Purkinje fibers

Question 1

Purkinje fibers size/morpho/fct

Answer 1

AV bundle + ventricular endocardium
* Size: LARGER = 150-200um x 34-40um
* Large and long pale ¢
o Contain a fewer contractile filament (myofibers) and mitochondria => located peripherically
o No T tubules
* Central and abundant glycogen
o Significant anaerobic energy production
* Prominent intercalated discs and gap junctions => fast end to end transmission

FUNCTION: rapid conduction of electrical impulse

Question 2

Myocytes size/morpho/fct

Answer 2

• Size: SMALLER = 50-100um x 10-25um
• Long and narrow ¢ with single centrally located nucleus
  o Filled with cross-striated myofibers and mitochondria
  o Plenty of T tubules
• Prominent end to end transmission (vs atrial myocytes also have side to side)
• Little interstitial collagen

FUNCTION: contraction => adapted to generate pressure

Question 3

Purkinje cell penetration: species differences

Answer 3

Divided according to time-order of ventricular activation

Category A: 3 waves of depolarization = dog, human, primates, cat, rat

Category B: 3 waves of depol. = horse, cow, goat, pig, sheep
More general penetration of Purkinje fibers into epicardium

Question 4

Category A penetration fibers

Answer 4

1. Initial depolarization (first 5-10ms of QRS): endocardium around apex of LV
2. Depolarization of both free walls (next 15ms of QRS) from endocardium to epicardium
3. Terminal depolarization of the R + L basilar region + IVS (last 5ms of QRS)

Question 5

Category B penetration fibers

Answer 5

More general penetration of Purkinje fibers into epicardium
1. Initial activation similar = endocardium around apex of LV
2. Terminal depolarization of 2/3 basilar IVS from apex to base. As the 1st wave ends, a 2nd wave will depolarize the major ventricular mass (L and R free walls) as a single burst.
a. Many polarity exist w/i the free wall

Question 6

Properties useful for impulse conduction

Answer 6

• Larger ¢ (3x wider vs vemtricular myocytes) => decr resistance to electrical conduction as ¢ diameter incr
• Few myofibrils and T tubules => decr resistance to internal conduction
• Packed tightly together => diameter effectively available for conduction is the entire bundle rather than individual ¢
• High # of intercalated disc/end-to end junctions => facilitate rapid propagation of electrical impulse

Question 7

Histo of false tendon

Answer 7

False tendon contain Purkinje fibers => travels directly inside the ventricular cavity

Question 8

False tendon other name

Answer 8

left ventricular muscular bands

Question 9

Unique characteristic of canine purkinje fibers