L9 - Electrical Activity of the Heart Flashcards
What three type of cells is the electrical activity spread by
Nodal cells
Conducting cells
Muscle cells
What type of structures conduct the electrical activity
Electrical synapses
Describe the overview of the process of excitation in the heart
Initiation at the SA node
Conduction to the atrioventricular node and then to the AV ring
Conduction to the left atria via brachmans bundle (interatrial tract)
Passage through thebundle of His
Purkinje system distributes to the ventricular muscle cells
The SA node acts as a
Pacemaker
What is another word for the interatrial tract
Brachmans bundle
Describe the location of the SA node
Posterior aspect
Junction superior vena cava and right atrium
What is the function of the interatrial tract
Spreads the depolarisation from the right atrium to the left atrium
Describe the location of the AV node
Posterior aspect - right side inter atrial septum
What are the three subzones of the AV node
AV N NV
What is the function of the AV node delay
To allow the atrial contraction to finish
What is the function of the AV node refractory period
Prevent excess ventricular contraction
What happens to the AV refractoriness as heart rate increases
It increase
Subnodal conduction leads to
Spetal activation - depolarisation of the septa
What can be said about the contraction of the heart
Spiral muscle contraction evoking a torsion
Process of depolarisation in the heart
Depolarise the atria
Depolarise in interventricular septum
Depolarisation of the anteroseptal region of the myocardium toward the apex
Ventricles now depolarised
Posterior portion of the base of the left ventricle now depolarised
Depolarisation of the bulk of the ventricular myocardium from the endocardium to the myocardium
Which three types of cells fire action potentials with plateau phases
Purkinje fibres
Atrial and ventricular muscle cells
Two properties of pacemaker cells
Automaticity
Rhythmicity
What is the primary pacemaker cells of the heart
SA node
What other cells are able to act as pacemakers
AV node
Purkinje cells
What is the rising phase of a pacemaker cells Vm leading to action potential firing
Prepotential
What is responsible for the prepotential
Decreased K efflux and increased cation influx
What current produces the prepotential
If
Describe the If current
Hypepolarisation induced, inactive when +ve
When is the If inactive
When +ve
What induces IF
Hyperpolarisation
What is the action potential of a pacemaker cell generated by
Fast Ca influx
What is repolarisation of the pacemaker cell caused by
Increased K efflux
What three regualtory mechanisms affect the pacemaker cell action potential
Innervation
Temperature
Other pacemaker cells
How do vagal fibres affect the pacemaker cells
Parasympathetic
Hyperpolarisation of the pacemaker cells and decrease slope of the pre potential
How does sympathetic stimulation affect the pacemaker cells
Increased prepotential slope and increased firing rate (threshold is reached much faster)
What chemical do pacemaker cells rely on
cAMP
What is the affect of Ach on the pacemaker cells
Acts on M2 receptors –> decreased cAMP production
Decreased prepotential slope - longer for threshold to be reached
What is the effect of NAdr on the pacemaker cells
Acts on beta adrenergic receptors –> increases the cAMP production
Increased prepotential slope - threhsold reached much quicker
Describe the action potential of the cardiac muscle
No automaticity
Long plateau
Propagated and prolonged action potential
Fast depolarisation and then overshoot
What causes the initial depolarisation of the cardiac muscle
Opening of the VGNC
what leads to a massive depolarisation of the cardiac muscle
Opening of many more VGNC
When do VGNC close (cardiac muscle
When depolarisation peaks
What is the peak Vm of the cardiac muscle
+30 mV
What causes the plateau phase of the cardiac muscle action potential
Ca slow channels open and Ca moves into the cell - maintaining the depolarisation
Why does the plateau phase of the cardiac muscle AP fall
K+ leak
What happens when the Ca channels close
cardiac muscle
K channels open, K moves out and the cell repolarises
What channel is involved with Ina
Nav1.5
What inhibits Nav1.5
TTX and Local anesthetics
What channel is involved in Ica
Cav1.2
What type of channel is Cav1.2
L type Ca channel
What can said about the number of K channels involved in Ik (repolarising current)
Many channels
What K channels are the main drivers for membrane repolarisation
Iks and Ikr
What channel is involved in the funny current
HCN4
What is HCN4 permeable to
Mostly Na some K
What is If inhibited by
Cs+
