Electrical Conductiom Of The Heart

Question 1

What is the annulus fibrosis

Answer 1

4 interconnected rings of connective tissue between atria and ventricles
Acts as an electrical insulator

Question 2

What are cardiac myocytes

Answer 2

A contractile excitable cardiac cell

Question 3

Why does the SA drive the rhythm of the heart

Answer 3

The SAN can generate an action potential spontaneously
Depolarisation occurs the quickest at the SAN

Question 4

What are autorhythmic cells and some examples

Answer 4

They spontaneously generate an action potential
Examples:
SAN
AVN
Bundle of His
Purkynje fibres

Question 5

What happens at each phase of action potential is cardiac myocutes

Answer 5

Phase 0:
Rapid influx of Na+ channels
Normal K+ channels are open

Phase 1:
VG Na+ channels shut very quickly
VG K+ channels open to remove K+

Phase 2: (membrane potential is stable as K+ leaving and Ca entering)
Ca2+ VG channels open

Phase 3:
Ca2+ channels close
VG K+ channels are still open

Phase 4:
VG K+ channels close

Question 6

What would happen if the SAN stops working

Answer 6

The AVN would eventually spontaneously depolarise but at a slower rate

Question 7

Why does the parasympathetic nervous system not influence ventricular muscle cells

Answer 7

Very few ventricular muscle cells have a parasympathetic nervous supoly

Question 8

What effect does the sympathetic nervous system have n the cardio myocytes

Answer 8

The SNS doesn’t just release the neurotransmitter at the nodes but also all over the muscle
Results in taller, shorter and quicker action potentials
So quicker more forceful contraction

Question 9

What effect does the sympathetic NS have on the velocity of the action potential and the refractory period of the AVN?

Answer 9

Increases velocity, shortens AV delay
Shorter refractory period
Faster depolarisation

Question 10

What effect does the parasympathetic NS have on the velocity of the action potential and the refractory period of the AVN?

Answer 10

Decreases velocity (longer AV delay)
Longer refractory period
Slower depolarisation

Question 11

How does the sympathetic NS increase HR

Answer 11

Noripherine acts on B adrenergic receptor
Speeds up ion channel changes
Pacemaker cells reach threshold value quicker
So shorter interval between heartbeat

Question 12

How does the parasympathetic NS slow down heart rate

Answer 12

Acetylcholine activates muscarinic cholinergenic receptors
Slows down ion channel changes
Pacemaker cells take longer to reach threshold value so longer interval between heart beat