Q
Effect of Current on the Body
A
- tissues and systemic fluids exhibit differences in electrical conductivity, which depends on hydration and concentration of electrolytes contained in them
- best conductivity: nervous system (especially: cerebrospinal fluid)
- worst conductivity: circulation system, muscle tissue, fat tissue and bone tissue
20
Q
Cardiac arrest
A
- The heart is a muscular organ which needs to be able to contract and relax repetitively in order to perform its function as a pump for the blood. Tetanus of the heart musculature will prevent the pumping process
- Ventricular fibrillation can be triggered by very small electrical stimuli
- A current as low as 70mA flowing from hand to hand across the chest or 20microamps directly through the heart may be enough.
- It is for this reason that most deaths from electric shock are attributable to the occurrence of ventricular fibrillation
21
Q
Phase
A
- Phase: the current flow in one direction for finite period of time
22
Q
Anode (Electrode)
A
positively charged
23
Q
Cathode (Electrode)
A
negatively charged
24
Q
Cathodal Events
A
- depolarization of the nerve membrane occurs under the cathode
- as the electrical current flows from cathode to anode
- negative charges tend to accumulate on the outer surface of the nerve fibre membrane as they will be repelled by the negatively charged cathode
- the outside of the nerve fibre membrane is more negatve
- inside of the membrane becomes more positive due to accumulation of positive ions on the inside
- resting membrane potential will change towards a more positive value if depolarization occurs
25
Amplitude and Intensity
* **Amplitude**-the means of maximum value of current wih reference to the baseline
* **Intensity**- the magnitude of current or voltage applied by the unit and can be measured in **milliamps(mA)**
26
Anodal Events
* under the positively charged anode
* negative charges tend to move from the outside of the membrane towards the anode because they are attracted to the positive charge of the anode
* outside of the membrane is more positive, that has the effect of making the inside potential more negative and so hyperpolarization occurs
27
Ventricular Fibrillation
The ventricles of the heart are the chambers responsible for pumping blood out of the heart. When the heart is in ventricular fibrillation, the musculature of the ventricles unergoes irregular, uncoordinated twitching resulting in no net blood flow. The condition proves fatal if not corrected in a very short space of time.
28
Frequency
* **Frequency-** a number of pulses delivered per second. It is measured in Hertz(Hz) or in pulse per second(pps)
* **f=1/period**
* **T= tp+ti**
* Example: A frequency of 150 Hz means that 150 pulses are delivered per second
29
Electrochemical Effects
* are associated with electrolysis, which occurs during the flow of current through tissue electrolytes
* secondary reactions (which always occur during electrolysis), occur in the electric pads that separate electrodes from the skin, when electric treatments are performed
* if metal needle electrodes are introduced into the tissue, secondary reactions will occur around the environment of the electrodes
* these reactions occur between water and substances
30
Period
* Period: the time elapsed between a special point on the waveform of the pulse to the identical point on the next pulse
* In a pulsed current the period equals the pulse duration plus the interpulse interval
* In alternating current the waveform duration is equal to one period(one complete cycle)
31
Monobasic and Biphasic Waveform
* **A Monophasic Waveform:** the current flows in one direction, therefore one electrode acts as the cathode(negative) and the other as the anode(positive)
* **A Biphasic Waveform**- the current flow in both directions, so each electrode acts as a cathode for some part of the waveform
32
A Biphasic Waveform
* **Symmetrical:** the portion of the waveform in the first phase is an exact mirror image but opposite in direction to the portion of the waveform in the second phase
* **Asymmetrical**: the phase are not equal in shape
33
Electrolysis (Electrochemical Effects)
* lies in the fact that under the influence of the applied voltage (the difference potential) sodium ions move towards the cathode where they react with water
* 2Na+ 2H2O → 2NaOH + 2H2 (cathode)
* Chlorine ions move towards the anode and they also react with water. As a result of these reactions on the anode, it is produced hydrochloric acid and free oxygen
* 2Cl + H2O → HCl + O (anode)
34
Electrolytic Dissociation (Electrochemical Effects)
* the separation of the molecule of an electrolyte into its consituent atoms
* NaOH→ NA(+) + OH(-) (cathode)
* HCl→ H(+) + CL (-) (anode)
* as a result:
* under the cathode is produced the alkaline reaction
* under the anode is produced the acid reaction
35
Phase duration
* the time elapsed from the beginning to the end of one phase
36
Interphase interval
* the time between two successive componenets of a pulse when no electrical activity occurs
37
Electrokinetic Effect
* the dislocation of dispersed phase and distracting phase of tissue colloids relative to each other under the influence of an applied electric field
* Ex: electrophoresis
38
Waveform
* the visual representation of the current or voltage. The waveform of a current simply refers to its shape as seen on a graph of amplitude versus time
* Monophasic, Biphasic(symmetrical or asymmetrical)
39
Electrophoresis (Electrokinetic Effect)
* the movement of charged particles suspended in a liquid on various media under the influence of an applied electric field
* **Cataphoresis:** the movement of positively charged particles toward the cathode
* **Anaphoresis:** the movement of negatively charged particles toward the anode
40
Pulse duration
* the time elapsed from the beginning to the end of all phase in one pulse
41
Interpulse interval
* the time between two successive pulses
42
Rise time
* the time for the leading edge of the phase to increase from the baseline to the peak amplitude of the phase
43
Electroosmosis( Electrokinetic Effect)
* is the movement of the whole center, which means the distracting phase of colloids in relation to the dispersed phase
* the flow which is the result of the electric field acting on diffuse part of the double layer of the charge at the pore wall
* occurs on semi-permeable membranes which being impermeable for the dispersed phases, immobilize it on its surface
44
Decay time
* the time for the terminal edge of the phase to return to zero baseline from the peak amplitude of the phase
45
Current modulations
* PC and AC can be modulated. These modulations can be in amplitude and in frequency
* **Amplitude modulation**- a variation in the peak intensity in a series of pulses or cycle
* **Frequency modulation**- a variation in the instantaneous frequency of the wave
46
Electrothermal Effects
* the process of heating of tissues under the influence of an electric current
* heat which is produced in the tissue is the result of friction between ions and its environment
* amount of heat which is produced during the flow of direct current through tissues is slight and practically it does not substantially effect on the processes occuring in the tissues
* essential influence on the process of heating of the tissues exerts **vasodilation**
47
Surface(transcutaneous) electrode
* may be made of canvas, felt, metal, silicon, rubber or polymer
48
Surface stimulating electrodes
* Surface stimulating electrodes may require the use of a coupling medium, such as an electrolytic paste or gel
49
Flat electrodes
* Are usually made of thin foil with a thickness ensuring their plasticity. They adapt to body surface area.
* The electrode shape and type of coupling medium depend on:
* the tissue to be stimulated
* the type and duration of the examination
50
Reaction of Nerves and Muscles on the Current
* law formulated by **Du Bois Reymond:** cause of the electrical stimulus is not only the flow of current, but also a fast change of current intensity over time
* therefore, **direct current does not induce muscle contraction** during flow
* muscle contraction can only occur when we turn on and off direct current
* however, the change of intensity has to be sufficiently fast
51
Special electrodes
* have dimensions and shapes adapted to perform certain types of electric stimulation
* Examples: the electrodes which are used to perform electric treatment in the area around the eyes or ears and Bergonie half-mask electrode
52
Electrotonus (Reaction of Nerves and Muscles on the Current)
* flow of direct current through nerve tissue and muscle tissue causes the change in their excitability
* created by the movement of ions and changes in a cell's membrane potential, which occur during the flow of current
* **Catelectrotonus**: the state of increased excitability of the nerve or muscle that occurs under the cathode
* **Anelectrotonus**: the state of decreased excitability of the nerve or muscle near the anode
53
Invasive Electrodes
* are electrodes which are introduced into the tissues
* An example of the invasive electrode is needle electrode
54
Size of electrodes
* The size of the electrodes which are used to stimulation depends in part on the area of excitable tissue to be stimulated
* the size of the electrode determines the density of current flowing through it
* current density is the ratio of intensity to the surface by which electric current flows
* in the case where the size of both electrodes is the same, the current density is also the same under them
* If the surface of the electrodes is different, the current density will be greater under the electrode of smaller size
55
Stimulating electrode (active)
* **Stimulating electrode (active)** is placed over the target area, where the greatest effect is desired.
* **The electrode of smaller size has higher impedance, because electrode size is directly proportional to current flow**
56
Dispersive Electrode(inactive)
* **Dispersive Electrode(inactive)** is placed at some distance from the target area
* The electrode is larger in size than the stimulating electrode(larger size minimizes current density to the area to which it is applied)
57
Surface electrodes
* come into direct contact with the skin.
* These electrodes are used when the excitable tissue encompass a fairly large surface area, for example to record electromyogram signals from a large number of motor units and gross signals from a large superficial nerve.
58
Current Density
* J= I (Current in Amps) / S (surface area in m2)
* to calculate area of a circle, when it comes to needles: A= π r2
* is a measure of the density of electrical current
* defined as a vector whose magnitude is the electric current per cross-sectional area
59
Needle electrodes
* are used for recording _signals_ from small area
60
The Electric Battery
* zinc and carbon are used as electrodes
* a dilute solution: sulfuric acid (dilute) as electrolyte
* acid dissolves the zinc; causes zinc ions to leave the electrode
* each zinc ion which enters the electrolyte leaves 2 electrons on the zinc plate
* the carbon electrode also dissolves but at a slower rate
* result is a difference in potential between the two electrodes
61
Alternating Current/ AC (Types of Current)
* is one in which **bidirectional** current flows continously over time
* the flow of electric charge that periodically reverses direction
* **direction and intensity are not constant**
62
Parameters of electrical current
