Module 3 - Bioelectricity Flashcards
Who is credited with the discovery of bioelectricity and when?
Luigi Galvani in 1700s
Describe galvanization
Galvani applied electric current to dissected frog legs, causing them to twitch
Describe the public experiment conducted by Giovanni Aldini (Galvani’s nephew).
Used body of executed prisoner
Minutes after execution, Aldini performed galvanization on the body, causing movements of the jaw, eyes, right hand and legs
What is electrophysiology?
Use of equipment to study bioelectricity
Who developed the differential rheotome?
Julius Bernstein in 1902
What is the differential rheotome?
Instrument used to sample membrane voltage in microsecond scale
What are the three general paradigms for electrophysiological recording?
Extracellular recording
Intracellular sharp electrodes
Whole-cell patch electrodes
What is extracellular recording?
Records voltage/ion fluxes along the outside surface of a cell
How many electrodes can be used in extracellular recording?
Single or multiple
What are intracellular sharp electrodes?
Record voltage/ion fluxes across the cell membrane
How many intracellular sharp electrodes can be used?
Single or double
What are whole-cell patch electrodes?
Record voltage/ion fluxes across the cell membrane
What is a benefit to whole-cell patch electrodes?
Large access into cell, allowing you to change the intracellular saline
What did protein engineers combine to create GCaMP calcium indicators?
- GFP
- The Ca2+ sensor protein calmodulin (CaM)
- The M13 alpha helix of the muscle protein myosin light chain kinase
What happens to GCaMP when Ca2+ levels rise?
Increases fluorescence
Describe how the GCaMP calcium indicator works.
APs cause Ca2+ influx
Ca2+ activates CaM
CaM binds the M13 helix
This pulls on the GFP protein, changing its structure
Increased GFP fluorescence
What is current?
Movement of charged particles through a conductor/resistor
What is the symbol for current?
I
What are the units for currents?
Amperes (A)
What are the charged particles that move through metal wires?
Electrons
What are charged particles that move through aqueous solutions?
Cations and anions
What unit are charges counted/measured in?
Coulombs (C)
What is the energy for charge movement?
Voltage
State Ohm’s Law and define the variables
I = V*G
I = current
V = electrical potential energy
G = conductance
True or false, a conductor is also a resistor?
True
What is the equation that shows the relationship between resistance and conductance?
G = 1/R
Outline the relationship between a conductor and a resistor.
A good conductor (gold) makes a bad resistance
A good resistor makes a bad conductor (rubber)
State Ohm’s law with resistance
I = V/R
What happens when a voltage is applied across a conductor/resistor?
A current is produced
Where does membrane voltage originate from in excitable cells?
From ion concentration gradients across the cell membrane
What are the conductors/resistors in cells?
Ion channels across the cell membrane
Is the cytoplasm a conductor?
Yes
Define a capacitor.
A capacitor consists of two conductive plates separated by an insulator
What is the capacitor of cells?
Cell membrane
What are the two conductive plates of the cell’s capacitor?
cytoplasmic and extracellular salines
What is the insulator of the cell’s capacitor?
phospholipid bilayer
Why must the insulator of a capacitor be thin?
So the charges can “sense” each other across the plates.
What happens at a capacitor when a voltage is applied?
Opposite charges accumulate along opposite plates
A current results from the repulsion/attraction of ions across the membrane
Applied charge accumulate until energy in capacitor matches the applied voltage
How are capacitors different than batteries.
Capacitors can hold and applied voltage and thus act as a voltage source, but cannot generate voltages, only borrow
Give the equation for the capacitance of a capacitor and define the variables.
C = q/V
C = capacitance
q = charge
V = electrical potential energy
What determines capacitance?
Properties of the insulator
Conductive plates
Surface area of capacitor
