U

Question 1

Pathway of initiation of cardiac electrical activity ???

Answer 1

SAN in right atrium ,
Action potentials Conducted through Atrial myocytes (0.5 m/sec) or 3 Internodal bundles (1 m/sec) AV node =at lower posterior atrial septum
• only pathway between atria & ventricles
• Slow Conduction (0.05 m/sec) due to Few gap junctions & Slow upstroke
A- Importance: Allow ventricular filling & Protect ventricles from abnormal high rhythm
Bundle of His & branches on each side of ventricular septum (2 m/sec.)
Purkinje fibers rapid conduction= (4 m/sec) →Allows coordinated contraction ventricular myocytes 0.5

Question 2

SAN node position and discharge how it’s action potential conducted to AV node

Answer 2

SAN in right atrium ,
Action potentials Conducted through Atrial myocytes (0.5 m/sec) or 3 Internodal bundles (1 m/sec)

Question 3

AV node position and velocity importance of its conduction velocity

Answer 3

at lower posterior atrial septum
• only pathway between atria & ventricles
• Slow Conduction (0.05 m/sec) due to Few gap junctions & Slow upstroke
A- Importance: Allow ventricular filling & Protect ventricles from abnormal high rhythm

Question 4

Bundle of His position and speed

Answer 4

branches on each side of ventricular septum (2 m/sec.)

Question 5

Purkinje fibers speed mention importance of its speed

Answer 5

rapid conduction= (4 m/sec) →Allows coordinated contraction
Then passes to ventricular myocytes 0.5

Question 6

Resting membrane potential
determined by..

Answer 6

Concentration gradient, Permeability, pumps)

Question 7

Causes of RMP = -90 mv

Answer 7

1- Efflux of K+ via inward rectifying potassium channels (conduct inward current in hyperpolarization 2- Influx of Na+ and Ca++ with low permeability
3- Na+-K+ ATPase: Pumps 3 Na+ out for 2 K+ in