Basic information about how the fundamentals of electronics and how they are important for intra-operative neuro-physiological monitoring on day to day basis. First chapter to read before you start IONM

1. ELECTRONICS &
IONM
ANURAG TEWARI MD

3. ELECTRICITY & ELECTRONICS
Virtually all of the intra operative neurophysiological monitoring is
based on ELECTRONS

4. ELECTRONICS
• The MANIPULATION of electrons, electrical charges
and their
• Electrostatic
• Magnetic
• Electromagnetic fields
To ACCOMPLISH a purpose

5. ELECTRICITY
Electricity is the set of physical phenomena associated with the
presence and flow of electric charge.

6. ELECTRICITY
• Depends upon the nature of electrical charges (electrons &
protons) and
• Electrostatic
• Magnetic
• Electromagnetic fields

7. ELECTRICITY
• The fundamental unit of the electrical charge is the
negatively charged ELECTRON
• Though, counterbalanced by the positively charged
PROTON
• In electronics, including the electrical devices, the unit of the
Sir Joseph John
Thomson
Nobel Prize 1906

8. ELECTRICITY
• Current flows from the
• NEGATIVE POLE (considered a relative excess of electrons)
to the
• POSITIVE POLE (considered a relative deficit of electrons)

9. FLOW OF ELECTRICITY
• CATHODAL CURRENT or the negative current is the flow of
electrons “from” the device
• ANODAL CURRENT or the positive current is the flow of
electrons “to” the device (flow of positive current to the
device)

10. ELECTRON
• Has a negative electrical charge creating an
ELECTROSTATIC field
• Static electricity
• Like walking on a carpet, touching a door knob
• Magnetic field
• Electrons spin, that means they are magnetic and/or
have a magnetic field
• Electrons can be affected by a magnetic field

11. ELECTRICITY IN BRAIN
• In the nervous system the fundamental unit of electricity is the ION
(charged atoms – unequal number of electrons or protons)
• The basic unit is still the ELECTRON, but here it is bound to the proton, and
not FREE as in a metal conductor (e.g. electronic devices)
• The CATION or positively charged ion
• Relative deficiency of electrons
• Na+, K+, Ca++
• The ANION or negatively charged ion
• Relative excess of electrons
• Cl-

12. SPIN OF AN ELECTRON

13. ELECTROMAGNETISM
• An accelerating or decelerating ELECTRON produces an electromagnetic
field, which is a combination of an electrostatic and magnetic field
• Thus, electromagnetic field has an effect on ELECTRONS by virtue of the
electrons electrical charge (static) and magnetism

14. ELECTROMAGNETISM

15. ELECTROMAGNETIC FORCES
• Requires accelerating electrical charges
• Constant flow of electrical charges produces a stable magnetic
field
• A changing (accelerating electrical charge produces a
fluctuating magnetic field)
• A stable magnetic field does not move electrical charges
• A fluctuating magnetic field moves electrical charges

17. ELECTROSTATIC, MAGNETIC &
ELECTROMAGNETIC FIELD AFFECTS
ELECTRONS
•These forces move ELECTRONS
•Purposeful in a controlled manner to allow
recordings of neuronal activity and for stimulation
•In the environment it causes noise & artifact
•Successful IONM requires precise control of these
forces

18. ELECTROSTATIC, MAGNETIC &
ELECTROMAGNETIC FIELD AFFECTS
ELECTRONS
• Stimulating electrodes activate neurons by electrostatic charges
• Neurons generate signals by changes in electrostatic charges
• Recoding Electrodes pick up signals by electrostatic mechanism
(CAPACITANCE)

19. ELECTROSTATIC, MAGNETIC &
ELECTROMAGNETIC FIELD AFFECTS
ELECTRONS
• Solid state amplification of electrical signals
• TRANSISTORS
• Valve that controls flow of electrons/current/voltage and
acts as a switch or gate for electronic signals
• A high voltage source (collector)
• A valve or base
• An output (emitter)

20. ELECTRIC CHARGE
• Electric charge is the physical property of matter that causes it to
experience a force when placed in an electromagnetic field
“like-charged objects repel and opposite-charged objects attract”
• By convention, the charge of an electron is −1, while that of a proton is
+1
• The SI unit of quantity of electric charge is COULOMB
• The charge of an electron is approximately −1.602×10−19 C
Charles-Augustin de Coulo

21. CHARGE = COULOMB
• The coulomb is defined as the quantity of charge that has passed through
the cross section of an electrical conductor carrying one ampere within one
second
C = Amp X Second
• It takes 6.242×1018 electrons to make one coulomb

22. CHARGE = COULOMB
•A lightening bolt is 10-20 coulombs
•A flash camera uses about 0.025 coulombs to
produce a flash
•In IONM we use microcoulombs

23. ELECTRIC CURRENT
• An electric current is a flow of charged particles through a
conducting medium
• In electric circuits this charge is often carried by moving
electrons in a wire
• It can also be carried by ions in an electrolyte, or by both ions
and electrons such as in a plasma
I = Q/t
Where I = Current in Amperes (Coulombs per second)
André-Marie
Ampère

24. ELECTRIC CURRENT
• One AMPERE is approximately equivalent to 6.2415093×1018
elementary charges moving past a boundary in one second
Why is current represented by an I
intensité de
courant

25. VOLTAGE
• Voltage, also called electromotive force, is a quantitative expression of the
potential difference in charge between two points in an electrical field
• The voltage between two points is equal to the work done per unit of
charge against a static electric field to move the test charge between two
points and is measured in units of volts (a joule per coulomb)
• A voltage may represent either a source of energy (electromotive force), or
lost, used, or stored energy (potential drop)
• The greater the voltage, the greater the flow of electrical current
• Measure in Volts

26. RESISTANCE
• Forces that oppose the flow of the electrical charges
• In METAL conductors
• Outer shell electrons around the metal ions loosely held
• Metal atoms have relatively few electrons in outer orbits and lots of vacant spots
where electrons can move into
• In BRAIN conductors
• Resistance to the movement of ions

30. RESISTANCE OF THE FLOW OF ELECTRIC
CHARGE
• Many factors can impede the flow of the electrical charges
• In METALS
• The typical notion of resistance relates to how tightly the
electrons are held to the atoms of the material
• Tight bond gives rise to high resistance
• Electrostatic magnetic and electromagnetic forces add to resistance, to
create IMPEDANCE

31. RESISTANCE VERSUS IMPEDANCE
• Resistance is one type of opposition to the flow of
electrons
• IMPEDANCE
• General term for opposition
• IMPEDANCE = Resistance + Reactance
• REACTANCE
• Effect of electrostatic and magnetic forces created by the
flow of the electrical changers that acts against the flow of
the electrical charges, i.e.
• Inductance

32. IMPEDANCE
• The opposition to the flow of current
• Two components
• Resistance
• Reactance
• Two components
• CAPACITIVE (electrostatic) reactance
• INDUCTIVE (magnetic) reactance

34. IMPEDANCE
• CAPACITIVE REACTANCE (Electromagnetic)
• Requires a change in the electrical conductivity
• In a single pure conductor NO change in electrical conductivity
• INDUCTIVE REACTANCE (Magnetic)
• To have an effect on flow of electrical charges, induced magnetic field
must fluctuate
• For magnetic field to fluctuate, the flow of electrical charges must
fluctuate
• NOT the case in DC electronics and hence
• INDUCTIVE REACTANCE IS NOT A FACTOR IN IMPEDANCE IN DIRECT

35. CAPACITIVE REACTANCE
• Related to capacitance
• Any object that can be electrically charged exhibits capacitance
• The SI unit of capacitance is the farad (symbol: F), named after the English physicist
Michael Faraday.
• Typical example: The CAPACITOR: One that stores CHARGE
• Farads are the number of coulombs that can be stored per volt: F =C/V
• 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential
difference of 1 volt between its plates
Michael
Faraday

36. CAPACITIVE REACTANCE
• Occurs when there is DISCONTINUITY of the dielectric constant in the
flow of electrical charges
• Creates an electrostatic charge or field
• Inhomogeneity within the conductor
• Including brain at the boundary of grey and white matter (white matter has higher
dielectric constant)
• At connections between different conductors
• Conductors do not have to be in physical continuity
DIELECTRIC CONSTANT: a quantity measuring the ability of a substance to store electrical energy in
an electrical field

37. INDUCTIVE REACTANCE
• Electromagnetism
• Flow of electrons through a conductor generate magnetic fields
• In a straight conductor
• In coil
• Movement of a conductor through a magnetic filed causes the
electrons to flow
• Electrons are mini-magnets, hence can be moved by a magnetic field
• Flowing electrons give rise to CURRENTS
• The faster the magnetic field moves, the faster the electrons move and
greater the current

38. INDUCTIVE REACTANCE
• Flow of electrons in a straight conductor
• Expanding and falling currents create expanding and collapsing
magnetic fields
• The expanding and collapsing magnetic field essentially moves
the magnetic field of the same conductor
• Induces a voltage or current that opposes the original flow of
electrons

39. OHM’S LAW
• Ohm's law states that the current through a conductor between
two points is directly proportional to the voltage across the two
points.
Georg
Ohm

40. OHM’S LAW IN DC ELECTRONICS
• Direct Current (DC) electronics means a single or non-varying
electrical current
• Resistance is the biggest factor
• Impedance is less of a factor

41. OHM’S LAW IN AC ELECTRONICS
• In alternating current or time varying currents
• We replace the Resistance with IMPEDANCE
• Does our nervous system have AC or DC current flowing
through them?

42. In nerves the NERVE ACTION POTENTIAL is generated at a
frequency of 40-50Hz