112 Cardiac Muscle Contraction

Question 1

Organization of heart muscle

Answer 1

Question 2

Intercalated Discs

Answer 2

Question 3

Direction through heart of cardiac conduction

Answer 3

Question 4

Myocardial action potential current overview

Answer 4

Question 5

Calcium-induced calcium release

Answer 5

Question 6

Relationship between depolarization, Ca+2, Tension in cardiac myocyte

Answer 6

Question 7

Contractile stuructre of sarcomere

Answer 7

Question 8

Thin Filament

Answer 8

Question 9

Thick Filament

Answer 9

Question 10

Interaction b/w thick and thin filaments

Answer 10

Question 11

Cross bridge cycling

Answer 11

Question 12

Relaxation of sarcolemma

Answer 12

Question 13

Contractility

Answer 13

Contractility is the intrinsic strength of contraction independent of loading conditions

Examples of how contractility is potentiated:

• oAdrenergic Signalling
  
  • oPhosphorylation of phospholamban
  • oPhosphorylation of troponin I
• oDigoxin
• oHeart rate Effects on Contractility
  
  • oAscending Staircase
  • oRest Potentiation
  • oPost-Extrasystolic Potentiation

Question 14

Adrenergic signaling in cardiomyocytes

Answer 14

Question 15

Phospholamban and lusitropy

Answer 15

Question 16

Digoxin mechanism

Answer 16

Question 17

HR Effects: Ascending Staircase AKA Bowditch effect AKA Treppe

Answer 17

Post-Extrasystolic Potentiation:

Premature ventricular contraction (PVC, extrasystole) à less time for [Ca2+] to be removed from cell during relaxation (PVC beat itself is not strong because heart is in relative refractory period) à increased [Ca2+] available during heart beat à increased contractility of the post-PVC beat (post-extrasystole)

Question 18

Preload effect on sarcomere length/Tension

Answer 18

Preload is tension “stretch” on the heart prior to contraction.

Passive length-tension: difference explained by titin (rather stiff spring, therefore skeletal with no titin not a real springy)

Starling’s Law: Greater Fiber Length-> More Developed Tension

Question 19

Frank-Starling Curve

Answer 19

• •Increased Calcium Sensitivity at Greater Length, perhaps through greater actin/myosin proximity à More Contraction
• •Stretch-activated Ca2+ channels à More contraction
• •Old idea, not correct: more total overlap

Question 20

Afterload

Answer 20

Afterload is the load against which muscle must contract.

We approximate afterload clinically with blood pressure.