Origin and Conduction of Cardiac Impulse Flashcards
What initiates the heart beat in a normal individual?
The SA node
Where is the SA node located?
The right upper atrium close to the entry point of the SVC
What is it called when a heart is driven by the SA node?
Sinus rhythm
What is the pacemaker potential?
The slow depolarisation of the membrane
What causes the pacemaker potential?
Decrease in K efflux
Na and K influx (funny current)
Transient Ca influx (T type Ca channels)
What is the rising phase of action potential caused by?
Activation of long lasting L-type channels
What causes the falling phase of the membrane potential?
Inactivation of Ca channels and activation of K channels
Where is the AV node located?
The base of the right atrium between the junction of the atria and the ventricles
What is the importance of AV nodal delay?
Allows systole to precede diastole.
Describe the phases of the action potential on atrial and ventricular myocytes?
Phase 0 Fast Na+ influx Phase 1 Closure of NA channels and transient K influx Phase 2 mainly Ca influx Phase 3 Closure of Ca channels and k efflux Phase 4 resting membrane potential
What is a normal resting heart rate?
60-100bpm
What is the medical terms for slow and fast HR
Bradycardia and Tachycardia
What changes the Heart rate?
The ANS
What does the sympathetic and parasympathetic system do to the HR?
Sympathetic- increases
Parasympathetic-decreases
What dominates the heart in resting conditions?
Vagal tone
What does vagal stimulation do?
Slow the HR by slowing the rate of firing of the SA node and increases AV nodal delay
What is the parasympathetic neurotransmitter and which receptors do they act through?
ACH through M2 receptors
What is atropine?
Competitive inhibitor of ACH: used in extreme bradycardia to speed up the heart
Where is the sympathetic supply of the heart?
supplies SA node and AV node and myocardium
What is the sympathetic neurotransmitter and the receptor it works through?
noradrenaline acting through B1 adrenoreceptors
What is the effect of sympathetic stimulation on the pacemaker potential?
Slope increases and frequency of action potentials increase
What does the P wave represent?
Atrial depolarisation
What does the QRS wave represent?
Ventricular depolarisation
What does the T wave represent?
Ventricular repolarisation
What does the PR interval represent?
largely AV nodal delay
What does the ST segment represent?
ventricular systole
What does the TP interval represent?
diastole
