cardiac muscle Flashcards

1
Q

what is the function of conductile cells of cardiac muscle? Name the different kinds

A
  • function: rapid spread of electrical signal (action potential) through myocardium
  • kinds
    • bundle of his
    • purkinje fibers
    • SA node
    • AV node
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2
Q

conducting cells can generate what type of action potentials

A

spontaneous

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3
Q

what conductile cells are the primary pacemakers

A

Sinoatrial (SA) node

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4
Q

function of cardiac myocytes

A

contractile cells: contraction

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5
Q

list the spread of excitation

A
  1. SA node: initiates action potential
  2. spread to atria and AV node
  3. AV node: slow conduction
  4. bundle of his and purkinje fibers : fast conduction
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6
Q

depolarization of ventricular myocardium goes from what level to what level

A

from endocardium to epicardium

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7
Q

what is conduction velocity

A

speed of action potential propagation through heart

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8
Q

what conductile cells have the fastest and slowest conduction velocity

A

slowest: AV node: 0.01-0.05 m/sec
fastest: Bundle of his and purkinje fibers: 2-4 m/sec

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9
Q

what dictates the conduction velocity

A
  1. rate of change in membrane potential as a function of time (i.e. upstroke phase of action potential)
  2. resistance
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10
Q

compare duration of action potentials of cardiac vs skeletal muscle

A

cardiac AP have a longer duration

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11
Q

compare action potentials between contractile cells and pacemaker cells

A
  1. contractile cells: fast AP
  2. pacemaker cells: slow AP
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12
Q

what is phase 0 of fast action potential

A
  • upstroke, rapid depolarization
  • fast inward Na+ current
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13
Q

what is phase 1 of fast action potential

A
  • early repolarization
  • activation of K+ channels: K+ moves out
  • inactivation gates on Na+ channels close
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14
Q

what is phase 2 of fast action potential

A
  • Plateau phase
  • responsible for the very long AP
  • due to balance between Ca2+ (L-type channel: inward) current and K+ outward current
    • L-type = long lasting: have slower kinetics than “fast” Na+ channels
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15
Q

what is phase 3 of fast action potential

A
  • repolarization
  • turn off of Ca2+ current and further increase in K+ current
  • K+ current reduced near end of phase 3 because membrane potential closer to K+ equilibrium
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16
Q

what is phase 4 of fast action potential

A
  • resting potential
  • caused by K+ outward current
    • different channels thatn phase 3
  • balanced by inward Na2+ and Ca2+ current
17
Q

why is summation and tetanus of cardiac muscle unlikely

A

because long refractory period occurs in conjunction with prolonged plateau phase

* this is good because it ensures alternating periods of contraction and relaxation which are essential for pumping blood

18
Q

Key differences of sinoatrial (SA) node slow action potential

A
  1. automatically
  2. unstable resting membrane potential
  3. no sustained plateau

* phase 1 and 2 are absent

19
Q

what is phase 0 in SA node slow action potential

A
  • upstroke
    • slow due to inward long-lasting Ca2+ current
20
Q

what is phase 3 in SA node slow action potential

A
  1. repolarization
  2. turn-off of Ca2+ current
  3. further increase in K+ current
21
Q

what is phase 4 in SA node slow action potential

A
  • pacemaker potential
    • spontaneous depolarization
    • longest portion
  • (If) inward Na+; inward T-type Ca2+ current
  • If turned on by repolarization from preceeding AP
22
Q

rate of what phase sets heart rate

A

phase 4 in SA node slow action potential

23
Q

cardiac muscle cells are interconnect by what feature that helps form functional syncytium

A

intercalated disc

24
Q

within the intercalated discs, there are two kinds of membrane junctions, name them

A
  1. desmosomes: mechanical junctions
  2. gap junctions: electrical junctions
25
Q

what molecule initiates excitation-contraction coupling in cardiac contractile cells? What is the source?

A
  • CA2+
  • extracellular Ca2+ (differs from intracellular Ca2+ used in skeletal muscle)
26
Q

list the steps of excitation-contraction coupling in cardiac contractile cells

A
  1. excitation: AP causes the depolarization of the membrane
  2. Ca2+ channels open (during plateau of AP)
  3. Ca2+ enters cell
    1. Ca2+ - induced Ca2+ release form SR
  4. Ca2+ binds to troponin
  5. crossbridge cycling
27
Q

how is calcium removed from cytoplasm during relaxation

A
  1. uptake into SR: SERCA pump contributes to majority of CA2+ flux
  2. uptake into mitochondria
  3. Na+/K+ ATPase and NCX pump which create gradient for calcium removal
28
Q

function of drugs Digitalis and Digoxin

A
  • mechanism: inhibit the Na+/K+ ATPase and therefore reverse the Na+/Ca2+ exchanger so that now there is higher intracellular CA2+
  • result: enhances force of contraction (contractility)