The Heart

Question 1

Cardiac muscle cells - terminology (3)

work together “functional syncytium”

Answer 1

Intercalated discs
Desmosomes - hold discs together
Gap junctions - ion exchange. Depolarisation of adjacent cells occurs here.

Question 2

Cardiac conduction system/ nodal system

• no nerve activity required to start contraction

Answer 2

"automaticity" or "autorhythmicity"
Sinoatrial (SA) node
Atrioventricular (AV) node
AV bundle/ bundle of His
Purkinje fibres

Question 3

moderator band

Answer 3

Some branches leave the Bundle of His to go to the papillary muscles of the R ventricle via the moderator band.

Question 4

P QRS T wave

Answer 4

P - depolarisation of atria, and thus contraction of the atria (atrial systole)
QRS - appears as ventricles depolarise, and thus contraction of the ventricles. Atrial depolarisation also occurs here but it is masked.
T - ventricular repolarisation

Question 5

Cell membrane action potential (3 stages)

Answer 5

1. Rapid Depolarization (Na+ entry). Fast Na+ channels, only open for few milliseconds.
2. The Plateau (Ca2+ entry)
3. Repolarization (K+ loss)

Question 6

Resting membrane potential of cardiac cell

Answer 6

-90mV

Question 7

what joins cardiac cells together?

Answer 7

intercalated discs, which are held together by desmosomes. Gap junctions in intercalated discs allow movement of ions.

Question 8

what is a syncytium?

Answer 8

a functional unit of interconnected cells (as seen in cardiac tissue)

Question 9

what is automaticity?

Answer 9

the ability to start a contraction without a nerve impulse (cardiac cells)

Question 10

Elements of the conducting system

Answer 10

• Sinoatrial (SA) node, located in wall of right
• Atrioventricular node (AV), located at junction between atria and ventricles.
• Conducting cells
• AV bundle and the bundle branches
• Purkinje fibers, which distribute the stimulus to the ventricular myocardium.

Question 11

How are action potentials transmitted from auto rhythmical cells? (SA, AV Nodes, bundle of His, Purkinje fibres), etc?

Answer 11

Via gap junctions in the intercalated discs. Signal goes from the authorhythmical cell to the contractile cardiac cell.

Question 12

what is the functional contracting unit in a muscle?

Answer 12

sacromere

Question 13

diastolic phase - what is it?

Answer 13

The filling of the ventricles as the ventricles relax, and the pressure drops because it has pumped blood out

Question 14

What are the lubb / dub sounds?

Answer 14

Lubb - atrio-ventricular valves closing

Dub - semi-lunar valves closing