Week 16: (B) Pacemaker activity of cardiac autorhythmic cells Flashcards
What is the threshold for cardiac auto rhythmic cells?
-40mV
When an AP in generate by Ca2+ what direction does Na+ move?
higher conc outside cell, enter cell
What does Na+ do to the membrane potential?
causes depolarisation
more positive
What 2 phases can the pacemaker potential be split into?
early and late
What is the early phase of pacemaker potential?
Na+ funny channels (lf) are open
Na+ moves into the cell down its conc gradient
How long are voltage gated channels open?
finite period of time
What happens when Na funny channels begin to close in the early stage of pace maker potential?
- different set of voltage gated ca2+ channels have been stimulated to open
- transient-type Ca2+ channels
Does Ca2+ have a higher conc inside or outside the cell?
higher conc outside
move into the cell
What type of ca2+ channel do funny type Na+ channels open?
transient-type Ca2+ channels
What happens when the Ca2+ move into the cell via transient-type Ca2+ channels?
further depolarisation
bring membrane to threshold
What occurs when a threshold has been reached?
an action potential can be initiated
At threshold what type of Ca2+ channels are opened?
Long-lasting Ca2+ channels
What occurs the long lasting Type calcium channels are open?
further depolarisation and gives rise to the upstroke of AP
When do the L-type Ca2+ channels close?
at the peak of the AP
are only open transiently
What channels are stimulated to open at the peak of AP?
voltage gated potassium channels
What direction will k+ flow through its channel?
more K+ inside that outside
will flow to the outside of the cell
down their conc gradient
What happens to the membrane potential when voltage gated K+ channels open?
mp becomes more negative
What current is. generated when K+ leave the cell?
ionic current
What does the ionic current give rise to in the AP?
the downstroke of AP
What does hyperolarisation of the membrane potential stimulate?
funny Na+ channels
the next pacemaker potential is spontaneously initiated
Why are they called funny channels?
typically voltage gated channels open when the mp becomes depolarised
but these channels open up when the potential becomes more negative at the end of re-polarisation form the previous AP
Why is the cardiac ca2+ induced phase different from skeletal and nerve muscle?
cardiac: Na+ influx
skeletal and nerve: Ca2+ influx that makes the potential much more +ve
