Lecture 3 Heart Rate and Electrical Impulses

Question 1

4 key parts of blood circulation:

Answer 1

• 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

Question 2

Purpose of Purkinje system:

Answer 2

Purkinje fibers are fast conducting fibers that facilitate the synchronised conduction of ventricles.

Question 3

Purpose and discharge speed of Sinoatrial node:

Answer 3

Pacemaker, discharges ~70 times per minute

Question 4

When Calcium channels open in the cardiac cycle…

Answer 4

They cause full blown action potential, positive spike in mV

Question 5

Why is the sinus node the pacemaker instead of A-V node or Purkinje fibers?

Answer 5

Sinus discharges faster (A-V next fastest then Purkinje)

Question 6

How long does it take to travel down the internodal pathway?

Answer 6

0.03 seconds

Question 7

How does the A-V node delay contraction, and why?

Answer 7

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.

Question 8

The transmission time between A-V bundles and last of the ventricular fibers is….

Answer 8

0.06 seconds - fast due to many gap junctions and intercalated disks

Question 9

Why do the atria contract slowly?

Answer 9

To give time for blood to fill up the ventricles

Question 10

Parasympathetic effects on heart rate include:

Answer 10

Hyperpolarisation decreases transmission of impulses, slowing heart rate

Question 11

What happens during ventricular escape?

Answer 11

Nodes become silent, ectopic pacemaker, and A-V node or Purkinje take over

Question 12

Sympathetic effects on heart rate include:

Answer 12

Norepinephrine causes increased sinus discharge so faster heart rate, faster conduction of impulse, increased force of contraction

Question 13

P-R interval in EKG?

Answer 13

Time between beginning of atrial contraction and beginning of ventricular contraction

Question 14

Q-T interval in EKG?

Answer 14

Time of ventricular contraction

Question 15

Name 5 causes of cardiac arrhythmias:

Answer 15

• Abnormal rhythmicity of pacemaker sinus
• Ectopic pacemaker
• Generating abnormal impulses
• Blocks in cardiac impulse transmission
• Abnormal transmission pathways

Question 16

Tachycardia means?

Answer 16

A faster heart rate, over 100bpm

Question 17

What could cause tachycardia?

Answer 17

Increased body temp, sympathetic stimulation, decreased volume, toxicity, weak heart

Question 18

Brachycardia means?

Answer 18

A slow heart rate, below 60bpm

Question 19

What could cause brachycardia?

Answer 19

Athleticism, decreased body temperature, parasympathetic stimulation, toxicity

Question 20

What happens during isovolumetric contraction?

Answer 20

Ventricles continue contracting, so pressure in the left ventricle increases with no change in volume