Cardiac Muscle 2

Question 1

One of the main characteristics of working myocardium compared to other cell types APs is?

Answer 1

• Repolarization toward resting potential is hundreds of times slower
• Makes duration of AP much longer

Question 2

______________ mediate the rapid upstroke in atrial, ventricular, and purkinje fibers APs, like skeletal and nerve fibers.

Answer 2

Voltage gated Na+ channels

Question 3

T-Type Ca2+ channels

Answer 3

• generate spontaneous APs in SA and AV nodal cells
• faster inactivation than type L Ca2+ channels
• activate between -80 and -40 mV

Question 4

L-Type Ca2+ channels

Answer 4

• activate between -30 and 0 mV
• inactivate slowly (slower than T-type)
• carry plateau of cardiac APs (working myocardium and perkinje/bundle of His)

Question 5

Inward Rectifier K+ channel

Answer 5

• responsible for major portion of resting conductance
• high conductance at negative potentials
• DOES NOT CONTRIBUTE TO PLATEAU

Question 6

Delayed Rectifier K+ channel

Answer 6

• activates slowly at positive potentials
• contributes to plateau!!
• partly responsible fro terminating plateau and final repolarization

Question 7

The atrial action potential closely resembles the ventricular AP except that it has more phase 1 repolarization and more sloping plateau. What does this indicate?

Answer 7

-There is more outward current relative to inward current

Question 8

What depolarizes the membrane in SA/AV node cells?

Answer 8

• Ca2+ (T-type)

- explains the slower rate of phase 0 compared to working myocardium Na+ induced fast phase 0

Question 9

SA and AV node maximum level of diastolic polarization vs. working myocardium

Answer 9

• increased: -60 to -70 vs. -80 to -90

- indicates less permeability for K+ relative to inward currents

Question 10

Conducing cells (SA, AV, Purkinje, bundle of His) phase 4 uniqueness

Answer 10

-There is a marked phase 4 diastolic depolarization

Question 11

Plateau in Purkinje fiber AP vs. working myocardium

Answer 11

-Must lower (more negative)

Question 12

Adjacent heart cells are electrically coupled by gap junctions at the _________ and along their _______ borders.

Answer 12

• Intercalated discs

- Lateral borders

Question 13

The current that flows from an active region of the heart into a resting region is carried mainly by _____ ions inside the cell and between them through gap junctions. The return circuit flows through the extracellular space by movement of _____ and ______. Current into the active tissue is the _____ and ______ cureents that activate its AP.

Answer 13

K+

Na+ and Cl-

Na+ and Ca2+