Physiology: cardiac conduction

Question 1

where does depolarisation begin in sinus rhythm

Answer 1

the SA node

Question 2

what kind of cells does the SA node contain

Answer 2

pacemaker cells

Question 3

describe the action of the SA node pacemaker cells

Answer 3

fire spontaneously without an external stimulus and have short refractory periods

Question 4

describe where the depolarisation travels after the SA node (4)

Answer 4

AV node => bundle of His => bundle branches => Purkinje fibres

Question 5

describe the resting potential of the SA node cells

Answer 5

they have no stable resting potential

Question 6

what type of junction allows the action potentials to travel between cells

Answer 6

gap junctions

Question 7

describe what happens to conduction velocity at the AV node and why

Answer 7

conduction velocity slows to allow ventricles time to fill

Question 8

if the SA node fails to fire spontaneously, where else in the heart are there pacemaker cells that can act as back-up (3)

Answer 8

Plan B = other parts of atria
Plan C = AV node
Plan D = His-Purkinje fibres