Heart 1 (innervation) Flashcards
(32 cards)
what is the ‘overall’ innervation of heart contraction
1) pacemaker myocardial cells in the sino atrial node spontaneously innervate
2) depolarizing neighboring cells conduction to left atrium via bachmann’s bundle
3) ATRIAL systole
4) signal transfered via internodal pathway to AV node
5) Delay
6) Conduction through septum through bundle of his to branches of purkinjie fibers in both ventricles
7) ventricular SYSTOLE
what are the timings between the steps for ‘overall’ innervation of heart contraction
1) SA node 0.05m/s
2)atrial systole 1m/s
3)delay to ventricles 2-4m/s
4)ventricular systole 0.3-1m/s
ECG cardiac cycle sections and corresponding contraction part
P wave: atrial systole
PR segment: delay
QRS: ventricular systole
ST segment: repolarization of ventricle
T wave: ventricular diastole
how is innervation regulated by peripheral nervous system?
involved nerves
Parasympathetic: vagus nerve releases Ach reducing sino atrial innervation
Sympathetic: thoracic spinal nerve releases NA increasing excitation of SA node
what does the parasympathetic nervous system do to the heart
bradycardia <60bpm
what does the sympathetic nervous system do to the heart
tachycardia >100bpm
what else regulates the innervation of the heart (not PNS)
Inspiration = tachycardia
expiration = bradycardia
How are action potentials generated in pacemakers?
1) FUNNY channels open at <-40mv slow Na+ influx
2) at -55mv funny channels close and T-VACC open for slow depolarisation
3) -45mv L-VACC open for fast depolarisation
4) peak at 40mv Voltage gated K+ channels open for rapid repolarisation and T/L channels close
How are action potentials generated in cardiomyocytes?
1) innervated by adjacent cells by gap junctions
2) -65mv Voltage gated sodium channels open (rapid depolarisation)
3) peak at 40mv causes L-VACC and voltage activated K+ channels open causing plateau
4) increased intracellular Ca2+ for contraction causes SR to release more
5) L-VACC close and K+ remain open for repolarisation
6) intracellular Ca2+ reuptake into SR
what is different between pacemaker and myocardium refractory periods?
myocardium take longer to repolarise to baseline to prepare for secondary action potential
types of refractory period
Effective
Relative
relative refractory period….
a second action potential can be generated with a stimulus of high intensity (after repolarisation)
effective refractory period….
NO AP can be generated regardless of stimuli (Plateau phase)
how do cardiomyocytes maintain refractory period duration?
sodium voltage gated channels cannot be opened until around -50mv
what Classes of anti-arrhythmic drugs treat cardiomyocytes and MoA
Class 1 -> VA Na+ channel opening
Class 4 -> plateau Ca2+ opening
Class 3 -> repolarisation by K+
what class of anti-arrhythmic drugs can treat pacemakers and MoA
Class 4 -> FUNNY channels
how are pacemakers regulated by the sympathetic NS?
beta receptor GsPCR bound with NA (released for thoracic spinal nerve) inhibits activates adenyl cyclase increasing cAMP
cAMP binds to funny channel -> open
how are pacemakers regulated by the parasympathetic NS?
Muscarinic (M2) GiPCR bound with ACh (released by vagus nerve) inhibits adenyl cyclase so reduced cAMP
funny channel closed
what drugs can treat funny channels of pacemaker cells?
SNS: atenolol (beta blockers) reduce HR
PSNS: Digioxin
BLOCK: Ivabradine
what does Arrhythmia mean
change in heart beat rhythm that is abnormal
how are arrhythmias classified
HR, rhythm, site of origin, shape of QRS ECG trace
how are arrhythmia sites of origin classified
supraventricular (before)
ventricular (after)
general symptoms of arrhythmias
palpitations, chest pain, short breath and cardiac arrest
how are arrhythmias diagnosed
ECG trace
