Cardiac muscle physiology

Question 1

sarcomere elements

Answer 1

• go from z band to z ban
• thin filament area called the I band
• overlap of filaments is the A band
• thick filament zone is the H band

Question 2

latent pacemakers

Answer 2

cells other than the SA node exhibiting automaticity

Question 3

pacemaker rates

Answer 3

-SA>AV>bundle of HIS>purkinje

Question 4

ectopic pacemakers

Answer 4

latent pacemakers that become the pacemaker of the heart

Question 5

speed of conduction

Answer 5

purkinje>atria and ventricles> AV node

Question 6

AV node

Answer 6

delays electrical conduction between the atria and ventricles

Question 7

equilibrium potentials

Answer 7

• K is -95
• Na is +72
• Ca is +133
• determined by the number of open channels and by electrogenic ion pumps and exchangers

Question 8

fast reponse action potentials

Answer 8

• contractile myocytes

- atrial and ventricular

Question 9

slow response action potentials

Answer 9

• pacemaker myocytes

- SA and AV nodes

Question 10

fast response APs phase 4

Answer 10

• resting Em
• near Ek due to high K+ permeability
• dominated by IK1 (outward current due to activation of inwardly rectifying K channels)

Question 11

fast response APs phase 0

Answer 11

• rapid depolarization

- mediated by INa (inward current due to activation of voltage-dependent Na channels)

Question 12

fast response APs phase 1

Answer 12

• transient repolarization

- mediated by Na channel inactivation and activation of transient outward K current (iKto)

Question 13

fast response APs phase 2

Answer 13

• plateau

- mediated by inward current of Ca due to Ltype voltage gated Ca channles (CGCC) and outwards iK1

Question 14

fast response APs phase 3

Answer 14

• rapid repolarization

- mediated by iK (outward current due to activation of voltage-dependent K channels)

Question 15

slow response APs phase 4

Answer 15

• pacemaker potential
• inward funny current (If) carried mainly by Na+
• inward Ca currents mediated by T-Type and L type channels

Question 16

slow response APs phase 0

Answer 16

• slow depolarization

- mediated by iCaL

Question 17

slow response Aps phase 3

Answer 17

-mediated by iK (outward current due to activation of voltage-dependent K channels)

Question 18

conduction system summary

Answer 18

• SA node determines HR
• AV node: low conduction velocity; delays AP propagation between atria and ventricles
• Purkinje fibers: conduct impulses to ventricles leading to ventricular systole

Question 19

fast response APs summary

Answer 19

• characteristic of contractile myocytes

- stable phase 4; rapid phase 0; phase 2 plateau

Question 20

slow-response APs

Answer 20

• characteristic of pacemaker myocytes
• unstable phase 4 (pacemaker potential)
• slow phase 0; lack iNa (voltage gated Na channels

Question 21

excitation-contraction coupling

Answer 21

• altering Ca cytosolic concentrations
• during plataeu phase, L type VGCC open and Ca stimulated CICR on ryanodine receptors
• Ca binds to TnC and contraction occurs
• Ca inhibits the Ltype receptors
• SERCA pumps Ca back into the SR

Question 22

contraction

Answer 22

-depolarization leads to Ltype VGCC activation
-ryandone receptor is stimulated
=Ca released from SR
-increased Ca concentration

Question 23

cross bridge cycling

Answer 23

-Ca binds to TN-C on thin filament to initiate contraction

Question 24

relaxation

Answer 24

• inactivation of L type VGCC
• Ca reuptake to SR via SERCA
• Ca extrusion via the Na/Ca exchanger and Ca ATPase