1. ELECTRIC CURRENTS BY
B.Nelson

2. Aims of Presentation Outline the basic principles of electricity
Explain the physiological responses to electricity

3. What is electric current ?
Net movement of electrons through a conductor
Electrons are particles of matter which are negatively charged and have a small mass
Electrons will move from an area of high potential to an area of lower potential

4. Components of electrical current
Ampere(A) : unit of measure that indicates the rate at which electrical current is flowing
Coulomb :the number of electrons flowing per second
1 ampere = 1 coulomb/ 1 second

5. Components of electrical current
Conductor : materials that permit free movement of electric current (metals)
Insulators : materials that resist the flow of electric current (wood , glass)

6. Basic Types of current Direct current (DC/galvanic)
Alternating current (AC)

7. Types of current cont’d
Direct current :unidirectional flow of electrons from the negative to the positive poles,e.g batteries
Alternating Current: continuous bidirectional flow of electrons from negative to positive poles ,e.g outlets in the home produce AC

8. Waveforms
Indicates a graphic representation of the shape ,direction ,amplitude ,duration and frequency of the current produced by the device
Electrical currents may take on a Sinusoidal,
Rectangular, square or spiked waveform shape

9. Waveforms Cont’d

10. Components of electrical current
Pulse amplitude : reflects the intensity of the current and is measured in amperes(amp/A)
Pulse duration :the length of time current is flowing in one cycle
Pulse frequency: number of pulses or cycles per second and is measured in Hertz (Hz)

11. Current flow through biologic tissue
Flows through the path of least resistance
Tissue with highest water content & ion content best conductor of electricity
Skin is considered an insulator as it offers primary resistance to current
Muscle conducts electric current effectively
Muscle- tendon unit and fat are poor conductors

12. Physiological responses to electrical currents
Electrical currents are used to :
Produce muscle contractions
Modification of pain through effects on motor and sensory nerves

13. Effects of electrical impulses
Nerve Depolarisation
Muscle depolarisation
Ionic effects of electrical currents

14. Nerve Depolarisation Action potential : basic unit of communication
Within the nerve
Strength – duration curve: a graphic representation of quantity of current required to produce an action potential in a nerve
SDC varies for different types of nerves

15. Sensory nerves: low current amplitude/intensity and short pulse durations can depolarise- less than 80 microseconds
Motor nerves : high current amplitude/intensity and longer pulse duration cad depolarise microseconds
Pain transmitting C –fibres: higher current intensity and longer pulse duration- 10 milliseconds and over

16. Longer pulses of 10ms are required to depolarise muscle cell of denervated muscle
This type of stimulation stimulates the A-delta and C-fibres – when present
Uncomfortable for patient

17. Rheobase: minimum current ampitude/intensity with long duration required to produce an action potential
Chronaxie: minimum time to stimulate the tissue at twice the rheobase intensity
Chronaxie and rheobase are used in electromyography

18. Electromyography ; analysing and recording electric activity in skeletal muscles
Used to diagnose neuropathies, myopathies ect

19. Accommodation
`process where the nerve becomes less responsive to stimulation
Action potential travels faster in large –diameter myelinated nerves than in small- diameter unmyelinated fibres

20. Muscle depolarisation
Innervated muscle contract due to depolarisation of motor nerves
Denervated muscles contract due to depolarisation of muscle cell membrane
Denervated muscles require longer pulse duration (> 10 ms) to produce muscle contraction
Muscles do not accommodate

21. +++++++++++++ Ionic effects of electrical currents
Cathode (neg. electrode)attracts positively charged ions, while the anode(+ electrode) attracts negative electrode
Iontophoresis : process where direct current is used to facilitate transdermal drug penetration
Used to treat during the inflammatory stages, facilitate tissue healing and decrease oedema