Flashcards in Physiology Deck (25):
capable of beating rhythmically without an external stimuli
Where does the excitation originate?
pacemaker cells in the SA node (Upper RA near SVC opening)
A heart controlled by SA node is called
Route of spread of excitation?
SA mode through both atria
SA node to AV node
Gap junction within ventricles
what, where and how AV node
small bundle of specialised cardiac cells, base of right atrium (ONLY point of contact between ventricles and atriums.
mainly gap junction cell-to-cell but some internodal. with delayed conduction to allow atrial systole to precede. the bundle of HIS and Purkinji fibres allows quick spread
What are the phases of ventricular muscle action potential?
Phase 0: Fast Na+ influx
Phase 1: closure of Na+ channels and transient K+ efflux
Phase 2: mainly Ca++ influx
Phase 3: Closure of Ca++ channels and K+ efflux
Phase 4: resting membrane potential
What is the plateau phase of ventricular muscle action potential and what cells is it unique to?
membrane potential is maintained near the action potential peak. unique to contractile cardiac muscle cells.
influx of Ca++ though ligand channels.
Falling phase of ventricular muscle?
inactivation of Ca++ channels are inactivated and K+ channels activation (efflux K+) causes repolarisation.
HR is affected by which system? and what subset in what way?
sympathetic increases HR
parasympathetic increases HR
what nerve is the parasympathetic supply to the heart
Vagal tone dominates under what conditions and slows what HR to what resting rate?
under resting conditions
slows ~100 bpm to 70 bpm
what is normal resting rate?
60 - 100 bpm
HR <60bpm aka...
HR >100bpm aka...
If the vagus nerve supplies the AV node and the SA node what 2 things can it effect?
slows HR, increases AV nodal delay
what neurotransmitter is sent by the parasympathetic nerves to the heart and what through?
acetylcholine (through the muscarinic M2 receptors)
what effect does atropine have on neurotransmitter
what sympathetic supply is to the heart and to what areas?
cardiac sympathetic nerves
SA/AV node & myocardium
sympathetic stimulation does what?
increases HR and decreases A nodal delay
what neurotransmitter is sent by sympathetic nerves to the heart and what through?
noradrenaline through beta1-adrenoreceptors.
cells in SA don't have what?
a stable resting membrane potential
what is spontaneous pacemaker potential
it takes the membrane potential to a threshold to generate an action potential in SA nodal cells
what causes the slow depolarisation of membrane potential to a threshold (pacemaker potential)? (3)
decrease in K+ efflux
Na+ & K+ efflux
transient Ca++ influx (t-type channels)
what 2 phases occur once threshold is reached (pacemaker cells) and what is involved
the rising phase = activation of long lasting (l-type Ca++ channels that means a Ca++ influx
the falling phase = inactivation of l-type Ca++ channels & activation of K+ channels that means a K+ efflux