Lecture 3 - Heart Rate and Electrical Impulses Flashcards
4 key parts of blood circulation:
- self-generated rhythmical impulse
- move electrical signal from atria to ventricles at right time
- have atria contract before ventricles
- all parts of ventricles contract simultaneously
What are Purkinje fibers?
Fast conducting fibers that facilitate the synchronised conduction of ventricles.
Purpose and discharge speed of Sinoatrial node:
Pacemaker, discharges ~70 times per minute
When Calcium channels open in the cardiac cycle…
They cause full blown action potential, positive spike in mV
Why is the sinus node the pacemaker instead of A-V node or Purkinje fibers?
Sinus discharges faster (A-V next fastest than Purkinje)
How long does it take to travel down the internodal pathway?
0.03 seconds
How does the A-V node delay contraction, and why?
A-V node delays A-V bundle by 0.16 seconds total so atria fill ventricles before they contract.
Delay is due to the low number of gap junctions in the cells so slow conduction.
The transmission time between A-V bundles and last of the ventricular fibers is….
0.06 seconds - fast due to many gap junctions and intercalated disks
Why do the atria contract slowly?
To give time for blood to fill up the ventricles
Parasympathetic effects on heart rate include:
Hyperpolarisation decreases transmission of impulses, slowing heart rate
What happens during ventricular escape?
Nodes become silent, ectopic pacemaker, and A-V node or Purkinje take over
Sympathetic effects on heart rate include:
Norepinephrine causes increased sinus discharge so faster heart rate, faster conduction of impulse, increased force of contraction
Time between beginning of atrial contraction and beginning of ventricular contraction is which interval on an EKG?
P-R (0.16 seconds)
Q-T interval in EKG?
Time of ventricular contraction
Name 5 causes of cardiac arrhythmias:
- Abnormal rhythmicity of pacemaker sinus
- Ectopic pacemaker
- spontaneous generation of abnormal impulses
- Blocks in cardiac impulse transmission
- Abnormal transmission pathways
