Electricity in the Body

Question 1

What is an action potential?

Answer 1

A brief electrical charge that travels down the axon of a neuron

Question 2

What is the resting membrane potential?

Answer 2

The difference in charge between the relatively negative intra-cellular environment and the extra cellular environment (the cell is polarised)

Question 3

Usually, what are the relative concentrations of sodium and potassium inside and outside cells?

Answer 3

High sodium concentration outside cells and low inside cells

Low potassium concentration outside cells and high inside cells

Question 4

What are the stages of a non-cardiac action potential?

Answer 4

Resting state (normal, polarised state), depolarisation and repolarisation

Question 5

What happens during depolarisation (non-cardiac)?

Answer 5

Voltage gated sodium channels allow sodium to enter the cell, equalising the charge on either side of the cell membrane and depolarising it

Question 6

What happens during repolarisation (non-cardiac)?

Answer 6

Potassium moves out of the cell via voltage gated potassium channels, restoring the resting membrane potential and repolarising the cell membrane

Question 7

After repolarisation, how are the correct intracellular and extracellular concentrations of sodium and potassium restored?

Answer 7

The sodium potassium antiporter transfers 3 sodium ions out of the cell and 2 potassium ions into the cell with every phosphorylation by ATP

Question 8

What are the components (in order) of the conduction system of the heart?

Answer 8

Sinoatrial node, Atrioventricular node, Bundle of HIS, Left and Right Bundle Branches, Purkinje Fibres

Question 9

Which cells in the heart generate action potentials?

Answer 9

Pacemaker cells

Question 10

How is synchrony maintained between cardiac myocytes?

Answer 10

Adjacent cardiac myocytes are connected by gap junctions

Question 11

What are the stages of cardiac action potential?

Answer 11

Depolarisation (Phase 0), Slow Repolarisation (Phase 1), Plateau Phase (Phase 2), Repolarisation (Phase 3)

Question 12

What causes depolarisation phase (cardiac)?

Answer 12

The rapid entry of sodium into the cardiac myocyte

Question 13

What causes the slow repolarisation phase (cardiac)?

Answer 13

The slow exit of potassium ions from the myocyte

Question 14

What causes the plateau phase (cardiac)?

Answer 14

The entry of calcium into the myocyte

Question 15

What causes the repolarisation phase (cardiac)?

Answer 15

The rapid exit of potassium from the myocyte

Question 16

What are the waves in an ECG?

Answer 16

P, Q, R, S and T waves

Question 17

What does the P wave represent in an ECG?

Answer 17

Atrial depolarisation

Question 18

What does the Q wave represent in an ECG?

Answer 18

Excitation of the interventricular septum (The beginning of ventricular depolarisation)

Question 19

What does the R wave represent in an ECG?

Answer 19

The spreading of excitation through right and left ventricular myocytes

Question 20

What does the S wave represent in an ECG?

Answer 20

Completion of ventricular depolarisation (Basal areas of interventricular septum)

Question 21

What does the T wave represent in an ECG?

Answer 21

Rapid late repolarisation of ventricular myocardium

Question 22

What can electric shocks cause?

Answer 22

Muscle contractions and pain (may result in patient being unable to let go of the source)
- Inability to breathe if respiratory muscles are force to continuously contract
Cardiac arrest
- Patient goes from normal sinus rhythm into arrhythmia (most commonly ventricular fibrillation)
Burns (at entry and exit site of current)

Question 23

What is the course of action for electrocution first aid?

Answer 23

1. Check for safety
   - You cannot assist if you are also getting electrocuted
2. Shout for help
3. Turn of electricity at the mains
4. Commence CPR if required
   - Use defibrillator if required to reset heart rhythm
5. Attend to burns once patient is able to breathe on their own and heartbeat is restored

Question 24

How does a defibrillator work?

Answer 24

Arrests fibrillation of heart muscle by applying electric shock across the chest, depolarising cardiac myocytes and allowing normal rhythm to return

Question 25

What is diathermy?

Answer 25

A high-frequency alternating current for the purpose of cutting of tissue/cauterising blood vessels

Question 26

What is the function of a transcutaneous electrical nerve stimulation (TENS) machine?

Answer 26

To assist in alleviating labour pains by blocking/interfering with the transmission of sensory information by stimulating sensory nerves