Phys Lecture I Cardiac excitation Flashcards
Where does sympathetic stimulation to the heart originate?
Medulla Oblongata
What nerve carries the parasympathetic innervation to the heart?
Vagus Nerve.
Is there parasympathetic innervation to the ventricles?
No
Where do the parasympathetic branches go to?
SA and AV node
What structure in the heart is the main pacemaker i.e spontaneously generates action potentials which cause cardiac excitation/contraction?
SA node
How does electrical activity travel from SA to AV node?
Internodal pathways
How long does it normally take for a complete ventricular electrical cycle?
200msec
What channel maintains the cells in a highly polarized state?
Ik1
At what voltage do the sodium channels get activated?
-60mv
How is the Ca2+ channel activated?
Voltage activated channel
What channelis responsible for PHASE 1? The transient repolarization?
Ito. This is called the transient outward channel and is responsible for the transient outward flow of K+ ions
How is the Potential maintained during PHASE 2?
Outward flow of K+ and inward flow of Ca2+
What is significant about the If channel?
It is a Na channel which becomes activated while the cell is polarized and turn off when the cell is depolarized
What ion is responsible for the post threshold polarization of SA nodal cells?
Influx of Ca2+
What tissues have the fastest conduction rates?
Bundle of HIS and Purkinje cells
What is the intrinsic rate of the SA node absent any neuro influence?
100-120 beats per minute
What two sets of tissues can under pathological states develop their own spontaneous activity and serve as pacemakers?
- Atrial Muscle
2. Ventricular muscle
What are the effects of parasympathetic activity on the heart?
- Decreases Heart rate
- Decreases conduction velocity particularly in the AV node
- Decreases excitability of latent pacemakers
What are the effects of Sympathetic activity on the heart?
- Increases HR
- Increases conduction velocity (particularly in the AV node)
- Decreases the threshold of Ca channels:Increases excitability of Latent pacemakers nd other cells
What is the neurotransmitter of the parasympathetic activity?
Acetylcholine
What is the neurotransmitter of cardiac sympathetic activity?
Norepinephrine
Which activity prevails when it comes to the SA node?
Paraympathetic
