ELECTRICITY AND HUMAN BODY Flashcards
ELECTRIC CURRENT
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
ELECTRIC VOLTAGE
difference of electric potentials of 2 places
ELECTRIC POTENTIAL
free charged particles move from places of high concentration to places with low concentration = electric current
ALTERNATING CURRENT
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
DIRECT CURRENT
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
RESISTANCE OF SKIN
KERATINIZED DRY: 20-30 k/cm2
THIN MOIST: 0.5k/cm2
PUNCTURED: 0.25K/cm2
WHAT CAN HIGH RESISTANCE CAUSE?
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
WHAT CAN LOW RESISTANCE CAUSE?
cardiac arrest may occur if reaches heart
WHAT IS THE “LET GO” CURRENT?
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)
RESISTANCE OF HUMAN SKIN
under dry conditions very resistant
under wet conditions resistance dramatically drops
RHEOBASE
The minimal current amplitude that will result into a muscle contraction or depolarization of neuron
UNIT OF INDUCTANCE
Henry
UNIT OF ELECTRIC RESISTANCE
Ohm
UNIT OF ELECTRIC CHARGE
Coloumb
UNIT OF ELECTRIC CAPACITY
Farad
UNIT OF ELECTRIC CONDUCTANCE
Siemens
UNIT OF MAGNETIC FLUX
Weber
UNIT OF MAGNETIC INDUCTION
Tesla
WHAT STIMULATES A DENERVATED MUSCLE?
triangle impulse
WHAT STIMULATES A HEALTHY MUSCLE?
rectangular impulse
HOW DOES A HEALTHY MUSCLE REACT TOWARDS AN OBLIQUE PULSE IN ELECTROTHERAPY?
-muscle adapts
-muscle doesnt react
WHAT IS THE CELL MEMBRANE IMPEDANCE DURING INCREASING FREQUENCY OF ALTERNATING CURRENT?
-decreases with increasing frequency of the alternating current
WHEN ARE THERMAL EFFECTS OF THE DIRECT CURRENT SEEN?
only during the currents with maximum amplitudes, otherwise the thermal effect is insignificant
WHEN ARE THE EXCITABLE EFFECTS OF THE DIRECT CURRENT SEEN?
upon only switching on/off or during the increasing/decreasing of the current
WHEN CAN A SUBSTANCE PRODUCE A CURRENT?
only if it contains free charged particles
WHICH INTERNAL TISSUES CONDUCT MORE ELECTRICITY?
nerves, blood vessels, muscles
WHAT ARE THE ECM AND ICM IN TERMS OF ELECTRICITY?
electrolytes, good conductors
WHAT ARE CELL MEMBRANES IN TERMS OF ELECTRICITY?
good insulators
LET GO CURRENT
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
THRESHOLD OF PERCEPTRION OF CURRENT ENTERING THE HAND
AC = 1-5 mA
DC = 5-10 mA
DAMAGE CAUSED BY ELECTRIC SHOCK
1mA = FELT PAIN
5mA = PAINFUL
>15mA = LOSS OF MUSCLE CONTROL
70mA = FATAL
WHICH CURRENT IS MORE DANGEROUS?
AC
-especially at low frequencies 50-60Hz as it causes muscle tetany, freezing the hand to the currents source
WHAT DETERMINES THE NATURE OF THE INJURY?
body pathway of the current
ACCOMODATION QUOTIENT FOR HEALTHY MUSCLE
3-6
-TRIANGLE PULSES GREATER THAN RECTANGULAR
ACCOMODATION QUOTIENT FOR DENERVATED MUSCLE
1-2.7
-CONTRACTION CAUSED BY OBLIQUE MUSCLES WITH SAME INTENSITY AS RECTANGULAR
WHAT IS THE EFFECT OF PHYSICAL EXERCISE ON THE RHEOBASE?
-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
DEFIBRILLATION
-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
PACEMAKER
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
tDCS
modulate excitation and or inhibition of brain
tACS
to change oscillatory brain stress
tRNS
to induce excitation and plasticity in the brain
GALVANOTHERAPY
therapeutic use of DC current
WHAT ARE THE MAIN EFFECTS OF THE LOW FREQUENCY AC?
-excitable effect of current increases with increasing frequency
-thermal and electrolytic effects are insignificant
WHAT MUST BE OBEYED WHEN HEATING TISSUES WITH CURRENTS OF HIGH FREQUENCY?
the shorter the wavelength, the more even the heating of the tissue
WHAT IS ELECTROPHORESIS USED FOR IN MEDICINE?
splitting plasma proteins
-> most important electrokinetics
WHAT IS THE RESULT OF THE FLOW OF CHARGED PARTICLES IN GALVANOTHERAPY?
-alkaline under negative electrode cathode used for treatment of paralysis and reduced sensitivity
-acidic under positive electrode anode
CONTRAINDICTIONS OF ELECTROTHERAPY
-cancer
-allergies
-gravidity
-application around eyes and heart
ELECTROPHORESIS
-diagnostic method
-with suitable pH ions and proteins will travel in a direct electrical field
WHAT ARE THE GENERAL EFFECTS OF ELECTRIC CURRENT?
excitable
thermal
electrolytic
WHAT ARE THE COMPONENTS OF A DIADYNAMIC CURRENT?
galvanic
puls-like low frequency current
MAGNETIC FIELD
-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
WHAT TISSUES OFFER THE HIGHEST RESISTANCE TO DC?
-cell membrane
-connective tissue
-adipose tissue
WHAT APPLIES TO ULTRASHORT WAVE DIATHERMY?
-thermal exchange occurs due to the influence of electromagnetic waves emitted
-patients blood circulation is improved
WHAT IS THE MEANING OF THE i/t CURVE IN ELECTROTHERAPY?
dependance of the stimulating impulse current intensity on its width
WHAT IS THE MAIN USE OF IONTOPHORESIS?
delivery of medicine
WHAT COMPONENTS IS THE CELL MEMBRANES IMPEDANCE COMPRISED OF?
-resistance
-capacitance
WHAT IS THE WIDTH OF STIMULATIVE CURRENTS TO WHICH A HEALTHY MUSCLE REACTS TO?
5 to 10 ms
WHAT ARE ELECTROLYTES THE RESULT OF?
electrolytic dissociation of electrically neutral molecules
GALVANOTHERAPY
-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
IONTOPHORESIS
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
EXPLAIN THE RESISTANCE OF THE CELL MEMBRANE
resistance of cell membranes decreases with increasing frequency of AC
= IMPEDANCE OF MEMBRANE
#capacitance
#resistance
ELECTRO-STIMULATION
-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
WHEN ARE TRABERT CURRENTS USED?
-states after intense injuries in order to relieve nerve and muscle pain
-significant analgesic and hyperaemic effects
WHAT IS THE MAIN DIFFERENCE BETWEEN INCREASING AND DECREASING FREQUENCIES OF ALTERNATING CURRENTS?
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
SHORTWAVE DIATHERMY
-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
WHAT IS THE MAIN AIM OF ULTA SHORT WAVE DIATHERMY?
lowers blood pressure in patients with high blood pressure
-muscles have maximum absorption
-small heat load of fat and skin
DENERVATED MUSCLE
-100ms or less
-rises steeply and is shift to the right
-long triangular pulse required
WHEN DO DENERCATED AND INERVATED MUSCLES CROSS ON THE CURVE?
50-100 ms
INNERVATED MUSCLE
-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
