Pacemaker and cardiac conduction

Question 1

What are autorhythmic cells

Answer 1

specialized cells that generate electrical impulses throughout the myocardium

Question 2

How do autorhythmic cells generate action potentials

Answer 2

Undergo slow depolaristaion until threshold is reached

Question 3

Where do these depolarisations occur most rapidly

Answer 3

Sinoatrial node

Question 4

Where is the sinoatrial node located

Answer 4

In the upper wall of the right atrium

Question 5

What controls the rate of depolaristaion

Answer 5

The rate of sodium ion entry

Question 6

Where is the atrioventricular node located

Answer 6

interatrial septum

Question 7

What is the function of the atrioventricular node

Answer 7

Electrical relay from the sinoatrial node, sending impulses through the myocardium towards the apex of the heart, causing the heart to contract and ‘beat’. Can also act as a pacemaker

Question 8

What is the bundle of his

Answer 8

Also known as the common bundle. It is located in the upper portion of the interventricular septum and connects the AV node with the bundle branches. Has an intrinsic rate of 40-60 bpm

Question 9

What are purkinje fibres

Answer 9

Modified myocardio fibres that have less contractile elements , rapidly conduct impulses, last resort when other pacemakers fail

Question 10

Describe the sequence of events that goes into contraction of the heart

Answer 10

1. Source of excitation is normally the SA node
2. Spread of impulse assisted by branching arrangement of the heart muscle fibres
3. Excitation wave spreads through atria
4. There is a delay to the ventricles so that blood is pumped out of the atria

Question 11

What is the anulus fibrosus

Answer 11

outer collar composed of collagen and fibrocartilage

Question 12

What is the function of the anulus fibrosis

Answer 12

Electrically insulates ventricles from atria, allows ventricular filling to complete before the initiation of ventricular systole

Question 13

What are the main functions of the conducting system

Answer 13

• delay impulse transmission between atria and ventricles
• form as the only connection between atria and ventricles
• allow more rapid contraction of action potentials than is possible, enables entire ventricular myocardium to contract simultaneously

Question 14

How do purkinje fibres help with the conducting system

Answer 14

ensures simultaneous contraction, from the apex to the base of the heart

Question 15

What does the long refractory period of the atrioventricular node prevent

Answer 15

Ventricles contracting too fast (atrial fibrillation)

Question 16

Which branch of the autonomic nervous system would reduce the AV node delay

Answer 16

Sympathetic

Question 17

What does the rate of sodium influx in pacemaker cells result in

Answer 17

rate of depolarisation

Question 18

What are some sympathetic actions at the SA node

Answer 18

• release noradrenaline at SA node, increase heart rate

- increase rate of drift to threshold

Question 19

What are some parasympathetic actions at the SA node

Answer 19

• Release acetylcholine at SA node cells to decrease heart rate
• decreases rate of drift to threshold

Question 20

Describe some sympathetic actions on cardiac cells

Answer 20

• B-receptor activation= higher shorter action potentials. Also stronger quicker contractions
• increases Ca2+ entry
• K+ channels open sooner

Question 21

Describe some parasympathetic actions on cardiac cells

Answer 21

• Mainly act on SA and AV nodes
• strong anti-sympathetic action on atrial cells
• SA node= decrease rate
• AV node= slow conduction and lenghtens refractory period

Question 22

Where does the sympathetic innervation to the heart come from

Answer 22

From T2-T4 via mid-cervical and cervico thoracic ganglia to supply SA node+ whole myocardium

Question 23

Where does the parasympathetic innervation to the heart come from

Answer 23

Vagus to supply SA node and atria