Cardiac Muscle Physiology

Question 1

Cardiac and Skeletal Muscle Similarities

Answer 1

 Striated  Sarcomeres  Cells short, branch &interdigitate  Strong union between fibers (intercalated disks)  T tubules and SR  Sarcomere & Thick/Thin Filaments are similar to those in skeletal muscle  Crossbridge cycling similar to those in skeletal muscle  Same Sliding Filament mechanism applies

Question 2

Cardiac cells are similar to _____ skeletal muscle fibers.

Answer 2

type I (slow oxidative) depend on oxidative phosphorylation, numerous mitochondria, highly resistant to fatigue but highly dependent on a continuous supply of O2

Question 3

What is an Intercalated disk?

Answer 3

site where cell-cell communication occurs (3 types of connections)

Question 4

Physical couplings of cardiac cells

Answer 4

points where cells mechanically pull on each other

Question 5

Functional couplings

Answer 5

allow electrical signals to pass between cells

Question 6

Gap Junctions assure that heart muscles can work as ____

Answer 6

as a synchronized unit but also can effectively uncoupling metabolically compromised cells

Question 7

Cardiac and Skeletal Muscle differences in excitation-contraction coupling

Answer 7

 more sparse SR  different T-tubes position - cardiac at z-line - skeletal A-I band junction  bigger T-tubes diameter - (200 nm vs 30 nm)  dyads instead of triads

Question 8

Skeletal E-C Coupling

Answer 8

Question 9

Key players in Ca²⁺ balance:

Answer 9

Ca2+ Entry:

• DHPR
• RyR

Ca2+ Exit:

• SR ATPase
• Surface ATPase
• Surface Na-Ca Exchanger
• Mitochondrial uniporter

Question 10

Role of L-Type Channels

Answer 10

Question 11

Cardiac Muscles Lack Summation

Answer 11

Question 12

Cardiac Contraction

Answer 12

Question 13

Autonomic Regulation of Cardiac Contraction

Answer 13

Question 14

Intrinsic Modulation of Cardiac Contraction

Answer 14

Question 15

Factors that influence the length of ventricular cardiac muscle fibers

Answer 15

Question 16

Negative inotropic agents ____ the force of contraction

Positive inotropic agents ____ the strength of contraction

Answer 16

Negative inotropic agents weaken the force of contraction

Positive inotropic agents increase the strength of contraction

Question 17

Positive Inotropic Agents

Answer 17

• Catecholamines :
  
  • Epinephrine or Norepinephrine (increase Ca2+ influx)
• Cardiac Glycosides :
  
  • Digitalis (inhibits Na-K ATPase; digoxin)
• Xanthines :
  
  • Caffeine and theophylline (inhibit the breakdown of cAMP)

Question 18

Negative Inotropic Agents

Answer 18

• β blockers (blocks β-Adrenergic Receptors)
• Diltiazem, Verapamil (block DHPR Ca2+ channels)

Question 19

In ventricular contraction:

Preload is:

Afterload is:

Answer 19

Preload is the stretch of the fibers by the blood during ventricular filing

Afterload is everything that opposes to ventricle contraction

Question 20

The force of contraction depends on:

Answer 20

• Intrinsic modulation by Frank-Starling’s Law.
  
  • change in INITIAL FIBER LENGTH (the main determinant of cardiac muscle fiber length is the degree of diastolic filling)
• Extrinsic modulation
  
  • change in CONTRACTILITY (related to intracellular [Ca2+] )

Question 21

Extrinsic Modulation of Cardiac Contraction

Answer 21

• The amount of Ca2+ release to the myofilaments
• The affinity of the myofilaments for Ca2+
• The alteration in the number of myofilaments available to participate in the contrac#on process.