SA Node - Pacemaker cells
in the pacemaker cells K permeability is lower than Myocardial calles and so RMP is less negative and the RMP generates APs spontanously rhythmically and at varying rates
this allows fro hearbeat
SA action potential
the action potential is split into 4 bits
phase 4 is the prepotential zone. before depolarisation there is a depolarising tendency due to funny sodium channels. these are opened by hyperpolarisation. and there is less potassium as well
just before theshold T type calcium channels give a little positive “Boost” to threshold at the threshold slow (L) type Calcium channels open letting calcium in.
PHase 0 is peak
Phase 3 is late repolarisation repolarisation happens which hyperpolarises the pacemaker cell which then activates funny sodium channels again
Autonomic control of heart rate
N.B. Vagus nerve - goes everywhere - vagrant nerve
NA increase sodium and calcium permeability this increases slope of contration
see this
Ach decreases cAMP Na increases cAMP
Atropine blocks Ach?
Parasympathetic stimulation of the SA node reduces slope of the action potential and hyperpolarised SA node. Natural SA node rate is around 100 bpm
PSNS has baseline activity to lower resting HR
AV has 40-50 bpm purkinje fibres 20-30 therefore SA node is dominant (normally…)
path of electrical conduction
will maybe fill in later
syncytium - allows electrical impulse to traval through myocardium
conduction velocity of the tissue of the heart
atria 0.5 ms av node 0.05 ms bundle of his 1ms purkinje 5 ms vetricular myocardium 0ms-1
Ventricular muscle cell action potential
after depolarisation Ltype ca channels open and keep cell positive (phase 2 (plateau))