Cardiac Co-ordination

Question 1

What triggers contraction of cardiac muscles?

Answer 1

Depolarisation of plasma membrane.

Question 2

What allows action potentials to travel from one cell to another?

Answer 2

Gap junctions - interconnect myocardial cells.

Question 3

Where does initial depolarisation arise?

Answer 3

Sino actuarial node - located in right atrium near entrance of superior vena cava.

Question 4

Where does the depolarisation then spread to after passing SA node?

Answer 4

Throughout atria and then into and throughout ventricles.

Question 5

What is the SA node normally referred as?

Answer 5

Pacemaker - depolarisation of SA node generates the action potential that leads to depolarisation of all other cardiac muscle cells.

Question 6

What does the discharge of SA node determine?

Answer 6

Heart rate.

Question 7

What wall of the heart does the action potential from SA node spread throughout?

Answer 7

Myocardium.

Question 8

Where is depolarisation first spread at?

Answer 8

Muscle cells of the atria - contraction rapid - right and left atria contract at the same time

Question 9

What is the link between atrial depolarisation and ventricular depolarisation?

Answer 9

Atrioventricular node - portion of the conducting system - located at the base of the right atrium.

Question 10

What is the action potential conducted rapidly through from the SA to the AV node?

Answer 10

Internodal pathways.

Question 11

What is the important characteristic of the AV node?

Answer 11

Elongated - propagation of action potential through the AV node is relatively slow - this allows atrial contraction to be completed before ventricular excitation occurs.

Question 12

After the AV nodes becomes excited where does the action potential progress to?

Answer 12

Down the inter ventricular septum.

Question 13

What does the inter ventricular septum have?

Answer 13

Conducting-system fibres called bundle of hIS.

Question 14

What does the AV node and bundle of His constitute?

Answer 14

The only electrical connection between the atria and ventricles.

Question 15

What does the bundle of His divide into?

Answer 15

Right and left bundle branches - conducting fibres that separate at the bottom of the heart and enter the walls of both ventricles.

Question 16

What are Purkinje fibres?

Answer 16

Large-diameter conducting cells that rapidly distribute the impulse throughout much of the ventricles.
Purkinje fibres make contact with ventricular myocardial cells, which spread the action potential throughout the rest of the ventricles.

Question 17

What do the fibres in turn make contact with?

Answer 17

Purkinje fibres.

Question 18

What does rapid conduction along the Purkinje fibres and the diffuse distribution of these fibres cause?

Answer 18

Depolarisation of all right and left ventricular cells to occur nearly simultaneously and ensure a single coordinated contraction.

Question 19

Where do the bundle branches run through?

Answer 19

The whole length of the inter ventricular septum.

Question 20

What do purkinje fibres not have?

Answer 20

Contractile units

Question 21

What do purkinje fibres have?

Answer 21

Lots of mitochondria and gap junctions