eLFH - Excitable Tissues and Biological Potentials

Question 1

Examples of biological potentials

Answer 1

Electrocardiogram (ECG) - cardiac

Electroencephalogram (EEG) - brain

Electromyogram (EMG) - muscle

Question 2

Composition of biological potentials

Answer 2

Biological potentials are composed of sine waves with different frequencies and phases

Question 3

Analysis method for potentials

Answer 3

Fourier analysis

Question 4

Fourier analysis

Answer 4

Breaks composite potential wave into its simpler components

Question 5

Two major factors which determine size of potential that is measured

Answer 5

Mass of the excitable tissue

Amount of tissue separating the recording electrode from the excitable tissue

Question 6

Voltage of measured ECG vs membrane potential

Answer 6

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

Question 7

Frequency of Delta brain waves

Answer 7

3 Hz

Question 8

Frequency of Beta brain waves

Answer 8

12 - 25 Hz

Question 9

Three main parts of a recording system

Answer 9

Electrodes
Amplifier
Display unit

Question 10

Construction of non-invasive electrodes

Answer 10

Silver electrode in contact with silver chloride and a conductive gel. Surrounded by adhesive disc

Question 11

Issues with non-invasive electrodes which modern electrode construction (previous flashcard) aims to avoid

Answer 11

Loss of skin contact

Polarisation of electrode

Moisture trapped between electrode and skin can cause battery effect - recording system generates potential

Question 12

Clinical application of stimulating biological potential

Answer 12

Defibrillator
ECT
Nerve stimulators
Pacemakers
Deep brain stimulators

Question 13

Energy delivered by defibrillators

Answer 13

Energy delivered in joules

Energy is directly proportional to voltage applied and the charge stored across capacitor plates

Question 14

Function of inductor in defibrillator circuit

Answer 14

Modulates shape of the current delivered to patient

Question 15

Mechanism of defibrillation

Answer 15

Current delivered causes direct stimulation of myocardium followed by refractory period

After refractory period hopefully normal cardiac rhythm will resume

Question 16

At which point in rhythm does synchronised cardioversion synch with

Answer 16

R wave

Question 17

Method to reduce impedance when pads applied

Answer 17

Use of gel pads on skin

Question 18

Needle nerve stimulator vs peripheral nerve stimulator

Answer 18

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

Question 19

Use of needle nerve stimulator

Answer 19

Regional anaesthesia to avoid intraneural injection

Question 20

Current used for needle nerve stimulator

Answer 20

2 mA

If muscle contraction even with very low current (< 0.3 mA) then suggests likely intraneural so don’t inject

Question 21

Current used for peripheral nerve stimulator

Answer 21

80 mA

Question 22

Frequency used for peripheral nerve stimulator

Answer 22

1 - 10 Hz

Question 23

Function of deep brain stimulators

Answer 23

Stimulating electrode placed in close proximity to centres that regulate movement e.g. thalamus

Delivers set current to stimulate relevant brain area