Myogenic action potentials
action potentials created in heart muscle
Pacemaker cells
produce action potentials that allow the heart to beat
do not have a normal resting potential like other cells
where are pacemaker cells found
in three places - SAN, AVN, purkinje network/bundle of His
pacemaking ability by location
- SAN - highest rate of AP generation
- AVN - slower than SAN, not enough alone
- bundle of His/purkinje - very low contributor
what channels are found in pacemaker cells
no sodium channels
have funny channels
what are funny channels
Unique sodium channels found in pacemaker cells
what are contractile cells
99% of cardiac muscle cells
function in mechanical work of pumping
pacemaker cells process
membrane potential slowly depolarises or drifts between action potentials (pacemaker potential)
until threshold is reached
when an action potential is fired
ion movement for pacemaker potential
- increased inward Na+ current
- decreased outward K+ current
- increased Ca2+ current
why are funny channels different to normal channels
- activated by hyperpolarisation (more negative membrane) rather than depol (less negative membrane)
at the end of repol of the prev AP - membrane potential immediately moves toward threshold again after an AP - slow leak of inward Na+
- outflow of K+ ions gradually declines
Lowest membrane potential of funny channels
-60mv
Threshold of funny channels
-40mv
Peak of funny channels
10mv
Adrenaline signal cascade
- Binds onto channel receptors
- G proteins activate enzyme
- Enzyme turns ATP to cAMP
- Affects protein kinase
- cAMP opens calcium and funny channels
- Sodium and calcium enter cell
- Speeds up the heart
Specialised CONDUCTIVE cells
Pacemaker cells
Specialised CONTRACTILE cells
Cardiomyocytes
Conduction system is surrounded by
Fibrous collagenous tissue
Gap junctions function
To allow APs to flow to neighbouring cells
Evidence of gap junctions
Antibody stain - fluorescent labelling technique
Added to connexin - protein that makes gap junctions
Function of the cardiac skeleton
- Structure - for muscles to hold onto
- Valves - prevent back flow
- Non conductive = APs don’t leave conductive tissue, APs don’t travel straight from atria to ven (there is a pause)
L type calcium ion channels
Normal myocardial contractility
Activated when threshold is reached
Causes large Ca2+ influx - potential becomes more positive
T type calcium ion channels
Found in conducting and pacemaker cells
Effect of L type Ca ion channels
- long term
- allow Ca2+ in
- causes depolarisation
- myosin heads can bind with actin filaments
Channels only in pacemaker cells
Funny sodium channels
T type calcium channels
