Electronics and Intra Operative Neurophysiological Monitoring
- 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