IBHRE UPDATED ACTUAL Exam
Questions and CORRECT Answers
SA Node - CORRECT ANSWER - - dense collagen matrix
- p cells surrounded by transitional cells and fiber tracts that extend through RA
Bachman's Bundle - CORRECT ANSWER - Conducts impulse through both atria
AV Node - CORRECT ANSWER - - subendocardial structure within interatrial septum
- looser collagen matrix of p cells + transitional cells
- regulates # impulses conducted to reach ventricles
How is excitability maintained? - CORRECT ANSWER - Separation of charge
[Na+]out & [K+]out - CORRECT ANSWER - 145mmol/L and 4.5mmol/L
Na+/K+ ATPase pump - CORRECT ANSWER - Active transport mechanism
- 3 Na+ ions out and 2 K+ in per ATP
- ATP phosphorylation/dephosphorylation causes conformational changes to transport ions
Resting membrane potential - CORRECT ANSWER - -90mV (inside more negative)
Membrane potentials in pacemaker cells - CORRECT ANSWER - Slowly become more
positive on the inside until it reaches a membrane threshold potential (-70 to -60 mV)
Faraday constant - CORRECT ANSWER - 96,500 coulombs = amount of charge that a
mole of electrons has
, Phase 0 - CORRECT ANSWER - Once membrane threshold is reached, the channels
change to an open configuration to allow for sodium ions to flood inside, making potential about
20mV
Phase 1 - CORRECT ANSWER - Sodium channels become inactivated
Potassium channels open and close - letting potassium out to make potential more negative
Phase 2 - CORRECT ANSWER - Plateau phase as membrane slowly depolarizers
- inward calcium ions and sodium ions balance outward potassium ions
- calcium ions activate chloride channels
What phase does absolute refractory occur? - CORRECT ANSWER - Phase 2
Importance of calcium ions - CORRECT ANSWER - Responsible for contraction of the
heart
Phase 3 - CORRECT ANSWER - Rapid depolarization to normal membrane potential
- K+ channels remain open which results in net outward positive current, making membrane
potential more negative
- calcium pumped out resulting in muscle relaxation
Phase 4 - CORRECT ANSWER - Gradual updrift in transmembrane potential
What is a major factor responsible for resting membrane potential? - CORRECT
ANSWER - Equilibrium potential for potassium ions because the membrane is more
permeable to potassium
Anisotropy - CORRECT ANSWER - unequal physical properties along different axes
Questions and CORRECT Answers
SA Node - CORRECT ANSWER - - dense collagen matrix
- p cells surrounded by transitional cells and fiber tracts that extend through RA
Bachman's Bundle - CORRECT ANSWER - Conducts impulse through both atria
AV Node - CORRECT ANSWER - - subendocardial structure within interatrial septum
- looser collagen matrix of p cells + transitional cells
- regulates # impulses conducted to reach ventricles
How is excitability maintained? - CORRECT ANSWER - Separation of charge
[Na+]out & [K+]out - CORRECT ANSWER - 145mmol/L and 4.5mmol/L
Na+/K+ ATPase pump - CORRECT ANSWER - Active transport mechanism
- 3 Na+ ions out and 2 K+ in per ATP
- ATP phosphorylation/dephosphorylation causes conformational changes to transport ions
Resting membrane potential - CORRECT ANSWER - -90mV (inside more negative)
Membrane potentials in pacemaker cells - CORRECT ANSWER - Slowly become more
positive on the inside until it reaches a membrane threshold potential (-70 to -60 mV)
Faraday constant - CORRECT ANSWER - 96,500 coulombs = amount of charge that a
mole of electrons has
, Phase 0 - CORRECT ANSWER - Once membrane threshold is reached, the channels
change to an open configuration to allow for sodium ions to flood inside, making potential about
20mV
Phase 1 - CORRECT ANSWER - Sodium channels become inactivated
Potassium channels open and close - letting potassium out to make potential more negative
Phase 2 - CORRECT ANSWER - Plateau phase as membrane slowly depolarizers
- inward calcium ions and sodium ions balance outward potassium ions
- calcium ions activate chloride channels
What phase does absolute refractory occur? - CORRECT ANSWER - Phase 2
Importance of calcium ions - CORRECT ANSWER - Responsible for contraction of the
heart
Phase 3 - CORRECT ANSWER - Rapid depolarization to normal membrane potential
- K+ channels remain open which results in net outward positive current, making membrane
potential more negative
- calcium pumped out resulting in muscle relaxation
Phase 4 - CORRECT ANSWER - Gradual updrift in transmembrane potential
What is a major factor responsible for resting membrane potential? - CORRECT
ANSWER - Equilibrium potential for potassium ions because the membrane is more
permeable to potassium
Anisotropy - CORRECT ANSWER - unequal physical properties along different axes
