Concepts of Therapeutic Electric Current Flashcards
Types of kinetic energy
- thermal (energy of moving particles-heat)
- mechanical (energy of objects in motion)
- electrical (energy of particles moving though a wire)
- magnetic (energy causing push or pull)
Types of potential energy
- chemical (energy stored in food or fuel)
- elastic (energy stored in objects that are stretched)
- nuclear (energy stored in center of particles)
- gravitational (energy stored in an object when it’s above earth’s surface)
Ways energy is transferred
conduction = transfer through direct contact (touching a hot pot)
convection = transfer through liquid or gas from the movement of the particles (oven, boiling water)
conversion = change of energy from one state to another (water or wind to electricity)
Electric charge
physical property of matter that causes it to experience of force when placed in an electric field
How is electric charge carried out?
subatomic particles which determine electromagnetic interaction
What is the source of the electromagnetic force?
the interaction between a moving charge and an electromagnetic field
Electricity
type of energy that can build up in one place or flow from one place to another
Static electricity
when electricity gathers in one place
- potential energy
ex: a battery
Current electricity
electricity that moves from one place to another
- kinetic energy
How is electricity “made”?
caused by electrons that orbit around atoms
- electrons have a NEGATIVE charge
Why is there no charge in atoms?
they have equal amounts of protons and electrons (positive and negative charges)
Why do electricity flow easily through metal but not rubber?
- metals have “free” electrons that are not bound tightly to the parent atoms which enables electric current flow
- rubber has more “bound” electrons which prevents flow of the electric current
Predictable behaviors of charges:
- opposite charges attract
- like charges repel
- charges can’t be created or destroyed
- charges can be transferred from object to object
Cation
atom losses electrons in its outer shells without changing the number of protons it has in its nucleus
- POSITIVE charge
Anion
atom gains electrons in its outer shell
- NEGATIVE charge
Ions
atom with either an excess or deficiency of electrons
Coulombs law
- force created by 2 particles is equal to the strength and charge
- force created by 2 particles is inversely proportional to the distance
Electrical potential difference
potential energy that is converted to kinetic energy when particles are approximated
Electromotive force (EMF)/Voltage
movement of particles
Current
movement of charged particles through a conductor in response to an applied electrical field of voltage
What is responsible for the physiological changes during electrical stimulation?
current, the transfer of energy from one point to another
What do you need to have a current?
- driving force to move the particles (current generator)
- conductive pathway (wires, electrodes, excitatory cells)
- difference in electrical potential (generator to body)
Why does current flow from generator to body?
the body has a lower electrical potential than the generator
OHM’s law
current (I) = voltage (V) / resistance (R)
magnitude of current in a conductor is INVERSELY PROPORTIONAL to resistance and PROPORTIONAL to voltage
Constant voltage stimulators
don’t adjust voltage in response to impedance
Resistance
the opposition to direct current flow through a conductor in a circuit
Series circuit
- component resistors are side by side w/ ends connected (one pathway)
- flow is inversely proportional to resistance
- total voltage is sum of all the voltages at each component
Parallel circuit
- component resistors create multiple pathways
- flow depends on resistance
- total voltage is the same of voltage at each component
What happens with a greater impedance of the skin?
the voltage of the electrical current needs to be higher
- chemical changes in the skin make it more resistant to certain types of current
Capacitance
ability of the conductor or insulator to store electrical charge before an action potential occurs
What does a time constant describe in cell membranes?
each excitable cell membrane has a time constant that describes the rise and decay of electrical potentials
Time constant
the product of the membrane’s resistance and capacitance
What does a time constant do?
determines the MIN duration that a stimulus must exist before the cell’s threshold for depolarization is reached
Impedence
opposition to alternating current
- sum of resistive, capacitive, and inductive components of the tissue (impair current flow)
- PARTIALLY affected by the frequency of the applied electrical current
- INVERSELY proportional to the applied frequency
What is the normal resting membrane potential of a peripheral nerve?
-70mV
created by the difference between the inside of the cell membrane (NEGATIVE) and the outside of the cell membrane
Muscle and nerve membrane ions:
Na+ is higher outside
K+ is higher inside
each ion will want to move across the membrane to equal out the concentration
Leak channels
membranes are more permeable to K+ so more K+ will move out of the cell
- creates a net negative charge inside cell
- loss of K+ will stop as the cell becomes more negative and will require a positive charge to move back into cell
Action potentials
if a stimulus is introduced, the cell membrane can change its permeability to Na+
- Na+ moves into cell to reduce negative charge inside
- increase in positive charges inside will hit a threshold and a thrust of Na+ will enter (DEPOLARIZATION)
When will depolarization occur?
at -55mV
Initial activity increased permeability to K+ to cause?
the membrane to become more negative (HYPERPOLARIZATION)
- happens after Na+ change
Excitable cell
a cell that has the ability to generative an action potential
What is threshold determined by?
- amplitude which will vary from membrane to membrane
- duration of the stimulus
Absolute refractory period
membrane needs 1-2 msec to recover excitability after an action potential
Relative refractory period
membranes needs .5-1 msec to recover excitability after an action potential of a higher stimulus
