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MEDICAL BIOPHYSICS > ELECTRICITY AND HUMAN BODY > Flashcards

ELECTRICITY AND HUMAN BODY Flashcards

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USMLE® Step 1 flashcards
1
Q

ELECTRIC CURRENT

A

flow of electric charge through a conductive medium

CURRENT = VOLTAGE / RESISTANCE
I = U/R

-> higher the voltage higher the current
-> higher the resistance lower the current

CONDUCTORS OF 1ST CLASS = metals
CONDUCTORS OF 2ND CLASS = electrolytes

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2
Q

ELECTRIC VOLTAGE

A

difference of electric potentials of 2 places

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3
Q

ELECTRIC POTENTIAL

A

free charged particles move from places of high concentration to places with low concentration = electric current

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4
Q

ALTERNATING CURRENT

A

the voltage is changing (electrical outlet). Number of cycles in 1 second is called frequency (measured in Hertz)
-can flow intracellularly

1mA at 50-60Hz

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5
Q

DIRECT CURRENT

A

voltage does not change
-battery
-also called galvanic
-when it passes through tissues it causes electrolytic changes
-best conductors are blood, cerebrospinal fluid and muscles
-resistors include adipose, fibrous, cell membrane
-irritant effect only felt when switched on or off

5 mA at 50-60Hz

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6
Q

RESISTANCE OF SKIN

A

KERATINIZED DRY: 20-30 k/cm2
THIN MOIST: 0.5k/cm2
PUNCTURED: 0.25K/cm2

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7
Q

WHAT CAN HIGH RESISTANCE CAUSE?

A

much energy and can cause burns
-THE HIGHER THE RESISTANCE THE HIGHER THE PRODUCTION OF HEAT
- Q = I2.R
-skin, fat, tendon, bone all have higher resistance than nerves, blood vessels and muscles

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8
Q

WHAT CAN LOW RESISTANCE CAUSE?

A

cardiac arrest may occur if reaches heart

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9
Q

WHAT IS THE “LET GO” CURRENT?

A

The level where we lose control of our muscles, and the electricity will cause the muscles to contract until the current is removed.

The let-go range is between 6-16 mA.
Normally around 9 mA in females and 15 mA for male.

The minimum current a human can feel depends on the current type (AC or DC) and frequency.
-A person can feel at least 1 mA of AC at 50-60 Hz, while at least 5 mA for DC. The current may, if it is high enough, cause tissue damage or fibrillation which leads to cardiac arrest. -
-Current of 60 mA of AC or 300–500 mA
of DC can cause fibrillation.

Amount of current flowing through the body (measured in amperes)

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10
Q

RESISTANCE OF HUMAN SKIN

A

under dry conditions very resistant
under wet conditions resistance dramatically drops

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11
Q

RHEOBASE

A

The minimal current amplitude that will result into a muscle contraction or depolarization of neuron

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12
Q

UNIT OF INDUCTANCE

A

Henry

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13
Q

UNIT OF ELECTRIC RESISTANCE

A

Ohm

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14
Q

UNIT OF ELECTRIC CHARGE

A

Coloumb

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15
Q

UNIT OF ELECTRIC CAPACITY

A

Farad

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16
Q

UNIT OF ELECTRIC CONDUCTANCE

A

Siemens

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17
Q

UNIT OF MAGNETIC FLUX

A

Weber

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18
Q

UNIT OF MAGNETIC INDUCTION

A

Tesla

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19
Q

WHAT STIMULATES A DENERVATED MUSCLE?

A

triangle impulse

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20
Q

WHAT STIMULATES A HEALTHY MUSCLE?

A

rectangular impulse

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21
Q

HOW DOES A HEALTHY MUSCLE REACT TOWARDS AN OBLIQUE PULSE IN ELECTROTHERAPY?

A

-muscle adapts
-muscle doesnt react

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22
Q

WHAT IS THE CELL MEMBRANE IMPEDANCE DURING INCREASING FREQUENCY OF ALTERNATING CURRENT?

A

-decreases with increasing frequency of the alternating current

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23
Q

WHEN ARE THERMAL EFFECTS OF THE DIRECT CURRENT SEEN?

A

only during the currents with maximum amplitudes, otherwise the thermal effect is insignificant

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24
Q

WHEN ARE THE EXCITABLE EFFECTS OF THE DIRECT CURRENT SEEN?

A

upon only switching on/off or during the increasing/decreasing of the current

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25
Q

WHEN CAN A SUBSTANCE PRODUCE A CURRENT?

A

only if it contains free charged particles

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26
Q

WHICH INTERNAL TISSUES CONDUCT MORE ELECTRICITY?

A

nerves, blood vessels, muscles

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27
Q

WHAT ARE THE ECM AND ICM IN TERMS OF ELECTRICITY?

A

electrolytes, good conductors

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28
Q

WHAT ARE CELL MEMBRANES IN TERMS OF ELECTRICITY?

A

good insulators

29
Q

LET GO CURRENT

A

the maximum amperage that can cause flexors of the arm to contract but that allows person to release hand from current source

AC = 15 mA
DC = 75mA

30
Q

THRESHOLD OF PERCEPTRION OF CURRENT ENTERING THE HAND

A

AC = 1-5 mA
DC = 5-10 mA

31
Q

DAMAGE CAUSED BY ELECTRIC SHOCK

A

1mA = FELT PAIN
5mA = PAINFUL
>15mA = LOSS OF MUSCLE CONTROL
70mA = FATAL

32
Q

WHICH CURRENT IS MORE DANGEROUS?

A

AC
-especially at low frequencies 50-60Hz as it causes muscle tetany, freezing the hand to the currents source

33
Q

WHAT DETERMINES THE NATURE OF THE INJURY?

A

body pathway of the current

34
Q

ACCOMODATION QUOTIENT FOR HEALTHY MUSCLE

A

3-6
-TRIANGLE PULSES GREATER THAN RECTANGULAR

35
Q

ACCOMODATION QUOTIENT FOR DENERVATED MUSCLE

A

1-2.7
-CONTRACTION CAUSED BY OBLIQUE MUSCLES WITH SAME INTENSITY AS RECTANGULAR

36
Q

WHAT IS THE EFFECT OF PHYSICAL EXERCISE ON THE RHEOBASE?

A

-decreased rheobase
-increased neuromuscular sensitivity

-> K+ efflux, hyperpolarization, excitability of muscle reduced, more intense and longer electrical stimulation needed for contraction

->sportsmen less likely to have rheobase increase after acute exercise as they have more proton pumps in neuromuscular junctions and lower resting membrane potential

37
Q

DEFIBRILLATION

A

-common treatment for ventricular fibrillation
-driving an electrical shock to cardiac cells
-when cardiac cells are depolarized they can attempt to restore normal heart rhythm

38
Q

PACEMAKER

A

device for electrical stimulation to cause cardiac contraction when intrinsic cardiac electrical activity is slow or absent

-stimulation of cardiac depolarization
-sensing intrinsic cardiac function
-responding to increased metabolic demand

39
Q

tDCS

A

modulate excitation and or inhibition of brain

40
Q

tACS

A

to change oscillatory brain stress

41
Q

tRNS

A

to induce excitation and plasticity in the brain

42
Q

GALVANOTHERAPY

A

therapeutic use of DC current

43
Q

WHAT ARE THE MAIN EFFECTS OF THE LOW FREQUENCY AC?

A

-excitable effect of current increases with increasing frequency
-thermal and electrolytic effects are insignificant

44
Q

WHAT MUST BE OBEYED WHEN HEATING TISSUES WITH CURRENTS OF HIGH FREQUENCY?

A

the shorter the wavelength, the more even the heating of the tissue

45
Q

WHAT IS ELECTROPHORESIS USED FOR IN MEDICINE?

A

splitting plasma proteins
-> most important electrokinetics

46
Q

WHAT IS THE RESULT OF THE FLOW OF CHARGED PARTICLES IN GALVANOTHERAPY?

A

-alkaline under negative electrode cathode used for treatment of paralysis and reduced sensitivity
-acidic under positive electrode anode

47
Q

CONTRAINDICTIONS OF ELECTROTHERAPY

A

-cancer
-allergies
-gravidity
-application around eyes and heart

48
Q

ELECTROPHORESIS

A

-diagnostic method
-with suitable pH ions and proteins will travel in a direct electrical field

49
Q

WHAT ARE THE GENERAL EFFECTS OF ELECTRIC CURRENT?

A

excitable
thermal
electrolytic

50
Q

WHAT ARE THE COMPONENTS OF A DIADYNAMIC CURRENT?

A

galvanic
puls-like low frequency current

51
Q

MAGNETIC FIELD

A

-stationary magnetic field arises around permanent magnets
-for stationary magnetic field, electrical component is 0
-in the electrostatic field, the magnetic component is 0
-we distinguish stationary, alternating and pulsed magnetic fields

52
Q

WHAT TISSUES OFFER THE HIGHEST RESISTANCE TO DC?

A

-cell membrane
-connective tissue
-adipose tissue

53
Q

WHAT APPLIES TO ULTRASHORT WAVE DIATHERMY?

A

-thermal exchange occurs due to the influence of electromagnetic waves emitted
-patients blood circulation is improved

54
Q

WHAT IS THE MEANING OF THE i/t CURVE IN ELECTROTHERAPY?

A

dependance of the stimulating impulse current intensity on its width

55
Q

WHAT IS THE MAIN USE OF IONTOPHORESIS?

A

delivery of medicine

56
Q

WHAT COMPONENTS IS THE CELL MEMBRANES IMPEDANCE COMPRISED OF?

A

-resistance
-capacitance

57
Q

WHAT IS THE WIDTH OF STIMULATIVE CURRENTS TO WHICH A HEALTHY MUSCLE REACTS TO?

A

5 to 10 ms

58
Q

WHAT ARE ELECTROLYTES THE RESULT OF?

A

electrolytic dissociation of electrically neutral molecules

59
Q

GALVANOTHERAPY

A

-therapeutic use of DC current with constant intensity of the current density of 0.1mA/cm2
-electrolytical effect
-skin, bone, cartilage and tendon show most resistance
-elastic current passes through tissues with high water content and proteins
-acidic under positive electrode anode for pain control
-alkaline environment under negative electrode cathode used for paralysis treatment

60
Q

IONTOPHORESIS

A

uses motion of ions in a DC electric field for injecting electrically charged molecules of drugs into the organism
-drug under small active electrode
-second indifferent electrode is relatively large and attaches to any part of the body

61
Q

EXPLAIN THE RESISTANCE OF THE CELL MEMBRANE

A

resistance of cell membranes decreases with increasing frequency of AC
= IMPEDANCE OF MEMBRANE
#capacitance
#resistance

62
Q

ELECTRO-STIMULATION

A

-also called pulse therapy
-uses the irritating effects of low frequency currents
-used to stimulate muscles to prevent it from wasting away after fractures or post operative stress

63
Q

WHEN ARE TRABERT CURRENTS USED?

A

-states after intense injuries in order to relieve nerve and muscle pain
-significant analgesic and hyperaemic effects

64
Q

WHAT IS THE MAIN DIFFERENCE BETWEEN INCREASING AND DECREASING FREQUENCIES OF ALTERNATING CURRENTS?

A

INCREASING = causes decreasing irritation
-no electrolytic effects just heat
-resistance and capacitance of cell membrane decrease

DECREASING = causes increasing irritation
-no thermal effects just electrolytic effects

65
Q

SHORTWAVE DIATHERMY

A

-induction field heated by insulated cable wraps around target body part
-alternating magnetic field generates high frequency eddy currents in the tissue and energy is converted to heat
-skin warms less, muscles warm more
-deep hyperaemia, spasmolytic effects, analgesic effects, increased capillary permeability, softening of fibrous adhesions

66
Q

WHAT IS THE MAIN AIM OF ULTA SHORT WAVE DIATHERMY?

A

lowers blood pressure in patients with high blood pressure
-muscles have maximum absorption
-small heat load of fat and skin

67
Q

DENERVATED MUSCLE

A

-100ms or less
-rises steeply and is shift to the right
-long triangular pulse required

68
Q

WHEN DO DENERCATED AND INERVATED MUSCLES CROSS ON THE CURVE?

A

50-100 ms

69
Q

INNERVATED MUSCLE

A

-rectangular waveform
-1 to 600ms
-can react to triangular by adaptation, for pulses longer than 20-50ms triangular must be stronger than that of rectangular

MEDICAL BIOPHYSICS (9 decks)

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