Chapter 4

• electron

  = amber (fossilized tree resin)

  -> if rub amber with wool: electrical charge (static)
• What is electricity?

  Flow of electric charge + a natural phenomenon
• What is a lightning?

  Electrical discharge of a potential difference in the atmosphere
• What signals does the human nervous system use to communicate?

  electrical signals
• Are some animals able to generate electricity?

  Yes, some fish are capable of generating electricity (e.g. eels)
• WHat is charge (in electric charge)?

  a property of matter (just like mass, volume, or density)

  ->Just as you can quantify how much mass sth has, can measure how much charge it has
• What is the key concept with charge?

  can come in 2 types:

  • positive (+) or
  • negative (-)
• Physical basis of electrical charge

  1. world consists of matter
  2. matter consists of molecules (e.g. Water, H2O)
  3. molecules consist of elements (hydrogen (H), oxygen (O)
  4. atoms = smallest particle of an element that has the properties of that element
• What do atoms consist of?

  • Protons (+) & neutrons (0) -> inside the cneter (nucleus) of the atom
  • Electrons (-) outside nucleus (orbit in electron shells)

  
• What are ions?

  charged atoms

  2 types:

  • anions
  • cations
• What are anions?

  Negatively charged ions (e.g. Cl-)

  -> have surplus of electrons
• What are cations?


  Positively charged ions (e.g. Na+)

  -> have shortage of electrons
• What is the triboelectric effect?

  Electrification

  -> rubbing wool against amber causes negatively charged electrons to “jump” from the wool to the amber

  • amber gets surplus (= more) of electrons (so: becomes negatively charged)
  • wool gets shortage of electrons (so: becomes positively charged)
• What is the potential differnece or voltage?

  = (relative) difference in charge between e.g. wool & amber (when rubbing wool against amber) -> 2 connections needed to measure (e.g. 2 poles on a battery)
• What is the unit of voltage?

  volt
• What is the measurement of voltage?

  Voltmeter
• What is a current & its unit of measurement?

  = an electrical charge that moves

  • unit of measurement: Ampère (A)
• What does the current do?


  Connecting two objects (or two poles within the same object) with different electrical charges:

  1. charge moves from high electron concentration area to low concentration of electrons -> electron flow from - to + = electron current (e.g. from amber - to wool +)
• 2 types of currents:

  • Alternating current (AC) -> home appliances with motors (e.g. vacuum cleaner)
  • Direct current (DC) -> nervous system
• What equipment is necessary to measure electricity in the nervous system?

  • voltometer for potential differences (voltage)
  • ampere for electrical current
  • ALWAYS 2 connections (poles)!!
  • e.g. inside vs outside of cell (over cell membrane)
  • image: electrodes connect to 2 different parts of axon (not same one)

  
• Voltage & Current can also be administered

  
• WHat is an Oscilloscope ?

  measures voltage as function of time
• By a flow of what is the current in the nervous system provided?

  flow of (mostly positive) ions
• What is the ion current?

  ions flow from + to -
• What is Na+?

  sodium ion
• What is K+?

  potassium ion
• What is Cl-?

  chloride ion
• What is Ca2+?

  calcium ion
• What is a key difference between electrons and ions?

  electrones are much faster than ions
• How does ion movement produce electrical charges?

  • diffusion (passive)
  • concentration gradient (passive for specific types of ions -> depends on channels)
  • voltage gradient (difference in charge between 2 locations)
• Diffusion of Water

  = H2O -> hydrogen H+ (positive) + hydroxide OH- (negative)
• Diffusion of Salt

  = Na+ Cl- (sodium chloride)
• What is diffusion?

  = a passive process

  • Na+ binds wiht negative poles (O)
  • Cl- binds with positive poles (H)

  
• What does equilibrium mean?

  = equal number of molecules everywhere
• Concentration gradient & voltage gradient

  here:

  (A) impermeable membrane: equilibrium depends on concentration gradient & type of liquid

  
• Resting potential (potential energy)

  = difference in charge between intracellular & extracellular side ~ -70mV
• Which ions are critical to resting potential?

  1. Cations: Na+ (sodium); K+ (potassium)
  2. Anions: Cl- (Chloride); A- (large protein molecules)
  3. intracellular: more A- & K+
  4. extracellular: more Cl- & Na+
• Resting potential -image

  
• How to maintain resting potential?

  • Channels: allow K+ influx & efflux (passive transport) to balance intracellular A-
  • Gates: prevent influx of Na+
  • Na+/K+ pump: pumps Na+ out of cell & K+ into cell

  
• What are the 2 options to stimulate a neuron?

  1. apply negative charge (voltage)

  • hyperpolarization -> K* efflux or Cl- influx
  • potential difference increases

  2. apply positive charge (voltage)

  • depolarization -> Na+ influx
  • potential difference decreases

  !!both options include graded potentials