Intro to Electrophysiology Flashcards
(22 cards)
What is electrical current?
Movement of charge from one place to another
What are volts?
Electrical pressure potential difference
What is resistance?
‘Push back’ of the current within the conductor
What is Ohm’s law?
I=V/R
i.e. electrical current is determined by the electrical potential difference and the resistance of the conductor
What is bioelectrical current generated by?
Movement of electrically charged ions which are moving according to potential difference
Why are bioelectrical currents small?
Cells have high resistance and ions have mass
What is standing potential and how is it measured?
Electrical charge of the whole eye
Measured using EOG
Why is the cornea more positive than the posterior pole?
Large potential difference across the RPE
What is the standing potential of the eye?
2-20mv
How is an EOG measured?
Measures the voltage swing when the eyes are moving right to left
What are evoked potentials?
Specific cellular responses to stimulation
What does an ERG measure?
Retinal activity
What does a VEP measure?
V1 activity
Where are electrodes placed for an ERG?
Forehead (earth)
Outer canthus (reference)
Cornea (active)
What does an ERG waveform depend on?
Stimulus duration
Stimulus intensity
Stimulus wavelength
Retinal adaptation (if photopic etc)
What are the components of an ERG wave, and which part of the retina do they correspond to?
Early receptor potential
A-wave: Photoreceptors
B-wave: Bipolars
PhNR (Photopic Negative Response): Ganglion cells
C-wave
D-wave: Off response
Where can noise come from?
Mains hum (50hz)
Random electrical noise
Unwanted biological noise
What are some noise solutions?
Differential amplification
Averaging responses
Artefact reject
Electronic filters
What is differential amplification?
Subtract the reference results from the active results
i.e. (signal+noise) - (noise) = signal
What is averaging responses?
Taking multiple readings and finding the average will show what is the signal and what is noise (noise will be random every time but signal should be consistent)
What is artefact reject?
Computerised filtering of responses above a certain voltage which will not be part of the signal (e.g. blinking has v high voltage)
What are electronic filters?
Filtering out frequencies outside a particular range (between 1-1000hZ)
Can also set a notch filter to eliminate known noise frequencies (e.g. mains hum @ 50hz)
