Circulatory Sytem - Heart Electrophysiology

Question 1

Electrophysiology

Answer 1

Cardiac cells have a resting membrane potential (rpm)
- dependent on a low permeability of the plasma membrane to sodium to calcium membrane and higher permeability to potassium

Action potential consist of
1 rapid depolarisation
2 early partial depolarisation phase
3 plateau phase ( only cardiac cells)
4 final depolarisation phase

How it works
1 sodium gates open
2 rapid depolarisation
- fast influx of sodium ( more +)
3 sodium gates close and opening of potassium slow efflux
- less positive
4 opening of calcium slow efflux
- balance potassium slow efflux = plateau
- heart still contracting
5 calcium channels close potassium channels stay open
- more negative/ depolarisation
- back to resting potential ready to go again

Question 2

Absolute refractory period

Answer 2

Heart or cardiac cell can not respond to any new stimulus. If some sort of stimulus occur no matter how powerful that stimuli is there is not going to be another contraction of that cardiac cell in that period of time. Prevent the heat from staying fully contracted and not beating

Question 3

The conduction system- overview

Answer 3

Sinoatrial node ( pacemaker)- initiates the electrical signal and sets your heart rate

1. SA node fires
   2 excitation spreads through artrial myocardium
2. Atrioventricular node ( AV node) fires
3. Excitation spreads down AV ventricle
   5 Purkinje fibres distribute excitation through ventricular myocardium

Question 4

The conduction system- Sinoatrial ( SA) node

Answer 4

• modified cardiocytes
• pacemaker initiates each heart beat and determines heart rate
• signals spread throughout atria ( specialised intermodal tracts)
• bachmann’s bundle transmits the signal to left atrium

Question 5

The conduction system - atrioventricular (AV) node

Answer 5

• electrical gateway to the ventricles
• fibrous skeleton- insulator prevents currents from getting to ventricles from any other route

Question 6

The conduction system- atrioventricular (AV ) bundle

Answer 6

• bundle forked into two parts left and right bundle branches
• branches OSS through interventricular septum towards apex

Question 7

The conduction system- purkinje fibres

Answer 7

• nerve like processes spread throughout ventricular myocardium
• signals passes from one cell to another through gap junctions

Question 8

Nerve supply to the heart

Answer 8

Sympathetic never( raise heart rate)
- originates in the lower cervical to upper thoracic segments of the spinal cord
- increase heart rate and contraction strength and dilates coronary arteries to increase myocardial blood flow

Parasympathetic nerves ( slows heart rate)
- pathway begins with nuclei of the vagus nerves in the medulla oblongata
- extends to cardiac plexus and continue to the heart by way of cardiac nerves
- fibres of the right vagus nerve lead to the SA node
- fibres of the left vagus never lead to the AV node
- little or no vagal stimulation of the myocardium

Question 9

Electrocardiogram (ECG)

Answer 9

Detect and amplify and record all action potentials that are generated by nodal and myocardial cells

Recorded electrical signals represent depolarisation and repolarisation

Question 10

Cardiac cycle

Answer 10

One complete contraction and relaxation of all four chambers of the heart

Question 11

Blood pressure and flow

Answer 11

Pressure causes a fluid to flow
Resistance oppresses fluid for

Question 12

Phases of the cardiac cycle - ventricular filling

Answer 12

• during diastole, ventricles explains and pressure drops below GST of the atria
• AV valves open and blood flows onto the ventricles

3 phases
1 rapid ventricular filling
2. Diastasis
3. Artrial

End- diastolic volume
- amount of blood contained in each ventricle at the end of ventricular filling

Question 13

Phases of the cardiac cycle - isovolumetric contraction

Answer 13

• atria repolarise and relax ( for rat is cardiac cycle)
• ventricles depolarise (QRS complex) begin to contract

Isovolumetric - because even though the ventricles contact they do not eject blood

Question 14

Phases of the cardiac cycle - ventricular ejection

Answer 14

Begins when the ventricular pressure exceeds arterial pressure and forces seminar valves to open

Blood spurts out of each ventricle rapidly and then more slowly

End systolic volume- blood left behind around 60 mL

Question 15

Phases of the cardiac cycle - isovolumetric relaxation

Answer 15

Early ventricular diastole
- t wave ends/ ventricles begin to expand

Elastic recoil and expansion causes rapid pressure drop rapidly ( suck blood into the ventricles)

Question 16

Which ion primarily depolarizes the ventricular myocytes leading to contraction?

Answer 16

Sodium ions

Question 17

The T wave on an ECG represents what phase of the cardiac cycle?

Answer 17

Repolarization of the ventricles

Question 18

What does the P wave on an ECG signify?

Answer 18

Atrial depolarisation

Question 19

Which of the following arrhythmias is characterized by a fast and irregular heartbeat

Answer 19

Ventricular fibrillation

Question 20

What is the function of the AV node in the heart’s electrical conduction system

Answer 20

It slows down the electrical impulses to allow the atria to fully contract before the ventricles do

Question 21

What effect does the sympathetic nervous syster have on the heart rate?

Answer 21

It increases the heart rate

Question 22

What is the role of the Sinoatrial (SA) node in the heart’s electrical system?

Answer 22

It initiates the electrical impulses, acting as the heart’s natural pacemaker

Question 23

Where is the SA node located?

Answer 23

Upper right atrium

Question 24

How are electrodes typically placed for a standard 12-lead ECG?

Answer 24

On the chest and limbs

Question 25

What is the end-diastolic volume (EDV?

Answer 25

• B. The amount of blood contained in each ventricle at the end of ventricular filling

Question 26

Waves

Answer 26

P wave - atrial depolarisation
QRS wave- ventricle depolarisation
T wave - ventricle repolarisation