Pacemaker action potential

Question 1

are the action potential characteristics of the pacemaker the same as those of the cardiac myocyte?

Answer 1

no

Question 2

some cells within the specialised conduction system have the ability to act as pacemakers and spontaneously initiate action potentials, whereas ordinary cardiac muscle cells do not under normal conditions. these pacemaker cells make up the ____ ____

Answer 2

SA node

Question 3

during the resting phase the membrane potential is more/less negative than that of ventricular muscle fibres and is around ___ to ___ mV

Answer 3

negative

• 55
• 60

Question 4

during the resting phase, a progressive decrease in membrane permeability to ___ results in fewer ___ moving out of the cells, and a slight increase in ___ permeability causes a slow influx of ___ (‘____’ current) contributing towards hyperpolarisation/depolarisation. Around this time, a small rise in ___ conductance into the cells via __ type __ channels (transient_ which open very briefly causing the membrane potential to rise gradually towards ______ potential (__mV). This unstable resting potential is called the ________ potential.

Answer 4

K+
K+ 
Na+
Na+ 
funny
depolarisation
Ca2+
T
Ca2+
threshold
-40
pacemaker

Question 5

as the potential reaches threshold voltage, many slow long lasting ___ (__ type) channels begin to open, and the slow influx of ___ into the cell is primary responsible for the _______ phase of the action potential.

Answer 5

Ca2+
L
Ca2+
depolarisation

Question 6

Repolarisation phase;

voltage gated ___ (__ type) channels become inactivated together with the opening of a large number of voltage gated ___ channels, causing diffusion of ___ out of the fibre

Answer 6

Ca2+
L
K+
K+

Question 7

Hyperpolarisation phase;

The ___ channels remain open for a few tenths of a second carrying a great excess of positive/negative potassium ions out of the fibre resulting in an excess positivity/negativity inside the fibre. This is called ______ and the membrane potential reaches ___ to ___ mV.

What happens after the resting membrane potential is re-established?

Answer 7

K+
Positive
Negativity
Hyperpolarisation
-55
-60
Spontaneous production of another pacemaker potential starts the generation of the next action potential.