eLFH - Excitable Tissues and Biological Potentials Flashcards
Examples of biological potentials
Electrocardiogram (ECG) - cardiac
Electroencephalogram (EEG) - brain
Electromyogram (EMG) - muscle
Composition of biological potentials
Biological potentials are composed of sine waves with different frequencies and phases
Analysis method for potentials
Fourier analysis
Fourier analysis
Breaks composite potential wave into its simpler components
Two major factors which determine size of potential that is measured
Mass of the excitable tissue
Amount of tissue separating the recording electrode from the excitable tissue
Voltage of measured ECG vs membrane potential
Membrane potential is 90 mV negative
Measured ECG is 1-2 mV
This is because of tissue between recording electrode and excitable tissue affecting size of measured potential
Frequency of Delta brain waves
3 Hz
Frequency of Beta brain waves
12 - 25 Hz
Three main parts of a recording system
Electrodes
Amplifier
Display unit
Construction of non-invasive electrodes
Silver electrode in contact with silver chloride and a conductive gel. Surrounded by adhesive disc
Issues with non-invasive electrodes which modern electrode construction (previous flashcard) aims to avoid
Loss of skin contact
Polarisation of electrode
Moisture trapped between electrode and skin can cause battery effect - recording system generates potential
Clinical application of stimulating biological potential
Defibrillator
ECT
Nerve stimulators
Pacemakers
Deep brain stimulators
Energy delivered by defibrillators
Energy delivered in joules
Energy is directly proportional to voltage applied and the charge stored across capacitor plates
Function of inductor in defibrillator circuit
Modulates shape of the current delivered to patient
Mechanism of defibrillation
Current delivered causes direct stimulation of myocardium followed by refractory period
After refractory period hopefully normal cardiac rhythm will resume
At which point in rhythm does synchronised cardioversion synch with
R wave
Method to reduce impedance when pads applied
Use of gel pads on skin
Needle nerve stimulator vs peripheral nerve stimulator
Peripheral nerve stimulator uses electrodes similar to ECG
Needle nerve stimulator current is directly applied to needle tip which is inserted close to neural bundle
Use of needle nerve stimulator
Regional anaesthesia to avoid intraneural injection
Current used for needle nerve stimulator
2 mA
If muscle contraction even with very low current (< 0.3 mA) then suggests likely intraneural so don’t inject
Current used for peripheral nerve stimulator
80 mA
Frequency used for peripheral nerve stimulator
1 - 10 Hz
Function of deep brain stimulators
Stimulating electrode placed in close proximity to centres that regulate movement e.g. thalamus
Delivers set current to stimulate relevant brain area
