Bio-Electronics Course Outline

Contact Information

• Contact Mohamed Ahmed Sabet Hammam, PhD in Solid State Physics from Assiut University, at [email protected] or [email protected] and through Whatsapp group +201006773115.
• Office hours are 2 hours/week in Bio413, 3rd floor.

Biophysics Lecture Timing

• Lectures consist of a 15-minute refreshment break, 90 minutes of explanation, and 15 minutes for questions and answers.

Course Assessment Grades

• Class work and quizzes: 15 points
• Midterm: 10 points
• Practical class work: 10 points
• Practical final: 5 points
• Oral exam: 10 points
• Final exam: 50 points
• Sum of all assessments: 100 points
• You must exceed 60% of the total course points to pass.

Bio-Electronics: Key Topics

• Electric Current
• Circuit Components
• Impedance
• Semiconductors
• PN-Junction
• Forward Bias
• Reverse Bias
• Light-Emitting Diodes (LEDs)
• Photoresistors
• Cell Membrane
• Membrane Transport and Active Transport
• Membrane Potential
• Biological Cells as Capacitors
• Structure of Neuron
• Types of Neurons
• Action Potentials
• Synapse
• Bio-impedance
• Pulse Oximeter
• Electroencephalography
• Electromyography
• Electrocardiogram
• Pacemakers
• Defibrillators
• Neuromodulation Devices
• Electrical Muscle Stimulation
• Cochlear Implant
• Diathermy

Electric Current

• Electric current involves the flow of charged particles, such as electrons or ions through an electrical conductor or space
• It is measured in Amperes (Coulomb/Second)
• Conventional current is the flow of positive charge from positive to negative.
• I = Q/t, where I is current, Q is charge, and t is time

Current Types

• Electronic Conduction: In metals, from the motion of free electrons in an electric field.
• Ionic Conduction: In electrolytes, from charged ions in acids, bases, and salts.
• DC (Direct Current): Unidirectional flow of electric charge with constant magnitude.
  • I = I₀ = constant value
• AC (Alternating Current): Direction and magnitude of electric charge flow changes periodically (sin or cos functions).
  • I = I₀sin(ωt) (wave function)
  • where I₀ is the maximum magnitude, t is time, ω = 2πf is the angular frequency, and f is the frequency.

Power Sources

• Power sources generate electrical energy in an active network.
• Ideal Voltage Source: Two-terminal device with constant average voltage, independent of drawn current
• Ideal Current Source: Two-terminal device supplying the same average current to any load resistance; current is independent of the voltage; has infinite resistance.

Resistance

• Resistance opposes current flow in an electrical circuit.
• Measured in ohms or Volts/Ampere
• R = V/I, where V is potential difference and l is current.
• Conductors offer very little resistance
  • Examples include silver, copper, gold, and aluminum.
• Insulators present high resistance
  • Examples include rubber, paper, glass, wood, and plastic
• Semiconductors have properties between insulators and conductors
  • For example, silicon and germanium.
  • Pure semiconductors at very low temperatures act like insulators
  • Increasing the temperature breaks cohesive bonds, creating free electric charges

Resistance and Resistivity

• An object's resistance depends on its shape and material.
• Electric resistance (R) is directly proportional to length (l) and inversely proportional to cross-sectional area (A).
• Resistivity (ρ) is an intrinsic material property, independent of shape or size
  • Measured in Ωm (ohm-meters)
• Conductivity (σ) is the reciprocal of resistivity
  • Measured in Ω⁻¹m⁻¹
  • The higher the resistivity, the lower the conductivity
• Formulas:
  • R = ρ(l/A)
  • R = l/(σA)

Capacitance

• Storing electric charges is capacitance
• It is the ratio of stored charge (Q) to the potential difference (ΔV)
  • Opposes voltage change
• Measured in Farads (Coulomb/Volt)
• C = Q/AV
• Capacitors consist of two parallel plates separated by a distance d, with an area A, and an insulator with permittivity ɛ.
• C = εA/d
• Permittivity is measured in Farads/meter
  • Indicates how a material stores electric energy.

Inductance

• Inductors, also called coils, store energy in a magnetic field when current flows, opposing current change.
• Inductance: the magnetic field flux (φ) generated in the core of an inductor
  • per unit current flowed.
• Measured in Henrys or Weber/Ampere
  • L = φ / I
• For an inductor of length l, cross-section A, N turns, and permeability µ,
  • L = (µN²A) / l
• Permeability has units of H/m, indicating a material's ability to pass magnetic fields

Impedance

• Impedance is the total opposition to alternating current flow in an AC circuit, measured in ohms
  • Resulting from resistance, inductance, or capasitance
• In a DC circuit, impedance is simply resistance (R), while in an AC circuit, it is denoted as “Z”.
• Z = V/I, where V and I are RMS values
• RMS is the value of direct current or voltage that produces the same power dissipation in a resistive load

Series and Parallel Circuits

• Circuit components can be connected in series, parallel, or a combination of both

Impedance Summary

Series and Parallel Resistors

• For two resistors in parallel:
  • 1/R = 1/R₁ + 1/R₂ (True);
  • R = (R₁R₂) / (R₁ + R₂) (True)

Semiconductors

• Germanium (Ge) and silicon (Si) are common semiconductors used for electronic devices.
• They have 4 electrons in their outermost shell
• Covalent bonding, strengthens between atoms by sharing electrons
• Each atom shares with 4 surrounding atoms, completing the outer shell with 8 electrons
• Shell K = 2, L = 8, M = 18, N = 32, O = 50, and P = 72, are electronic capacity

Intrinsic and Extrinsic SC

• Intrinsic Semiconductor: A very pure semiconductor with no impurities.
• Extrinsic Semiconductor: A semiconductor subjected to doping.
  • Doping: Adding small amounts of specific impurities to modify conductivity.

PN-Junction

• SC bonds holding electrons mean a SC does no carry a current
• Breaking bonds creates free electrons or holes, and therefore carries a current
• N-type: Doping with a five valence electrons impurity
• P-type: Doping with a three valence electrons impurity
• Current conduction results from an abundance of electrons in the N-type SC or electrons in the bonds (holes) in the P-type SC (i.e., un-completed bonds)

PN-Junction

• PN - junction (diode): is created by joining two semiconductor material types (P and N – types).
• Recombination of electrons and holes of N- and P-types creates a "depletion region" in the middle, acting like an insulator.

Forward Bias

• The P-type is connected to the positive terminal of the voltage potential, and the N-type is connected to the negative terminal of the voltage potential
• This causes the electrons in the N-type material, and the holes in the P-type material towards the middle boundary, which reduces the width of the depletion region
• The recombination is fast, continuous and concentrated in a small region
• With sufficient applied voltage, the depletion region's resistance becomes negligible
• If forward biased, the PN junction conducts current

Reverse Bias

• In reverse bias, the P-type voltage terminal is connected to negative, and the N-type voltage terminal is connected to positive.
• The withdrawal of electrons and fading the holes create a resistive and thick depletion region, if the applied voltage becomes larger.
  • There is higher resistance and no current
• The PN junction does not conduct current if reversed biased.

Light-Emitting Diodes (LEDs)

• A light-emitting diode (LED) is a PN-junction that emits light when forward biased and current flows through it.
• Electrons and holes recombine if forward biased, so that there is an emitted energy that is material dependent so the color depends used in the semiconducting element.
• Standard Si and Ge diodes dissipate energy as heat without light production

Photoresistors

• It is light sensitive semiconductor cadmium sulfide (CdS) or lead sulfide (PbS).
• Absorbed incident light photons are absorbed by the sensitive material.
• Covalent bands create free charge carries such as electrons, so that the conductivity of the material increases, and so that there is lower resistance
• The less resistance is determined by the more light

Cell Membrane

• Is a thin flexible barrier separating the cytoplasm from the external environment
• It controls what enters and exits.
• It is a dynamic structure with moving and interacting components, not rigid and fixed
• Lipid Bilayer: Is a double layer of lipids (fats) called the phospholipid bilayer
• Phospholipids have a hydrophilic head and two hydrophobic tails.
• The heads face inwards, and the tails face outwards
• Proteins: has diverse functions that are embedded within the lipid bilayer
  • Moves substances across the membrane by transport proteins
  • Receives signals by receptor proteins.
  • Catalyzes chemical reactions by enzymes
  • Provides support and shape by structural proteins.

Membrane Transport

• Passive transport - moves through tiny pores with a channel protein assistant, but no energy is needed
• Active transport - uses a carrier protein with energy

Passive Transport

• Hydrophobic molecules small steroids or lipids diffuse through cell membrane pores because they dislike water. This is called Simple diffusion
• Tiny non-polar particles, such as non-polar solute molecules as alcohol, use Osmosis
• Large polar/ionic molecules, such as glucose or ions, use a protein as facilitator

Active transport

• The sodium-potassium pump uses energy from transporting active carrier protein
• It moves 3 Na+ ions out and 2 K+ ions in, and consumes one ATP, and controls the Na+/K+ ions concentrations
• Sodium/Potassium determines the volume, membrane potential, and nerve/muscle impulses

Active Transport

• The pump mechanism:
  • Combines intraceulluar 3Na+ ions so that ATP binds to release ADP to cause phosphorylation
  • Protein is changed to release the Na+ ions to the outside
  • The K+ ions binds extra-cellular to cause dephosphorylation
  • Original protein restores to release K+ to the cell

Membrane Potential

• It is the voltage difference across the cell membrane from the different ion concentrations, that are present between the outside and the side.
• A cell membrane has an inner negative potential.

Biological Cells as Capacitors

• There are differences in the positive and negative concentrations of cell and outside, so that the cell membrane works acts as a capacitor and there are charge types.
• The cell membrane potential difference: can be measured with two probes, connected to the extra/intracellular fluid, filled with solution on a glass tube
• The measure of the cell membrane potential is about -70mv

Structure of a Neuron

• There is a body, dendrites and axon
• Cell Body or Soma: The nucleus, mitochondria production of energy, houses organellles, incoming integrates and action of signal decisions
• Dendrites: Collects info from outside with tiny synapses Axon: This is a cablle that passes he neuron’s message, that is sends it’s signals across the neuron

Structure of Neuron

• Myelin Sheath: There is fatty layer that is insulated with the action potent ion with signal transmission. Synapse: It acts as PN junction with a one way direction of conduction

Types of Neurons

• Sensory Neurons
  • Receives information from temperature, pressure, and touch
  • Transmits it to the center nervous system with single axon to cord
• Motor Neurons
  • Carry signals from central nervous system
  • Triggers glands and muscles to relax
  • Short dendrites
• Interneurons
  • Conects sensory and motor neurons with signals

Action Potentials

• Action potentials, control electrical impulses throughout muscle
• Resting State, There are charges particles outside with resting about at -70mV
• High concentration is sodium in the outside, because it is read y to receive the signal trigerring cation

Action Potentials

• There can be a chemical and optical trigger the open of cells in the membrane
• Flood the neuruon with positive charges,
• Voltages rise in neurons with depolarization

All-or-Nothing Explosion

• Rests cell has at -70mv, so with reached 55-mV triggers a even
• The change is sudden, must be reached with -55mV from stimulation

Repolarization & Recovery

• The cells recover back to initial stage with Sodium and Posttasium pumping action.

Propagation

• An action potential occurs
• Propagates down axon
• Triggers opening
• Signals reaches
• Due to Conducation

Synapse Specialization

• Neurons sends signals
• action with neurotransmitters trigger release of neurotransmitter into cell through neurotransmitter and receptors
• Postsynaptic cells, through neurotransmitters can become inhibted

Measuring Impedance

• Examnes exist of methods of measuring impedance

Bio-Impedance

• Body through electrical, but with minimal damage, has impedance
• Weak current, but there si no damage
• Fats has high lipid contents, so they are less resistance.
• Mucle has electrocytes, making ir less restitance, higher water contents
• The the frequences with AC, are important to information

Bio-Impedance

• The fluids outside cells are more resistive with certain tissues, while the phospolipid bilayer of cells are capacitors
• Has low resistance at high frequencies with the extracellular fluid The tissue through electrrical flow
• Fluid around cels are at low frequences the mebranes are at high frequency

Bio-Impedance Applications

• At different frequences measuring the body impedance to have bioimpecance-spectroscopy
• For example:
• Estimate for water, muscle, inBody mass The monitoring of fluid distribution with well cells.

Bio-Impedance For Malignant

• To distinguish tumor tissues or maligniticy through water and structures, as with these factors affect cells.

Bio-Impedance In Respiratory Monitors

• Used in Respritory rate monitor (RRM)
• Measuring the breathing of someoen physically
• Elctrodes is current passes
• Impedance change as body changes
• Relfects path of breathing

Measuring Response

• Measuring the human reaction to the human.

Pulse 0ximeter

• It’s measuring blood oxygen saturation

Pulse Oximeter

• Distinct red and infared weavelengthd passes through it
• Absorption based on 0,HB toHB . Calculate the ratio betwen it Counting pressure

Measuring Electrical Pulses,

• Elctricaul pulses with human body example

Exlectroencephalography (EEG)

• Using electrical activity with the scalp
• Electrode placement
• Detectable on equipmets
• Signals measure to find patternds for function to diagnose for therapy.

Electrongmyogrpahy (EMG)

. With muscle signals assess and conditions diagnose With skin and needles can help speed a=p signals.

Electrocardiogram

• Involve electrical movement of heart.
• Electrodes measure the signal, with blood vessel diagnostics
• P, QRS, and T indicate heat'ys electrical stages

Electrocariogram

• With more detaild use it

Sinus and Pulse Pathwasus

• Pathway that allows top, bottom of the sinus is node,

Electrical pathaway Is a sinus made through the atriventacular.

Cardiac Issues

• Auralic contraction

Measured ECGS are pulses

Diagoise with cardio pulses that change directions for dioganesws

Electricity For Stimulations

Through stimulationd evicfes and areas stimulate body

Electrical Devices