Myocite action potential

Question 1

repetitive cardiac contraction is essential to life and depends on the inherent contractile properties, i.e. the _______ of cardiac myocytes

Answer 1

autorhythmicity

Question 2

a cardiac muscle fibre contract when what is transmitted along what

Answer 2

when an action potential is transmitted along its plasma membrane

Question 3

what are the 2 types of cardiac myocytes

Answer 3

a ventricular myocyte (non-pacemaker) and a pacemaker myocyte

Question 4

define ‘action potential’

Answer 4

the transient depolarisation of a cell followed by by repolarisation, as a result of movement of ions across its cell membrane via ion channels

Question 5

at rest, the membrane has a low permeability to which 2 ions and a higher permeability to which ion

Answer 5

low permeability - Ca and Na

higher permeability - K

Question 6

As it has a higher permeability to this ion at rest, the resting membrane potential is primarily dependent on the __ concentration gradient and remains near the __ equilibrium potential (about ___mV)

Answer 6

K+
K+
-90

Question 7

an action potential is initiated when the membrane is _____ (made

Answer 7

depolarised

threshold

Question 8

the depolarisation phase is caused by rapid transient entry of ___ through ___-___ ___ channels into the myocyte causing an increase membrane permeability to ___. Simultaneously, membrane permeability to ___ falls causing the membrane potential to move away from the __ equilibrium potential and towards the ___ equilibrium potential (___mV), resulting in a rapid _________.

Answer 8

Na+
voltage-gated Na+
Na+
K+
K+
Na+
\+60
upstroke

Question 9

At the end of the upstroke, membrane permeability to ___ returns to its resting value - why is this? This causes the membrane potential to decay slowly over about 0.25s resulting in the _____ phase.

Answer 9

Na+
due to inactivation of the Na+ channels
Plateau

Question 10

The plateau phase is primarily due to the slow influx of ___ via what type of channels? These activates relatively slowly/ quickly when the membrane potential reaches about 40mV, resulting in an increase membrane permability to ____. Ca+ entry into the cell during this phase is vital for _______ ____

Answer 10

Ca+
Long lasting voltage-gated Ca+ channels (L type) 
Slowly
Ca+
Muscle contraction

Question 11

At the end of the plateau, which channels open causing an increased membrane permeability to ___ while the ___ permeability decreases. The membrane potential returns to its resting level, this phase is called the _____ phase.

Answer 11

Voltage-gated K+ channels
K+
Ca+
Repolarisation